fs/buffer.c

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This source file includes following definitions.
touch_buffer
__lock_buffer
unlock_buffer
buffer_check_dirty_writeback
__wait_on_buffer
__clear_page_buffers
buffer_io_error
__end_buffer_read_notouch
end_buffer_read_sync
end_buffer_write_sync
__find_get_block_slow
end_buffer_async_read
end_buffer_async_write
mark_buffer_async_read
mark_buffer_async_write_endio
mark_buffer_async_write
__remove_assoc_queue
inode_has_buffers
osync_buffers_list
emergency_thaw_bdev
sync_mapping_buffers
write_boundary_block
mark_buffer_dirty_inode
__set_page_dirty
__set_page_dirty_buffers
fsync_buffers_list
invalidate_inode_buffers
remove_inode_buffers
alloc_page_buffers
link_dev_buffers
blkdev_max_block
init_page_buffers
grow_dev_page
grow_buffers
__getblk_slow
mark_buffer_dirty
mark_buffer_write_io_error
__brelse
__bforget
__bread_slow
check_irqs_on
bh_lru_install
lookup_bh_lru
__find_get_block
__getblk_gfp
__breadahead
__breadahead_gfp
__bread_gfp
invalidate_bh_lru
has_bh_in_lru
invalidate_bh_lrus
set_bh_page
discard_buffer
block_invalidatepage
create_empty_buffers
clean_bdev_aliases
block_size_bits
create_page_buffers
__block_write_full_page
page_zero_new_buffers
iomap_to_bh
__block_write_begin_int
__block_write_begin
__block_commit_write
block_write_begin
block_write_end
generic_write_end
block_is_partially_uptodate
block_read_full_page
generic_cont_expand_simple
cont_expand_zero
cont_write_begin
block_commit_write
block_page_mkwrite
end_buffer_read_nobh
attach_nobh_buffers
nobh_write_begin
nobh_write_end
nobh_writepage
nobh_truncate_page
block_truncate_page
block_write_full_page
generic_block_bmap
end_bio_bh_io_sync
guard_bio_eod
submit_bh_wbc
submit_bh
ll_rw_block
write_dirty_buffer
__sync_dirty_buffer
sync_dirty_buffer
buffer_busy
drop_buffers
try_to_free_buffers
SYSCALL_DEFINE2
recalc_bh_state
alloc_buffer_head
free_buffer_head
buffer_exit_cpu_dead
bh_uptodate_or_lock
bh_submit_read
buffer_init
   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/fs/buffer.c
   4  *
   5  *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
   6  */
   7 
   8 /*
   9  * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
  10  *
  11  * Removed a lot of unnecessary code and simplified things now that
  12  * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
  13  *
  14  * Speed up hash, lru, and free list operations.  Use gfp() for allocating
  15  * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
  16  *
  17  * Added 32k buffer block sizes - these are required older ARM systems. - RMK
  18  *
  19  * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
  20  */
  21 
  22 #include <linux/kernel.h>
  23 #include <linux/sched/signal.h>
  24 #include <linux/syscalls.h>
  25 #include <linux/fs.h>
  26 #include <linux/iomap.h>
  27 #include <linux/mm.h>
  28 #include <linux/percpu.h>
  29 #include <linux/slab.h>
  30 #include <linux/capability.h>
  31 #include <linux/blkdev.h>
  32 #include <linux/file.h>
  33 #include <linux/quotaops.h>
  34 #include <linux/highmem.h>
  35 #include <linux/export.h>
  36 #include <linux/backing-dev.h>
  37 #include <linux/writeback.h>
  38 #include <linux/hash.h>
  39 #include <linux/suspend.h>
  40 #include <linux/buffer_head.h>
  41 #include <linux/task_io_accounting_ops.h>
  42 #include <linux/bio.h>
  43 #include <linux/cpu.h>
  44 #include <linux/bitops.h>
  45 #include <linux/mpage.h>
  46 #include <linux/bit_spinlock.h>
  47 #include <linux/pagevec.h>
  48 #include <linux/sched/mm.h>
  49 #include <trace/events/block.h>
  50 
  51 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
  52 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
  53                          enum rw_hint hint, struct writeback_control *wbc);
  54 
  55 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
  56 
  57 inline void touch_buffer(struct buffer_head *bh)
  58 {
  59         trace_block_touch_buffer(bh);
  60         mark_page_accessed(bh->b_page);
  61 }
  62 EXPORT_SYMBOL(touch_buffer);
  63 
  64 void __lock_buffer(struct buffer_head *bh)
  65 {
  66         wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
  67 }
  68 EXPORT_SYMBOL(__lock_buffer);
  69 
  70 void unlock_buffer(struct buffer_head *bh)
  71 {
  72         clear_bit_unlock(BH_Lock, &bh->b_state);
  73         smp_mb__after_atomic();
  74         wake_up_bit(&bh->b_state, BH_Lock);
  75 }
  76 EXPORT_SYMBOL(unlock_buffer);
  77 
  78 /*
  79  * Returns if the page has dirty or writeback buffers. If all the buffers
  80  * are unlocked and clean then the PageDirty information is stale. If
  81  * any of the pages are locked, it is assumed they are locked for IO.
  82  */
  83 void buffer_check_dirty_writeback(struct page *page,
  84                                      bool *dirty, bool *writeback)
  85 {
  86         struct buffer_head *head, *bh;
  87         *dirty = false;
  88         *writeback = false;
  89 
  90         BUG_ON(!PageLocked(page));
  91 
  92         if (!page_has_buffers(page))
  93                 return;
  94 
  95         if (PageWriteback(page))
  96                 *writeback = true;
  97 
  98         head = page_buffers(page);
  99         bh = head;
 100         do {
 101                 if (buffer_locked(bh))
 102                         *writeback = true;
 103 
 104                 if (buffer_dirty(bh))
 105                         *dirty = true;
 106 
 107                 bh = bh->b_this_page;
 108         } while (bh != head);
 109 }
 110 EXPORT_SYMBOL(buffer_check_dirty_writeback);
 111 
 112 /*
 113  * Block until a buffer comes unlocked.  This doesn't stop it
 114  * from becoming locked again - you have to lock it yourself
 115  * if you want to preserve its state.
 116  */
 117 void __wait_on_buffer(struct buffer_head * bh)
 118 {
 119         wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
 120 }
 121 EXPORT_SYMBOL(__wait_on_buffer);
 122 
 123 static void
 124 __clear_page_buffers(struct page *page)
 125 {
 126         ClearPagePrivate(page);
 127         set_page_private(page, 0);
 128         put_page(page);
 129 }
 130 
 131 static void buffer_io_error(struct buffer_head *bh, char *msg)
 132 {
 133         if (!test_bit(BH_Quiet, &bh->b_state))
 134                 printk_ratelimited(KERN_ERR
 135                         "Buffer I/O error on dev %pg, logical block %llu%s\n",
 136                         bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
 137 }
 138 
 139 /*
 140  * End-of-IO handler helper function which does not touch the bh after
 141  * unlocking it.
 142  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
 143  * a race there is benign: unlock_buffer() only use the bh's address for
 144  * hashing after unlocking the buffer, so it doesn't actually touch the bh
 145  * itself.
 146  */
 147 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
 148 {
 149         if (uptodate) {
 150                 set_buffer_uptodate(bh);
 151         } else {
 152                 /* This happens, due to failed read-ahead attempts. */
 153                 clear_buffer_uptodate(bh);
 154         }
 155         unlock_buffer(bh);
 156 }
 157 
 158 /*
 159  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
 160  * unlock the buffer. This is what ll_rw_block uses too.
 161  */
 162 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
 163 {
 164         __end_buffer_read_notouch(bh, uptodate);
 165         put_bh(bh);
 166 }
 167 EXPORT_SYMBOL(end_buffer_read_sync);
 168 
 169 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 170 {
 171         if (uptodate) {
 172                 set_buffer_uptodate(bh);
 173         } else {
 174                 buffer_io_error(bh, ", lost sync page write");
 175                 mark_buffer_write_io_error(bh);
 176                 clear_buffer_uptodate(bh);
 177         }
 178         unlock_buffer(bh);
 179         put_bh(bh);
 180 }
 181 EXPORT_SYMBOL(end_buffer_write_sync);
 182 
 183 /*
 184  * Various filesystems appear to want __find_get_block to be non-blocking.
 185  * But it's the page lock which protects the buffers.  To get around this,
 186  * we get exclusion from try_to_free_buffers with the blockdev mapping's
 187  * private_lock.
 188  *
 189  * Hack idea: for the blockdev mapping, private_lock contention
 190  * may be quite high.  This code could TryLock the page, and if that
 191  * succeeds, there is no need to take private_lock.
 192  */
 193 static struct buffer_head *
 194 __find_get_block_slow(struct block_device *bdev, sector_t block)
 195 {
 196         struct inode *bd_inode = bdev->bd_inode;
 197         struct address_space *bd_mapping = bd_inode->i_mapping;
 198         struct buffer_head *ret = NULL;
 199         pgoff_t index;
 200         struct buffer_head *bh;
 201         struct buffer_head *head;
 202         struct page *page;
 203         int all_mapped = 1;
 204         static DEFINE_RATELIMIT_STATE(last_warned, HZ, 1);
 205 
 206         index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
 207         page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
 208         if (!page)
 209                 goto out;
 210 
 211         spin_lock(&bd_mapping->private_lock);
 212         if (!page_has_buffers(page))
 213                 goto out_unlock;
 214         head = page_buffers(page);
 215         bh = head;
 216         do {
 217                 if (!buffer_mapped(bh))
 218                         all_mapped = 0;
 219                 else if (bh->b_blocknr == block) {
 220                         ret = bh;
 221                         get_bh(bh);
 222                         goto out_unlock;
 223                 }
 224                 bh = bh->b_this_page;
 225         } while (bh != head);
 226 
 227         /* we might be here because some of the buffers on this page are
 228          * not mapped.  This is due to various races between
 229          * file io on the block device and getblk.  It gets dealt with
 230          * elsewhere, don't buffer_error if we had some unmapped buffers
 231          */
 232         ratelimit_set_flags(&last_warned, RATELIMIT_MSG_ON_RELEASE);
 233         if (all_mapped && __ratelimit(&last_warned)) {
 234                 printk("__find_get_block_slow() failed. block=%llu, "
 235                        "b_blocknr=%llu, b_state=0x%08lx, b_size=%zu, "
 236                        "device %pg blocksize: %d\n",
 237                        (unsigned long long)block,
 238                        (unsigned long long)bh->b_blocknr,
 239                        bh->b_state, bh->b_size, bdev,
 240                        1 << bd_inode->i_blkbits);
 241         }
 242 out_unlock:
 243         spin_unlock(&bd_mapping->private_lock);
 244         put_page(page);
 245 out:
 246         return ret;
 247 }
 248 
 249 /*
 250  * I/O completion handler for block_read_full_page() - pages
 251  * which come unlocked at the end of I/O.
 252  */
 253 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
 254 {
 255         unsigned long flags;
 256         struct buffer_head *first;
 257         struct buffer_head *tmp;
 258         struct page *page;
 259         int page_uptodate = 1;
 260 
 261         BUG_ON(!buffer_async_read(bh));
 262 
 263         page = bh->b_page;
 264         if (uptodate) {
 265                 set_buffer_uptodate(bh);
 266         } else {
 267                 clear_buffer_uptodate(bh);
 268                 buffer_io_error(bh, ", async page read");
 269                 SetPageError(page);
 270         }
 271 
 272         /*
 273          * Be _very_ careful from here on. Bad things can happen if
 274          * two buffer heads end IO at almost the same time and both
 275          * decide that the page is now completely done.
 276          */
 277         first = page_buffers(page);
 278         local_irq_save(flags);
 279         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 280         clear_buffer_async_read(bh);
 281         unlock_buffer(bh);
 282         tmp = bh;
 283         do {
 284                 if (!buffer_uptodate(tmp))
 285                         page_uptodate = 0;
 286                 if (buffer_async_read(tmp)) {
 287                         BUG_ON(!buffer_locked(tmp));
 288                         goto still_busy;
 289                 }
 290                 tmp = tmp->b_this_page;
 291         } while (tmp != bh);
 292         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 293         local_irq_restore(flags);
 294 
 295         /*
 296          * If none of the buffers had errors and they are all
 297          * uptodate then we can set the page uptodate.
 298          */
 299         if (page_uptodate && !PageError(page))
 300                 SetPageUptodate(page);
 301         unlock_page(page);
 302         return;
 303 
 304 still_busy:
 305         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 306         local_irq_restore(flags);
 307         return;
 308 }
 309 
 310 /*
 311  * Completion handler for block_write_full_page() - pages which are unlocked
 312  * during I/O, and which have PageWriteback cleared upon I/O completion.
 313  */
 314 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 315 {
 316         unsigned long flags;
 317         struct buffer_head *first;
 318         struct buffer_head *tmp;
 319         struct page *page;
 320 
 321         BUG_ON(!buffer_async_write(bh));
 322 
 323         page = bh->b_page;
 324         if (uptodate) {
 325                 set_buffer_uptodate(bh);
 326         } else {
 327                 buffer_io_error(bh, ", lost async page write");
 328                 mark_buffer_write_io_error(bh);
 329                 clear_buffer_uptodate(bh);
 330                 SetPageError(page);
 331         }
 332 
 333         first = page_buffers(page);
 334         local_irq_save(flags);
 335         bit_spin_lock(BH_Uptodate_Lock, &first->b_state);
 336 
 337         clear_buffer_async_write(bh);
 338         unlock_buffer(bh);
 339         tmp = bh->b_this_page;
 340         while (tmp != bh) {
 341                 if (buffer_async_write(tmp)) {
 342                         BUG_ON(!buffer_locked(tmp));
 343                         goto still_busy;
 344                 }
 345                 tmp = tmp->b_this_page;
 346         }
 347         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 348         local_irq_restore(flags);
 349         end_page_writeback(page);
 350         return;
 351 
 352 still_busy:
 353         bit_spin_unlock(BH_Uptodate_Lock, &first->b_state);
 354         local_irq_restore(flags);
 355         return;
 356 }
 357 EXPORT_SYMBOL(end_buffer_async_write);
 358 
 359 /*
 360  * If a page's buffers are under async readin (end_buffer_async_read
 361  * completion) then there is a possibility that another thread of
 362  * control could lock one of the buffers after it has completed
 363  * but while some of the other buffers have not completed.  This
 364  * locked buffer would confuse end_buffer_async_read() into not unlocking
 365  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
 366  * that this buffer is not under async I/O.
 367  *
 368  * The page comes unlocked when it has no locked buffer_async buffers
 369  * left.
 370  *
 371  * PageLocked prevents anyone starting new async I/O reads any of
 372  * the buffers.
 373  *
 374  * PageWriteback is used to prevent simultaneous writeout of the same
 375  * page.
 376  *
 377  * PageLocked prevents anyone from starting writeback of a page which is
 378  * under read I/O (PageWriteback is only ever set against a locked page).
 379  */
 380 static void mark_buffer_async_read(struct buffer_head *bh)
 381 {
 382         bh->b_end_io = end_buffer_async_read;
 383         set_buffer_async_read(bh);
 384 }
 385 
 386 static void mark_buffer_async_write_endio(struct buffer_head *bh,
 387                                           bh_end_io_t *handler)
 388 {
 389         bh->b_end_io = handler;
 390         set_buffer_async_write(bh);
 391 }
 392 
 393 void mark_buffer_async_write(struct buffer_head *bh)
 394 {
 395         mark_buffer_async_write_endio(bh, end_buffer_async_write);
 396 }
 397 EXPORT_SYMBOL(mark_buffer_async_write);
 398 
 399 
 400 /*
 401  * fs/buffer.c contains helper functions for buffer-backed address space's
 402  * fsync functions.  A common requirement for buffer-based filesystems is
 403  * that certain data from the backing blockdev needs to be written out for
 404  * a successful fsync().  For example, ext2 indirect blocks need to be
 405  * written back and waited upon before fsync() returns.
 406  *
 407  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
 408  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
 409  * management of a list of dependent buffers at ->i_mapping->private_list.
 410  *
 411  * Locking is a little subtle: try_to_free_buffers() will remove buffers
 412  * from their controlling inode's queue when they are being freed.  But
 413  * try_to_free_buffers() will be operating against the *blockdev* mapping
 414  * at the time, not against the S_ISREG file which depends on those buffers.
 415  * So the locking for private_list is via the private_lock in the address_space
 416  * which backs the buffers.  Which is different from the address_space 
 417  * against which the buffers are listed.  So for a particular address_space,
 418  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
 419  * mapping->private_list will always be protected by the backing blockdev's
 420  * ->private_lock.
 421  *
 422  * Which introduces a requirement: all buffers on an address_space's
 423  * ->private_list must be from the same address_space: the blockdev's.
 424  *
 425  * address_spaces which do not place buffers at ->private_list via these
 426  * utility functions are free to use private_lock and private_list for
 427  * whatever they want.  The only requirement is that list_empty(private_list)
 428  * be true at clear_inode() time.
 429  *
 430  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
 431  * filesystems should do that.  invalidate_inode_buffers() should just go
 432  * BUG_ON(!list_empty).
 433  *
 434  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
 435  * take an address_space, not an inode.  And it should be called
 436  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
 437  * queued up.
 438  *
 439  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
 440  * list if it is already on a list.  Because if the buffer is on a list,
 441  * it *must* already be on the right one.  If not, the filesystem is being
 442  * silly.  This will save a ton of locking.  But first we have to ensure
 443  * that buffers are taken *off* the old inode's list when they are freed
 444  * (presumably in truncate).  That requires careful auditing of all
 445  * filesystems (do it inside bforget()).  It could also be done by bringing
 446  * b_inode back.
 447  */
 448 
 449 /*
 450  * The buffer's backing address_space's private_lock must be held
 451  */
 452 static void __remove_assoc_queue(struct buffer_head *bh)
 453 {
 454         list_del_init(&bh->b_assoc_buffers);
 455         WARN_ON(!bh->b_assoc_map);
 456         bh->b_assoc_map = NULL;
 457 }
 458 
 459 int inode_has_buffers(struct inode *inode)
 460 {
 461         return !list_empty(&inode->i_data.private_list);
 462 }
 463 
 464 /*
 465  * osync is designed to support O_SYNC io.  It waits synchronously for
 466  * all already-submitted IO to complete, but does not queue any new
 467  * writes to the disk.
 468  *
 469  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
 470  * you dirty the buffers, and then use osync_inode_buffers to wait for
 471  * completion.  Any other dirty buffers which are not yet queued for
 472  * write will not be flushed to disk by the osync.
 473  */
 474 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
 475 {
 476         struct buffer_head *bh;
 477         struct list_head *p;
 478         int err = 0;
 479 
 480         spin_lock(lock);
 481 repeat:
 482         list_for_each_prev(p, list) {
 483                 bh = BH_ENTRY(p);
 484                 if (buffer_locked(bh)) {
 485                         get_bh(bh);
 486                         spin_unlock(lock);
 487                         wait_on_buffer(bh);
 488                         if (!buffer_uptodate(bh))
 489                                 err = -EIO;
 490                         brelse(bh);
 491                         spin_lock(lock);
 492                         goto repeat;
 493                 }
 494         }
 495         spin_unlock(lock);
 496         return err;
 497 }
 498 
 499 void emergency_thaw_bdev(struct super_block *sb)
 500 {
 501         while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
 502                 printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
 503 }
 504 
 505 /**
 506  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
 507  * @mapping: the mapping which wants those buffers written
 508  *
 509  * Starts I/O against the buffers at mapping->private_list, and waits upon
 510  * that I/O.
 511  *
 512  * Basically, this is a convenience function for fsync().
 513  * @mapping is a file or directory which needs those buffers to be written for
 514  * a successful fsync().
 515  */
 516 int sync_mapping_buffers(struct address_space *mapping)
 517 {
 518         struct address_space *buffer_mapping = mapping->private_data;
 519 
 520         if (buffer_mapping == NULL || list_empty(&mapping->private_list))
 521                 return 0;
 522 
 523         return fsync_buffers_list(&buffer_mapping->private_lock,
 524                                         &mapping->private_list);
 525 }
 526 EXPORT_SYMBOL(sync_mapping_buffers);
 527 
 528 /*
 529  * Called when we've recently written block `bblock', and it is known that
 530  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
 531  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
 532  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
 533  */
 534 void write_boundary_block(struct block_device *bdev,
 535                         sector_t bblock, unsigned blocksize)
 536 {
 537         struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
 538         if (bh) {
 539                 if (buffer_dirty(bh))
 540                         ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
 541                 put_bh(bh);
 542         }
 543 }
 544 
 545 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
 546 {
 547         struct address_space *mapping = inode->i_mapping;
 548         struct address_space *buffer_mapping = bh->b_page->mapping;
 549 
 550         mark_buffer_dirty(bh);
 551         if (!mapping->private_data) {
 552                 mapping->private_data = buffer_mapping;
 553         } else {
 554                 BUG_ON(mapping->private_data != buffer_mapping);
 555         }
 556         if (!bh->b_assoc_map) {
 557                 spin_lock(&buffer_mapping->private_lock);
 558                 list_move_tail(&bh->b_assoc_buffers,
 559                                 &mapping->private_list);
 560                 bh->b_assoc_map = mapping;
 561                 spin_unlock(&buffer_mapping->private_lock);
 562         }
 563 }
 564 EXPORT_SYMBOL(mark_buffer_dirty_inode);
 565 
 566 /*
 567  * Mark the page dirty, and set it dirty in the page cache, and mark the inode
 568  * dirty.
 569  *
 570  * If warn is true, then emit a warning if the page is not uptodate and has
 571  * not been truncated.
 572  *
 573  * The caller must hold lock_page_memcg().
 574  */
 575 void __set_page_dirty(struct page *page, struct address_space *mapping,
 576                              int warn)
 577 {
 578         unsigned long flags;
 579 
 580         xa_lock_irqsave(&mapping->i_pages, flags);
 581         if (page->mapping) {    /* Race with truncate? */
 582                 WARN_ON_ONCE(warn && !PageUptodate(page));
 583                 account_page_dirtied(page, mapping);
 584                 __xa_set_mark(&mapping->i_pages, page_index(page),
 585                                 PAGECACHE_TAG_DIRTY);
 586         }
 587         xa_unlock_irqrestore(&mapping->i_pages, flags);
 588 }
 589 EXPORT_SYMBOL_GPL(__set_page_dirty);
 590 
 591 /*
 592  * Add a page to the dirty page list.
 593  *
 594  * It is a sad fact of life that this function is called from several places
 595  * deeply under spinlocking.  It may not sleep.
 596  *
 597  * If the page has buffers, the uptodate buffers are set dirty, to preserve
 598  * dirty-state coherency between the page and the buffers.  It the page does
 599  * not have buffers then when they are later attached they will all be set
 600  * dirty.
 601  *
 602  * The buffers are dirtied before the page is dirtied.  There's a small race
 603  * window in which a writepage caller may see the page cleanness but not the
 604  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
 605  * before the buffers, a concurrent writepage caller could clear the page dirty
 606  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
 607  * page on the dirty page list.
 608  *
 609  * We use private_lock to lock against try_to_free_buffers while using the
 610  * page's buffer list.  Also use this to protect against clean buffers being
 611  * added to the page after it was set dirty.
 612  *
 613  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
 614  * address_space though.
 615  */
 616 int __set_page_dirty_buffers(struct page *page)
 617 {
 618         int newly_dirty;
 619         struct address_space *mapping = page_mapping(page);
 620 
 621         if (unlikely(!mapping))
 622                 return !TestSetPageDirty(page);
 623 
 624         spin_lock(&mapping->private_lock);
 625         if (page_has_buffers(page)) {
 626                 struct buffer_head *head = page_buffers(page);
 627                 struct buffer_head *bh = head;
 628 
 629                 do {
 630                         set_buffer_dirty(bh);
 631                         bh = bh->b_this_page;
 632                 } while (bh != head);
 633         }
 634         /*
 635          * Lock out page->mem_cgroup migration to keep PageDirty
 636          * synchronized with per-memcg dirty page counters.
 637          */
 638         lock_page_memcg(page);
 639         newly_dirty = !TestSetPageDirty(page);
 640         spin_unlock(&mapping->private_lock);
 641 
 642         if (newly_dirty)
 643                 __set_page_dirty(page, mapping, 1);
 644 
 645         unlock_page_memcg(page);
 646 
 647         if (newly_dirty)
 648                 __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 649 
 650         return newly_dirty;
 651 }
 652 EXPORT_SYMBOL(__set_page_dirty_buffers);
 653 
 654 /*
 655  * Write out and wait upon a list of buffers.
 656  *
 657  * We have conflicting pressures: we want to make sure that all
 658  * initially dirty buffers get waited on, but that any subsequently
 659  * dirtied buffers don't.  After all, we don't want fsync to last
 660  * forever if somebody is actively writing to the file.
 661  *
 662  * Do this in two main stages: first we copy dirty buffers to a
 663  * temporary inode list, queueing the writes as we go.  Then we clean
 664  * up, waiting for those writes to complete.
 665  * 
 666  * During this second stage, any subsequent updates to the file may end
 667  * up refiling the buffer on the original inode's dirty list again, so
 668  * there is a chance we will end up with a buffer queued for write but
 669  * not yet completed on that list.  So, as a final cleanup we go through
 670  * the osync code to catch these locked, dirty buffers without requeuing
 671  * any newly dirty buffers for write.
 672  */
 673 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
 674 {
 675         struct buffer_head *bh;
 676         struct list_head tmp;
 677         struct address_space *mapping;
 678         int err = 0, err2;
 679         struct blk_plug plug;
 680 
 681         INIT_LIST_HEAD(&tmp);
 682         blk_start_plug(&plug);
 683 
 684         spin_lock(lock);
 685         while (!list_empty(list)) {
 686                 bh = BH_ENTRY(list->next);
 687                 mapping = bh->b_assoc_map;
 688                 __remove_assoc_queue(bh);
 689                 /* Avoid race with mark_buffer_dirty_inode() which does
 690                  * a lockless check and we rely on seeing the dirty bit */
 691                 smp_mb();
 692                 if (buffer_dirty(bh) || buffer_locked(bh)) {
 693                         list_add(&bh->b_assoc_buffers, &tmp);
 694                         bh->b_assoc_map = mapping;
 695                         if (buffer_dirty(bh)) {
 696                                 get_bh(bh);
 697                                 spin_unlock(lock);
 698                                 /*
 699                                  * Ensure any pending I/O completes so that
 700                                  * write_dirty_buffer() actually writes the
 701                                  * current contents - it is a noop if I/O is
 702                                  * still in flight on potentially older
 703                                  * contents.
 704                                  */
 705                                 write_dirty_buffer(bh, REQ_SYNC);
 706 
 707                                 /*
 708                                  * Kick off IO for the previous mapping. Note
 709                                  * that we will not run the very last mapping,
 710                                  * wait_on_buffer() will do that for us
 711                                  * through sync_buffer().
 712                                  */
 713                                 brelse(bh);
 714                                 spin_lock(lock);
 715                         }
 716                 }
 717         }
 718 
 719         spin_unlock(lock);
 720         blk_finish_plug(&plug);
 721         spin_lock(lock);
 722 
 723         while (!list_empty(&tmp)) {
 724                 bh = BH_ENTRY(tmp.prev);
 725                 get_bh(bh);
 726                 mapping = bh->b_assoc_map;
 727                 __remove_assoc_queue(bh);
 728                 /* Avoid race with mark_buffer_dirty_inode() which does
 729                  * a lockless check and we rely on seeing the dirty bit */
 730                 smp_mb();
 731                 if (buffer_dirty(bh)) {
 732                         list_add(&bh->b_assoc_buffers,
 733                                  &mapping->private_list);
 734                         bh->b_assoc_map = mapping;
 735                 }
 736                 spin_unlock(lock);
 737                 wait_on_buffer(bh);
 738                 if (!buffer_uptodate(bh))
 739                         err = -EIO;
 740                 brelse(bh);
 741                 spin_lock(lock);
 742         }
 743         
 744         spin_unlock(lock);
 745         err2 = osync_buffers_list(lock, list);
 746         if (err)
 747                 return err;
 748         else
 749                 return err2;
 750 }
 751 
 752 /*
 753  * Invalidate any and all dirty buffers on a given inode.  We are
 754  * probably unmounting the fs, but that doesn't mean we have already
 755  * done a sync().  Just drop the buffers from the inode list.
 756  *
 757  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
 758  * assumes that all the buffers are against the blockdev.  Not true
 759  * for reiserfs.
 760  */
 761 void invalidate_inode_buffers(struct inode *inode)
 762 {
 763         if (inode_has_buffers(inode)) {
 764                 struct address_space *mapping = &inode->i_data;
 765                 struct list_head *list = &mapping->private_list;
 766                 struct address_space *buffer_mapping = mapping->private_data;
 767 
 768                 spin_lock(&buffer_mapping->private_lock);
 769                 while (!list_empty(list))
 770                         __remove_assoc_queue(BH_ENTRY(list->next));
 771                 spin_unlock(&buffer_mapping->private_lock);
 772         }
 773 }
 774 EXPORT_SYMBOL(invalidate_inode_buffers);
 775 
 776 /*
 777  * Remove any clean buffers from the inode's buffer list.  This is called
 778  * when we're trying to free the inode itself.  Those buffers can pin it.
 779  *
 780  * Returns true if all buffers were removed.
 781  */
 782 int remove_inode_buffers(struct inode *inode)
 783 {
 784         int ret = 1;
 785 
 786         if (inode_has_buffers(inode)) {
 787                 struct address_space *mapping = &inode->i_data;
 788                 struct list_head *list = &mapping->private_list;
 789                 struct address_space *buffer_mapping = mapping->private_data;
 790 
 791                 spin_lock(&buffer_mapping->private_lock);
 792                 while (!list_empty(list)) {
 793                         struct buffer_head *bh = BH_ENTRY(list->next);
 794                         if (buffer_dirty(bh)) {
 795                                 ret = 0;
 796                                 break;
 797                         }
 798                         __remove_assoc_queue(bh);
 799                 }
 800                 spin_unlock(&buffer_mapping->private_lock);
 801         }
 802         return ret;
 803 }
 804 
 805 /*
 806  * Create the appropriate buffers when given a page for data area and
 807  * the size of each buffer.. Use the bh->b_this_page linked list to
 808  * follow the buffers created.  Return NULL if unable to create more
 809  * buffers.
 810  *
 811  * The retry flag is used to differentiate async IO (paging, swapping)
 812  * which may not fail from ordinary buffer allocations.
 813  */
 814 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 815                 bool retry)
 816 {
 817         struct buffer_head *bh, *head;
 818         gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
 819         long offset;
 820         struct mem_cgroup *memcg;
 821 
 822         if (retry)
 823                 gfp |= __GFP_NOFAIL;
 824 
 825         memcg = get_mem_cgroup_from_page(page);
 826         memalloc_use_memcg(memcg);
 827 
 828         head = NULL;
 829         offset = PAGE_SIZE;
 830         while ((offset -= size) >= 0) {
 831                 bh = alloc_buffer_head(gfp);
 832                 if (!bh)
 833                         goto no_grow;
 834 
 835                 bh->b_this_page = head;
 836                 bh->b_blocknr = -1;
 837                 head = bh;
 838 
 839                 bh->b_size = size;
 840 
 841                 /* Link the buffer to its page */
 842                 set_bh_page(bh, page, offset);
 843         }
 844 out:
 845         memalloc_unuse_memcg();
 846         mem_cgroup_put(memcg);
 847         return head;
 848 /*
 849  * In case anything failed, we just free everything we got.
 850  */
 851 no_grow:
 852         if (head) {
 853                 do {
 854                         bh = head;
 855                         head = head->b_this_page;
 856                         free_buffer_head(bh);
 857                 } while (head);
 858         }
 859 
 860         goto out;
 861 }
 862 EXPORT_SYMBOL_GPL(alloc_page_buffers);
 863 
 864 static inline void
 865 link_dev_buffers(struct page *page, struct buffer_head *head)
 866 {
 867         struct buffer_head *bh, *tail;
 868 
 869         bh = head;
 870         do {
 871                 tail = bh;
 872                 bh = bh->b_this_page;
 873         } while (bh);
 874         tail->b_this_page = head;
 875         attach_page_buffers(page, head);
 876 }
 877 
 878 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 879 {
 880         sector_t retval = ~((sector_t)0);
 881         loff_t sz = i_size_read(bdev->bd_inode);
 882 
 883         if (sz) {
 884                 unsigned int sizebits = blksize_bits(size);
 885                 retval = (sz >> sizebits);
 886         }
 887         return retval;
 888 }
 889 
 890 /*
 891  * Initialise the state of a blockdev page's buffers.
 892  */ 
 893 static sector_t
 894 init_page_buffers(struct page *page, struct block_device *bdev,
 895                         sector_t block, int size)
 896 {
 897         struct buffer_head *head = page_buffers(page);
 898         struct buffer_head *bh = head;
 899         int uptodate = PageUptodate(page);
 900         sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode), size);
 901 
 902         do {
 903                 if (!buffer_mapped(bh)) {
 904                         bh->b_end_io = NULL;
 905                         bh->b_private = NULL;
 906                         bh->b_bdev = bdev;
 907                         bh->b_blocknr = block;
 908                         if (uptodate)
 909                                 set_buffer_uptodate(bh);
 910                         if (block < end_block)
 911                                 set_buffer_mapped(bh);
 912                 }
 913                 block++;
 914                 bh = bh->b_this_page;
 915         } while (bh != head);
 916 
 917         /*
 918          * Caller needs to validate requested block against end of device.
 919          */
 920         return end_block;
 921 }
 922 
 923 /*
 924  * Create the page-cache page that contains the requested block.
 925  *
 926  * This is used purely for blockdev mappings.
 927  */
 928 static int
 929 grow_dev_page(struct block_device *bdev, sector_t block,
 930               pgoff_t index, int size, int sizebits, gfp_t gfp)
 931 {
 932         struct inode *inode = bdev->bd_inode;
 933         struct page *page;
 934         struct buffer_head *bh;
 935         sector_t end_block;
 936         int ret = 0;            /* Will call free_more_memory() */
 937         gfp_t gfp_mask;
 938 
 939         gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
 940 
 941         /*
 942          * XXX: __getblk_slow() can not really deal with failure and
 943          * will endlessly loop on improvised global reclaim.  Prefer
 944          * looping in the allocator rather than here, at least that
 945          * code knows what it's doing.
 946          */
 947         gfp_mask |= __GFP_NOFAIL;
 948 
 949         page = find_or_create_page(inode->i_mapping, index, gfp_mask);
 950 
 951         BUG_ON(!PageLocked(page));
 952 
 953         if (page_has_buffers(page)) {
 954                 bh = page_buffers(page);
 955                 if (bh->b_size == size) {
 956                         end_block = init_page_buffers(page, bdev,
 957                                                 (sector_t)index << sizebits,
 958                                                 size);
 959                         goto done;
 960                 }
 961                 if (!try_to_free_buffers(page))
 962                         goto failed;
 963         }
 964 
 965         /*
 966          * Allocate some buffers for this page
 967          */
 968         bh = alloc_page_buffers(page, size, true);
 969 
 970         /*
 971          * Link the page to the buffers and initialise them.  Take the
 972          * lock to be atomic wrt __find_get_block(), which does not
 973          * run under the page lock.
 974          */
 975         spin_lock(&inode->i_mapping->private_lock);
 976         link_dev_buffers(page, bh);
 977         end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
 978                         size);
 979         spin_unlock(&inode->i_mapping->private_lock);
 980 done:
 981         ret = (block < end_block) ? 1 : -ENXIO;
 982 failed:
 983         unlock_page(page);
 984         put_page(page);
 985         return ret;
 986 }
 987 
 988 /*
 989  * Create buffers for the specified block device block's page.  If
 990  * that page was dirty, the buffers are set dirty also.
 991  */
 992 static int
 993 grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
 994 {
 995         pgoff_t index;
 996         int sizebits;
 997 
 998         sizebits = -1;
 999         do {
1000                 sizebits++;
1001         } while ((size << sizebits) < PAGE_SIZE);
1002 
1003         index = block >> sizebits;
1004 
1005         /*
1006          * Check for a block which wants to lie outside our maximum possible
1007          * pagecache index.  (this comparison is done using sector_t types).
1008          */
1009         if (unlikely(index != block >> sizebits)) {
1010                 printk(KERN_ERR "%s: requested out-of-range block %llu for "
1011                         "device %pg\n",
1012                         __func__, (unsigned long long)block,
1013                         bdev);
1014                 return -EIO;
1015         }
1016 
1017         /* Create a page with the proper size buffers.. */
1018         return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1019 }
1020 
1021 static struct buffer_head *
1022 __getblk_slow(struct block_device *bdev, sector_t block,
1023              unsigned size, gfp_t gfp)
1024 {
1025         /* Size must be multiple of hard sectorsize */
1026         if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1027                         (size < 512 || size > PAGE_SIZE))) {
1028                 printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1029                                         size);
1030                 printk(KERN_ERR "logical block size: %d\n",
1031                                         bdev_logical_block_size(bdev));
1032 
1033                 dump_stack();
1034                 return NULL;
1035         }
1036 
1037         for (;;) {
1038                 struct buffer_head *bh;
1039                 int ret;
1040 
1041                 bh = __find_get_block(bdev, block, size);
1042                 if (bh)
1043                         return bh;
1044 
1045                 ret = grow_buffers(bdev, block, size, gfp);
1046                 if (ret < 0)
1047                         return NULL;
1048         }
1049 }
1050 
1051 /*
1052  * The relationship between dirty buffers and dirty pages:
1053  *
1054  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1055  * the page is tagged dirty in the page cache.
1056  *
1057  * At all times, the dirtiness of the buffers represents the dirtiness of
1058  * subsections of the page.  If the page has buffers, the page dirty bit is
1059  * merely a hint about the true dirty state.
1060  *
1061  * When a page is set dirty in its entirety, all its buffers are marked dirty
1062  * (if the page has buffers).
1063  *
1064  * When a buffer is marked dirty, its page is dirtied, but the page's other
1065  * buffers are not.
1066  *
1067  * Also.  When blockdev buffers are explicitly read with bread(), they
1068  * individually become uptodate.  But their backing page remains not
1069  * uptodate - even if all of its buffers are uptodate.  A subsequent
1070  * block_read_full_page() against that page will discover all the uptodate
1071  * buffers, will set the page uptodate and will perform no I/O.
1072  */
1073 
1074 /**
1075  * mark_buffer_dirty - mark a buffer_head as needing writeout
1076  * @bh: the buffer_head to mark dirty
1077  *
1078  * mark_buffer_dirty() will set the dirty bit against the buffer, then set
1079  * its backing page dirty, then tag the page as dirty in the page cache
1080  * and then attach the address_space's inode to its superblock's dirty
1081  * inode list.
1082  *
1083  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1084  * i_pages lock and mapping->host->i_lock.
1085  */
1086 void mark_buffer_dirty(struct buffer_head *bh)
1087 {
1088         WARN_ON_ONCE(!buffer_uptodate(bh));
1089 
1090         trace_block_dirty_buffer(bh);
1091 
1092         /*
1093          * Very *carefully* optimize the it-is-already-dirty case.
1094          *
1095          * Don't let the final "is it dirty" escape to before we
1096          * perhaps modified the buffer.
1097          */
1098         if (buffer_dirty(bh)) {
1099                 smp_mb();
1100                 if (buffer_dirty(bh))
1101                         return;
1102         }
1103 
1104         if (!test_set_buffer_dirty(bh)) {
1105                 struct page *page = bh->b_page;
1106                 struct address_space *mapping = NULL;
1107 
1108                 lock_page_memcg(page);
1109                 if (!TestSetPageDirty(page)) {
1110                         mapping = page_mapping(page);
1111                         if (mapping)
1112                                 __set_page_dirty(page, mapping, 0);
1113                 }
1114                 unlock_page_memcg(page);
1115                 if (mapping)
1116                         __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1117         }
1118 }
1119 EXPORT_SYMBOL(mark_buffer_dirty);
1120 
1121 void mark_buffer_write_io_error(struct buffer_head *bh)
1122 {
1123         set_buffer_write_io_error(bh);
1124         /* FIXME: do we need to set this in both places? */
1125         if (bh->b_page && bh->b_page->mapping)
1126                 mapping_set_error(bh->b_page->mapping, -EIO);
1127         if (bh->b_assoc_map)
1128                 mapping_set_error(bh->b_assoc_map, -EIO);
1129 }
1130 EXPORT_SYMBOL(mark_buffer_write_io_error);
1131 
1132 /*
1133  * Decrement a buffer_head's reference count.  If all buffers against a page
1134  * have zero reference count, are clean and unlocked, and if the page is clean
1135  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1136  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1137  * a page but it ends up not being freed, and buffers may later be reattached).
1138  */
1139 void __brelse(struct buffer_head * buf)
1140 {
1141         if (atomic_read(&buf->b_count)) {
1142                 put_bh(buf);
1143                 return;
1144         }
1145         WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1146 }
1147 EXPORT_SYMBOL(__brelse);
1148 
1149 /*
1150  * bforget() is like brelse(), except it discards any
1151  * potentially dirty data.
1152  */
1153 void __bforget(struct buffer_head *bh)
1154 {
1155         clear_buffer_dirty(bh);
1156         if (bh->b_assoc_map) {
1157                 struct address_space *buffer_mapping = bh->b_page->mapping;
1158 
1159                 spin_lock(&buffer_mapping->private_lock);
1160                 list_del_init(&bh->b_assoc_buffers);
1161                 bh->b_assoc_map = NULL;
1162                 spin_unlock(&buffer_mapping->private_lock);
1163         }
1164         __brelse(bh);
1165 }
1166 EXPORT_SYMBOL(__bforget);
1167 
1168 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1169 {
1170         lock_buffer(bh);
1171         if (buffer_uptodate(bh)) {
1172                 unlock_buffer(bh);
1173                 return bh;
1174         } else {
1175                 get_bh(bh);
1176                 bh->b_end_io = end_buffer_read_sync;
1177                 submit_bh(REQ_OP_READ, 0, bh);
1178                 wait_on_buffer(bh);
1179                 if (buffer_uptodate(bh))
1180                         return bh;
1181         }
1182         brelse(bh);
1183         return NULL;
1184 }
1185 
1186 /*
1187  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1188  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1189  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1190  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1191  * CPU's LRUs at the same time.
1192  *
1193  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1194  * sb_find_get_block().
1195  *
1196  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1197  * a local interrupt disable for that.
1198  */
1199 
1200 #define BH_LRU_SIZE     16
1201 
1202 struct bh_lru {
1203         struct buffer_head *bhs[BH_LRU_SIZE];
1204 };
1205 
1206 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1207 
1208 #ifdef CONFIG_SMP
1209 #define bh_lru_lock()   local_irq_disable()
1210 #define bh_lru_unlock() local_irq_enable()
1211 #else
1212 #define bh_lru_lock()   preempt_disable()
1213 #define bh_lru_unlock() preempt_enable()
1214 #endif
1215 
1216 static inline void check_irqs_on(void)
1217 {
1218 #ifdef irqs_disabled
1219         BUG_ON(irqs_disabled());
1220 #endif
1221 }
1222 
1223 /*
1224  * Install a buffer_head into this cpu's LRU.  If not already in the LRU, it is
1225  * inserted at the front, and the buffer_head at the back if any is evicted.
1226  * Or, if already in the LRU it is moved to the front.
1227  */
1228 static void bh_lru_install(struct buffer_head *bh)
1229 {
1230         struct buffer_head *evictee = bh;
1231         struct bh_lru *b;
1232         int i;
1233 
1234         check_irqs_on();
1235         bh_lru_lock();
1236 
1237         b = this_cpu_ptr(&bh_lrus);
1238         for (i = 0; i < BH_LRU_SIZE; i++) {
1239                 swap(evictee, b->bhs[i]);
1240                 if (evictee == bh) {
1241                         bh_lru_unlock();
1242                         return;
1243                 }
1244         }
1245 
1246         get_bh(bh);
1247         bh_lru_unlock();
1248         brelse(evictee);
1249 }
1250 
1251 /*
1252  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1253  */
1254 static struct buffer_head *
1255 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1256 {
1257         struct buffer_head *ret = NULL;
1258         unsigned int i;
1259 
1260         check_irqs_on();
1261         bh_lru_lock();
1262         for (i = 0; i < BH_LRU_SIZE; i++) {
1263                 struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1264 
1265                 if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1266                     bh->b_size == size) {
1267                         if (i) {
1268                                 while (i) {
1269                                         __this_cpu_write(bh_lrus.bhs[i],
1270                                                 __this_cpu_read(bh_lrus.bhs[i - 1]));
1271                                         i--;
1272                                 }
1273                                 __this_cpu_write(bh_lrus.bhs[0], bh);
1274                         }
1275                         get_bh(bh);
1276                         ret = bh;
1277                         break;
1278                 }
1279         }
1280         bh_lru_unlock();
1281         return ret;
1282 }
1283 
1284 /*
1285  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1286  * it in the LRU and mark it as accessed.  If it is not present then return
1287  * NULL
1288  */
1289 struct buffer_head *
1290 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1291 {
1292         struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1293 
1294         if (bh == NULL) {
1295                 /* __find_get_block_slow will mark the page accessed */
1296                 bh = __find_get_block_slow(bdev, block);
1297                 if (bh)
1298                         bh_lru_install(bh);
1299         } else
1300                 touch_buffer(bh);
1301 
1302         return bh;
1303 }
1304 EXPORT_SYMBOL(__find_get_block);
1305 
1306 /*
1307  * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1308  * which corresponds to the passed block_device, block and size. The
1309  * returned buffer has its reference count incremented.
1310  *
1311  * __getblk_gfp() will lock up the machine if grow_dev_page's
1312  * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
1313  */
1314 struct buffer_head *
1315 __getblk_gfp(struct block_device *bdev, sector_t block,
1316              unsigned size, gfp_t gfp)
1317 {
1318         struct buffer_head *bh = __find_get_block(bdev, block, size);
1319 
1320         might_sleep();
1321         if (bh == NULL)
1322                 bh = __getblk_slow(bdev, block, size, gfp);
1323         return bh;
1324 }
1325 EXPORT_SYMBOL(__getblk_gfp);
1326 
1327 /*
1328  * Do async read-ahead on a buffer..
1329  */
1330 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1331 {
1332         struct buffer_head *bh = __getblk(bdev, block, size);
1333         if (likely(bh)) {
1334                 ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1335                 brelse(bh);
1336         }
1337 }
1338 EXPORT_SYMBOL(__breadahead);
1339 
1340 void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
1341                       gfp_t gfp)
1342 {
1343         struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1344         if (likely(bh)) {
1345                 ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1346                 brelse(bh);
1347         }
1348 }
1349 EXPORT_SYMBOL(__breadahead_gfp);
1350 
1351 /**
1352  *  __bread_gfp() - reads a specified block and returns the bh
1353  *  @bdev: the block_device to read from
1354  *  @block: number of block
1355  *  @size: size (in bytes) to read
1356  *  @gfp: page allocation flag
1357  *
1358  *  Reads a specified block, and returns buffer head that contains it.
1359  *  The page cache can be allocated from non-movable area
1360  *  not to prevent page migration if you set gfp to zero.
1361  *  It returns NULL if the block was unreadable.
1362  */
1363 struct buffer_head *
1364 __bread_gfp(struct block_device *bdev, sector_t block,
1365                    unsigned size, gfp_t gfp)
1366 {
1367         struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1368 
1369         if (likely(bh) && !buffer_uptodate(bh))
1370                 bh = __bread_slow(bh);
1371         return bh;
1372 }
1373 EXPORT_SYMBOL(__bread_gfp);
1374 
1375 /*
1376  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1377  * This doesn't race because it runs in each cpu either in irq
1378  * or with preempt disabled.
1379  */
1380 static void invalidate_bh_lru(void *arg)
1381 {
1382         struct bh_lru *b = &get_cpu_var(bh_lrus);
1383         int i;
1384 
1385         for (i = 0; i < BH_LRU_SIZE; i++) {
1386                 brelse(b->bhs[i]);
1387                 b->bhs[i] = NULL;
1388         }
1389         put_cpu_var(bh_lrus);
1390 }
1391 
1392 static bool has_bh_in_lru(int cpu, void *dummy)
1393 {
1394         struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1395         int i;
1396         
1397         for (i = 0; i < BH_LRU_SIZE; i++) {
1398                 if (b->bhs[i])
1399                         return 1;
1400         }
1401 
1402         return 0;
1403 }
1404 
1405 void invalidate_bh_lrus(void)
1406 {
1407         on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL);
1408 }
1409 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1410 
1411 void set_bh_page(struct buffer_head *bh,
1412                 struct page *page, unsigned long offset)
1413 {
1414         bh->b_page = page;
1415         BUG_ON(offset >= PAGE_SIZE);
1416         if (PageHighMem(page))
1417                 /*
1418                  * This catches illegal uses and preserves the offset:
1419                  */
1420                 bh->b_data = (char *)(0 + offset);
1421         else
1422                 bh->b_data = page_address(page) + offset;
1423 }
1424 EXPORT_SYMBOL(set_bh_page);
1425 
1426 /*
1427  * Called when truncating a buffer on a page completely.
1428  */
1429 
1430 /* Bits that are cleared during an invalidate */
1431 #define BUFFER_FLAGS_DISCARD \
1432         (1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1433          1 << BH_Delay | 1 << BH_Unwritten)
1434 
1435 static void discard_buffer(struct buffer_head * bh)
1436 {
1437         unsigned long b_state, b_state_old;
1438 
1439         lock_buffer(bh);
1440         clear_buffer_dirty(bh);
1441         bh->b_bdev = NULL;
1442         b_state = bh->b_state;
1443         for (;;) {
1444                 b_state_old = cmpxchg(&bh->b_state, b_state,
1445                                       (b_state & ~BUFFER_FLAGS_DISCARD));
1446                 if (b_state_old == b_state)
1447                         break;
1448                 b_state = b_state_old;
1449         }
1450         unlock_buffer(bh);
1451 }
1452 
1453 /**
1454  * block_invalidatepage - invalidate part or all of a buffer-backed page
1455  *
1456  * @page: the page which is affected
1457  * @offset: start of the range to invalidate
1458  * @length: length of the range to invalidate
1459  *
1460  * block_invalidatepage() is called when all or part of the page has become
1461  * invalidated by a truncate operation.
1462  *
1463  * block_invalidatepage() does not have to release all buffers, but it must
1464  * ensure that no dirty buffer is left outside @offset and that no I/O
1465  * is underway against any of the blocks which are outside the truncation
1466  * point.  Because the caller is about to free (and possibly reuse) those
1467  * blocks on-disk.
1468  */
1469 void block_invalidatepage(struct page *page, unsigned int offset,
1470                           unsigned int length)
1471 {
1472         struct buffer_head *head, *bh, *next;
1473         unsigned int curr_off = 0;
1474         unsigned int stop = length + offset;
1475 
1476         BUG_ON(!PageLocked(page));
1477         if (!page_has_buffers(page))
1478                 goto out;
1479 
1480         /*
1481          * Check for overflow
1482          */
1483         BUG_ON(stop > PAGE_SIZE || stop < length);
1484 
1485         head = page_buffers(page);
1486         bh = head;
1487         do {
1488                 unsigned int next_off = curr_off + bh->b_size;
1489                 next = bh->b_this_page;
1490 
1491                 /*
1492                  * Are we still fully in range ?
1493                  */
1494                 if (next_off > stop)
1495                         goto out;
1496 
1497                 /*
1498                  * is this block fully invalidated?
1499                  */
1500                 if (offset <= curr_off)
1501                         discard_buffer(bh);
1502                 curr_off = next_off;
1503                 bh = next;
1504         } while (bh != head);
1505 
1506         /*
1507          * We release buffers only if the entire page is being invalidated.
1508          * The get_block cached value has been unconditionally invalidated,
1509          * so real IO is not possible anymore.
1510          */
1511         if (length == PAGE_SIZE)
1512                 try_to_release_page(page, 0);
1513 out:
1514         return;
1515 }
1516 EXPORT_SYMBOL(block_invalidatepage);
1517 
1518 
1519 /*
1520  * We attach and possibly dirty the buffers atomically wrt
1521  * __set_page_dirty_buffers() via private_lock.  try_to_free_buffers
1522  * is already excluded via the page lock.
1523  */
1524 void create_empty_buffers(struct page *page,
1525                         unsigned long blocksize, unsigned long b_state)
1526 {
1527         struct buffer_head *bh, *head, *tail;
1528 
1529         head = alloc_page_buffers(page, blocksize, true);
1530         bh = head;
1531         do {
1532                 bh->b_state |= b_state;
1533                 tail = bh;
1534                 bh = bh->b_this_page;
1535         } while (bh);
1536         tail->b_this_page = head;
1537 
1538         spin_lock(&page->mapping->private_lock);
1539         if (PageUptodate(page) || PageDirty(page)) {
1540                 bh = head;
1541                 do {
1542                         if (PageDirty(page))
1543                                 set_buffer_dirty(bh);
1544                         if (PageUptodate(page))
1545                                 set_buffer_uptodate(bh);
1546                         bh = bh->b_this_page;
1547                 } while (bh != head);
1548         }
1549         attach_page_buffers(page, head);
1550         spin_unlock(&page->mapping->private_lock);
1551 }
1552 EXPORT_SYMBOL(create_empty_buffers);
1553 
1554 /**
1555  * clean_bdev_aliases: clean a range of buffers in block device
1556  * @bdev: Block device to clean buffers in
1557  * @block: Start of a range of blocks to clean
1558  * @len: Number of blocks to clean
1559  *
1560  * We are taking a range of blocks for data and we don't want writeback of any
1561  * buffer-cache aliases starting from return from this function and until the
1562  * moment when something will explicitly mark the buffer dirty (hopefully that
1563  * will not happen until we will free that block ;-) We don't even need to mark
1564  * it not-uptodate - nobody can expect anything from a newly allocated buffer
1565  * anyway. We used to use unmap_buffer() for such invalidation, but that was
1566  * wrong. We definitely don't want to mark the alias unmapped, for example - it
1567  * would confuse anyone who might pick it with bread() afterwards...
1568  *
1569  * Also..  Note that bforget() doesn't lock the buffer.  So there can be
1570  * writeout I/O going on against recently-freed buffers.  We don't wait on that
1571  * I/O in bforget() - it's more efficient to wait on the I/O only if we really
1572  * need to.  That happens here.
1573  */
1574 void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
1575 {
1576         struct inode *bd_inode = bdev->bd_inode;
1577         struct address_space *bd_mapping = bd_inode->i_mapping;
1578         struct pagevec pvec;
1579         pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
1580         pgoff_t end;
1581         int i, count;
1582         struct buffer_head *bh;
1583         struct buffer_head *head;
1584 
1585         end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
1586         pagevec_init(&pvec);
1587         while (pagevec_lookup_range(&pvec, bd_mapping, &index, end)) {
1588                 count = pagevec_count(&pvec);
1589                 for (i = 0; i < count; i++) {
1590                         struct page *page = pvec.pages[i];
1591 
1592                         if (!page_has_buffers(page))
1593                                 continue;
1594                         /*
1595                          * We use page lock instead of bd_mapping->private_lock
1596                          * to pin buffers here since we can afford to sleep and
1597                          * it scales better than a global spinlock lock.
1598                          */
1599                         lock_page(page);
1600                         /* Recheck when the page is locked which pins bhs */
1601                         if (!page_has_buffers(page))
1602                                 goto unlock_page;
1603                         head = page_buffers(page);
1604                         bh = head;
1605                         do {
1606                                 if (!buffer_mapped(bh) || (bh->b_blocknr < block))
1607                                         goto next;
1608                                 if (bh->b_blocknr >= block + len)
1609                                         break;
1610                                 clear_buffer_dirty(bh);
1611                                 wait_on_buffer(bh);
1612                                 clear_buffer_req(bh);
1613 next:
1614                                 bh = bh->b_this_page;
1615                         } while (bh != head);
1616 unlock_page:
1617                         unlock_page(page);
1618                 }
1619                 pagevec_release(&pvec);
1620                 cond_resched();
1621                 /* End of range already reached? */
1622                 if (index > end || !index)
1623                         break;
1624         }
1625 }
1626 EXPORT_SYMBOL(clean_bdev_aliases);
1627 
1628 /*
1629  * Size is a power-of-two in the range 512..PAGE_SIZE,
1630  * and the case we care about most is PAGE_SIZE.
1631  *
1632  * So this *could* possibly be written with those
1633  * constraints in mind (relevant mostly if some
1634  * architecture has a slow bit-scan instruction)
1635  */
1636 static inline int block_size_bits(unsigned int blocksize)
1637 {
1638         return ilog2(blocksize);
1639 }
1640 
1641 static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1642 {
1643         BUG_ON(!PageLocked(page));
1644 
1645         if (!page_has_buffers(page))
1646                 create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
1647                                      b_state);
1648         return page_buffers(page);
1649 }
1650 
1651 /*
1652  * NOTE! All mapped/uptodate combinations are valid:
1653  *
1654  *      Mapped  Uptodate        Meaning
1655  *
1656  *      No      No              "unknown" - must do get_block()
1657  *      No      Yes             "hole" - zero-filled
1658  *      Yes     No              "allocated" - allocated on disk, not read in
1659  *      Yes     Yes             "valid" - allocated and up-to-date in memory.
1660  *
1661  * "Dirty" is valid only with the last case (mapped+uptodate).
1662  */
1663 
1664 /*
1665  * While block_write_full_page is writing back the dirty buffers under
1666  * the page lock, whoever dirtied the buffers may decide to clean them
1667  * again at any time.  We handle that by only looking at the buffer
1668  * state inside lock_buffer().
1669  *
1670  * If block_write_full_page() is called for regular writeback
1671  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1672  * locked buffer.   This only can happen if someone has written the buffer
1673  * directly, with submit_bh().  At the address_space level PageWriteback
1674  * prevents this contention from occurring.
1675  *
1676  * If block_write_full_page() is called with wbc->sync_mode ==
1677  * WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
1678  * causes the writes to be flagged as synchronous writes.
1679  */
1680 int __block_write_full_page(struct inode *inode, struct page *page,
1681                         get_block_t *get_block, struct writeback_control *wbc,
1682                         bh_end_io_t *handler)
1683 {
1684         int err;
1685         sector_t block;
1686         sector_t last_block;
1687         struct buffer_head *bh, *head;
1688         unsigned int blocksize, bbits;
1689         int nr_underway = 0;
1690         int write_flags = wbc_to_write_flags(wbc);
1691 
1692         head = create_page_buffers(page, inode,
1693                                         (1 << BH_Dirty)|(1 << BH_Uptodate));
1694 
1695         /*
1696          * Be very careful.  We have no exclusion from __set_page_dirty_buffers
1697          * here, and the (potentially unmapped) buffers may become dirty at
1698          * any time.  If a buffer becomes dirty here after we've inspected it
1699          * then we just miss that fact, and the page stays dirty.
1700          *
1701          * Buffers outside i_size may be dirtied by __set_page_dirty_buffers;
1702          * handle that here by just cleaning them.
1703          */
1704 
1705         bh = head;
1706         blocksize = bh->b_size;
1707         bbits = block_size_bits(blocksize);
1708 
1709         block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1710         last_block = (i_size_read(inode) - 1) >> bbits;
1711 
1712         /*
1713          * Get all the dirty buffers mapped to disk addresses and
1714          * handle any aliases from the underlying blockdev's mapping.
1715          */
1716         do {
1717                 if (block > last_block) {
1718                         /*
1719                          * mapped buffers outside i_size will occur, because
1720                          * this page can be outside i_size when there is a
1721                          * truncate in progress.
1722                          */
1723                         /*
1724                          * The buffer was zeroed by block_write_full_page()
1725                          */
1726                         clear_buffer_dirty(bh);
1727                         set_buffer_uptodate(bh);
1728                 } else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1729                            buffer_dirty(bh)) {
1730                         WARN_ON(bh->b_size != blocksize);
1731                         err = get_block(inode, block, bh, 1);
1732                         if (err)
1733                                 goto recover;
1734                         clear_buffer_delay(bh);
1735                         if (buffer_new(bh)) {
1736                                 /* blockdev mappings never come here */
1737                                 clear_buffer_new(bh);
1738                                 clean_bdev_bh_alias(bh);
1739                         }
1740                 }
1741                 bh = bh->b_this_page;
1742                 block++;
1743         } while (bh != head);
1744 
1745         do {
1746                 if (!buffer_mapped(bh))
1747                         continue;
1748                 /*
1749                  * If it's a fully non-blocking write attempt and we cannot
1750                  * lock the buffer then redirty the page.  Note that this can
1751                  * potentially cause a busy-wait loop from writeback threads
1752                  * and kswapd activity, but those code paths have their own
1753                  * higher-level throttling.
1754                  */
1755                 if (wbc->sync_mode != WB_SYNC_NONE) {
1756                         lock_buffer(bh);
1757                 } else if (!trylock_buffer(bh)) {
1758                         redirty_page_for_writepage(wbc, page);
1759                         continue;
1760                 }
1761                 if (test_clear_buffer_dirty(bh)) {
1762                         mark_buffer_async_write_endio(bh, handler);
1763                 } else {
1764                         unlock_buffer(bh);
1765                 }
1766         } while ((bh = bh->b_this_page) != head);
1767 
1768         /*
1769          * The page and its buffers are protected by PageWriteback(), so we can
1770          * drop the bh refcounts early.
1771          */
1772         BUG_ON(PageWriteback(page));
1773         set_page_writeback(page);
1774 
1775         do {
1776                 struct buffer_head *next = bh->b_this_page;
1777                 if (buffer_async_write(bh)) {
1778                         submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
1779                                         inode->i_write_hint, wbc);
1780                         nr_underway++;
1781                 }
1782                 bh = next;
1783         } while (bh != head);
1784         unlock_page(page);
1785 
1786         err = 0;
1787 done:
1788         if (nr_underway == 0) {
1789                 /*
1790                  * The page was marked dirty, but the buffers were
1791                  * clean.  Someone wrote them back by hand with
1792                  * ll_rw_block/submit_bh.  A rare case.
1793                  */
1794                 end_page_writeback(page);
1795 
1796                 /*
1797                  * The page and buffer_heads can be released at any time from
1798                  * here on.
1799                  */
1800         }
1801         return err;
1802 
1803 recover:
1804         /*
1805          * ENOSPC, or some other error.  We may already have added some
1806          * blocks to the file, so we need to write these out to avoid
1807          * exposing stale data.
1808          * The page is currently locked and not marked for writeback
1809          */
1810         bh = head;
1811         /* Recovery: lock and submit the mapped buffers */
1812         do {
1813                 if (buffer_mapped(bh) && buffer_dirty(bh) &&
1814                     !buffer_delay(bh)) {
1815                         lock_buffer(bh);
1816                         mark_buffer_async_write_endio(bh, handler);
1817                 } else {
1818                         /*
1819                          * The buffer may have been set dirty during
1820                          * attachment to a dirty page.
1821                          */
1822                         clear_buffer_dirty(bh);
1823                 }
1824         } while ((bh = bh->b_this_page) != head);
1825         SetPageError(page);
1826         BUG_ON(PageWriteback(page));
1827         mapping_set_error(page->mapping, err);
1828         set_page_writeback(page);
1829         do {
1830                 struct buffer_head *next = bh->b_this_page;
1831                 if (buffer_async_write(bh)) {
1832                         clear_buffer_dirty(bh);
1833                         submit_bh_wbc(REQ_OP_WRITE, write_flags, bh,
1834                                         inode->i_write_hint, wbc);
1835                         nr_underway++;
1836                 }
1837                 bh = next;
1838         } while (bh != head);
1839         unlock_page(page);
1840         goto done;
1841 }
1842 EXPORT_SYMBOL(__block_write_full_page);
1843 
1844 /*
1845  * If a page has any new buffers, zero them out here, and mark them uptodate
1846  * and dirty so they'll be written out (in order to prevent uninitialised
1847  * block data from leaking). And clear the new bit.
1848  */
1849 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1850 {
1851         unsigned int block_start, block_end;
1852         struct buffer_head *head, *bh;
1853 
1854         BUG_ON(!PageLocked(page));
1855         if (!page_has_buffers(page))
1856                 return;
1857 
1858         bh = head = page_buffers(page);
1859         block_start = 0;
1860         do {
1861                 block_end = block_start + bh->b_size;
1862 
1863                 if (buffer_new(bh)) {
1864                         if (block_end > from && block_start < to) {
1865                                 if (!PageUptodate(page)) {
1866                                         unsigned start, size;
1867 
1868                                         start = max(from, block_start);
1869                                         size = min(to, block_end) - start;
1870 
1871                                         zero_user(page, start, size);
1872                                         set_buffer_uptodate(bh);
1873                                 }
1874 
1875                                 clear_buffer_new(bh);
1876                                 mark_buffer_dirty(bh);
1877                         }
1878                 }
1879 
1880                 block_start = block_end;
1881                 bh = bh->b_this_page;
1882         } while (bh != head);
1883 }
1884 EXPORT_SYMBOL(page_zero_new_buffers);
1885 
1886 static void
1887 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
1888                 struct iomap *iomap)
1889 {
1890         loff_t offset = block << inode->i_blkbits;
1891 
1892         bh->b_bdev = iomap->bdev;
1893 
1894         /*
1895          * Block points to offset in file we need to map, iomap contains
1896          * the offset at which the map starts. If the map ends before the
1897          * current block, then do not map the buffer and let the caller
1898          * handle it.
1899          */
1900         BUG_ON(offset >= iomap->offset + iomap->length);
1901 
1902         switch (iomap->type) {
1903         case IOMAP_HOLE:
1904                 /*
1905                  * If the buffer is not up to date or beyond the current EOF,
1906                  * we need to mark it as new to ensure sub-block zeroing is
1907                  * executed if necessary.
1908                  */
1909                 if (!buffer_uptodate(bh) ||
1910                     (offset >= i_size_read(inode)))
1911                         set_buffer_new(bh);
1912                 break;
1913         case IOMAP_DELALLOC:
1914                 if (!buffer_uptodate(bh) ||
1915                     (offset >= i_size_read(inode)))
1916                         set_buffer_new(bh);
1917                 set_buffer_uptodate(bh);
1918                 set_buffer_mapped(bh);
1919                 set_buffer_delay(bh);
1920                 break;
1921         case IOMAP_UNWRITTEN:
1922                 /*
1923                  * For unwritten regions, we always need to ensure that regions
1924                  * in the block we are not writing to are zeroed. Mark the
1925                  * buffer as new to ensure this.
1926                  */
1927                 set_buffer_new(bh);
1928                 set_buffer_unwritten(bh);
1929                 /* FALLTHRU */
1930         case IOMAP_MAPPED:
1931                 if ((iomap->flags & IOMAP_F_NEW) ||
1932                     offset >= i_size_read(inode))
1933                         set_buffer_new(bh);
1934                 bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
1935                                 inode->i_blkbits;
1936                 set_buffer_mapped(bh);
1937                 break;
1938         }
1939 }
1940 
1941 int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
1942                 get_block_t *get_block, struct iomap *iomap)
1943 {
1944         unsigned from = pos & (PAGE_SIZE - 1);
1945         unsigned to = from + len;
1946         struct inode *inode = page->mapping->host;
1947         unsigned block_start, block_end;
1948         sector_t block;
1949         int err = 0;
1950         unsigned blocksize, bbits;
1951         struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1952 
1953         BUG_ON(!PageLocked(page));
1954         BUG_ON(from > PAGE_SIZE);
1955         BUG_ON(to > PAGE_SIZE);
1956         BUG_ON(from > to);
1957 
1958         head = create_page_buffers(page, inode, 0);
1959         blocksize = head->b_size;
1960         bbits = block_size_bits(blocksize);
1961 
1962         block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1963 
1964         for(bh = head, block_start = 0; bh != head || !block_start;
1965             block++, block_start=block_end, bh = bh->b_this_page) {
1966                 block_end = block_start + blocksize;
1967                 if (block_end <= from || block_start >= to) {
1968                         if (PageUptodate(page)) {
1969                                 if (!buffer_uptodate(bh))
1970                                         set_buffer_uptodate(bh);
1971                         }
1972                         continue;
1973                 }
1974                 if (buffer_new(bh))
1975                         clear_buffer_new(bh);
1976                 if (!buffer_mapped(bh)) {
1977                         WARN_ON(bh->b_size != blocksize);
1978                         if (get_block) {
1979                                 err = get_block(inode, block, bh, 1);
1980                                 if (err)
1981                                         break;
1982                         } else {
1983                                 iomap_to_bh(inode, block, bh, iomap);
1984                         }
1985 
1986                         if (buffer_new(bh)) {
1987                                 clean_bdev_bh_alias(bh);
1988                                 if (PageUptodate(page)) {
1989                                         clear_buffer_new(bh);
1990                                         set_buffer_uptodate(bh);
1991                                         mark_buffer_dirty(bh);
1992                                         continue;
1993                                 }
1994                                 if (block_end > to || block_start < from)
1995                                         zero_user_segments(page,
1996                                                 to, block_end,
1997                                                 block_start, from);
1998                                 continue;
1999                         }
2000                 }
2001                 if (PageUptodate(page)) {
2002                         if (!buffer_uptodate(bh))
2003                                 set_buffer_uptodate(bh);
2004                         continue; 
2005                 }
2006                 if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
2007                     !buffer_unwritten(bh) &&
2008                      (block_start < from || block_end > to)) {
2009                         ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2010                         *wait_bh++=bh;
2011                 }
2012         }
2013         /*
2014          * If we issued read requests - let them complete.
2015          */
2016         while(wait_bh > wait) {
2017                 wait_on_buffer(*--wait_bh);
2018                 if (!buffer_uptodate(*wait_bh))
2019                         err = -EIO;
2020         }
2021         if (unlikely(err))
2022                 page_zero_new_buffers(page, from, to);
2023         return err;
2024 }
2025 
2026 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
2027                 get_block_t *get_block)
2028 {
2029         return __block_write_begin_int(page, pos, len, get_block, NULL);
2030 }
2031 EXPORT_SYMBOL(__block_write_begin);
2032 
2033 static int __block_commit_write(struct inode *inode, struct page *page,
2034                 unsigned from, unsigned to)
2035 {
2036         unsigned block_start, block_end;
2037         int partial = 0;
2038         unsigned blocksize;
2039         struct buffer_head *bh, *head;
2040 
2041         bh = head = page_buffers(page);
2042         blocksize = bh->b_size;
2043 
2044         block_start = 0;
2045         do {
2046                 block_end = block_start + blocksize;
2047                 if (block_end <= from || block_start >= to) {
2048                         if (!buffer_uptodate(bh))
2049                                 partial = 1;
2050                 } else {
2051                         set_buffer_uptodate(bh);
2052                         mark_buffer_dirty(bh);
2053                 }
2054                 clear_buffer_new(bh);
2055 
2056                 block_start = block_end;
2057                 bh = bh->b_this_page;
2058         } while (bh != head);
2059 
2060         /*
2061          * If this is a partial write which happened to make all buffers
2062          * uptodate then we can optimize away a bogus readpage() for
2063          * the next read(). Here we 'discover' whether the page went
2064          * uptodate as a result of this (potentially partial) write.
2065          */
2066         if (!partial)
2067                 SetPageUptodate(page);
2068         return 0;
2069 }
2070 
2071 /*
2072  * block_write_begin takes care of the basic task of block allocation and
2073  * bringing partial write blocks uptodate first.
2074  *
2075  * The filesystem needs to handle block truncation upon failure.
2076  */
2077 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2078                 unsigned flags, struct page **pagep, get_block_t *get_block)
2079 {
2080         pgoff_t index = pos >> PAGE_SHIFT;
2081         struct page *page;
2082         int status;
2083 
2084         page = grab_cache_page_write_begin(mapping, index, flags);
2085         if (!page)
2086                 return -ENOMEM;
2087 
2088         status = __block_write_begin(page, pos, len, get_block);
2089         if (unlikely(status)) {
2090                 unlock_page(page);
2091                 put_page(page);
2092                 page = NULL;
2093         }
2094 
2095         *pagep = page;
2096         return status;
2097 }
2098 EXPORT_SYMBOL(block_write_begin);
2099 
2100 int block_write_end(struct file *file, struct address_space *mapping,
2101                         loff_t pos, unsigned len, unsigned copied,
2102                         struct page *page, void *fsdata)
2103 {
2104         struct inode *inode = mapping->host;
2105         unsigned start;
2106 
2107         start = pos & (PAGE_SIZE - 1);
2108 
2109         if (unlikely(copied < len)) {
2110                 /*
2111                  * The buffers that were written will now be uptodate, so we
2112                  * don't have to worry about a readpage reading them and
2113                  * overwriting a partial write. However if we have encountered
2114                  * a short write and only partially written into a buffer, it
2115                  * will not be marked uptodate, so a readpage might come in and
2116                  * destroy our partial write.
2117                  *
2118                  * Do the simplest thing, and just treat any short write to a
2119                  * non uptodate page as a zero-length write, and force the
2120                  * caller to redo the whole thing.
2121                  */
2122                 if (!PageUptodate(page))
2123                         copied = 0;
2124 
2125                 page_zero_new_buffers(page, start+copied, start+len);
2126         }
2127         flush_dcache_page(page);
2128 
2129         /* This could be a short (even 0-length) commit */
2130         __block_commit_write(inode, page, start, start+copied);
2131 
2132         return copied;
2133 }
2134 EXPORT_SYMBOL(block_write_end);
2135 
2136 int generic_write_end(struct file *file, struct address_space *mapping,
2137                         loff_t pos, unsigned len, unsigned copied,
2138                         struct page *page, void *fsdata)
2139 {
2140         struct inode *inode = mapping->host;
2141         loff_t old_size = inode->i_size;
2142         bool i_size_changed = false;
2143 
2144         copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2145 
2146         /*
2147          * No need to use i_size_read() here, the i_size cannot change under us
2148          * because we hold i_rwsem.
2149          *
2150          * But it's important to update i_size while still holding page lock:
2151          * page writeout could otherwise come in and zero beyond i_size.
2152          */
2153         if (pos + copied > inode->i_size) {
2154                 i_size_write(inode, pos + copied);
2155                 i_size_changed = true;
2156         }
2157 
2158         unlock_page(page);
2159         put_page(page);
2160 
2161         if (old_size < pos)
2162                 pagecache_isize_extended(inode, old_size, pos);
2163         /*
2164          * Don't mark the inode dirty under page lock. First, it unnecessarily
2165          * makes the holding time of page lock longer. Second, it forces lock
2166          * ordering of page lock and transaction start for journaling
2167          * filesystems.
2168          */
2169         if (i_size_changed)
2170                 mark_inode_dirty(inode);
2171         return copied;
2172 }
2173 EXPORT_SYMBOL(generic_write_end);
2174 
2175 /*
2176  * block_is_partially_uptodate checks whether buffers within a page are
2177  * uptodate or not.
2178  *
2179  * Returns true if all buffers which correspond to a file portion
2180  * we want to read are uptodate.
2181  */
2182 int block_is_partially_uptodate(struct page *page, unsigned long from,
2183                                         unsigned long count)
2184 {
2185         unsigned block_start, block_end, blocksize;
2186         unsigned to;
2187         struct buffer_head *bh, *head;
2188         int ret = 1;
2189 
2190         if (!page_has_buffers(page))
2191                 return 0;
2192 
2193         head = page_buffers(page);
2194         blocksize = head->b_size;
2195         to = min_t(unsigned, PAGE_SIZE - from, count);
2196         to = from + to;
2197         if (from < blocksize && to > PAGE_SIZE - blocksize)
2198                 return 0;
2199 
2200         bh = head;
2201         block_start = 0;
2202         do {
2203                 block_end = block_start + blocksize;
2204                 if (block_end > from && block_start < to) {
2205                         if (!buffer_uptodate(bh)) {
2206                                 ret = 0;
2207                                 break;
2208                         }
2209                         if (block_end >= to)
2210                                 break;
2211                 }
2212                 block_start = block_end;
2213                 bh = bh->b_this_page;
2214         } while (bh != head);
2215 
2216         return ret;
2217 }
2218 EXPORT_SYMBOL(block_is_partially_uptodate);
2219 
2220 /*
2221  * Generic "read page" function for block devices that have the normal
2222  * get_block functionality. This is most of the block device filesystems.
2223  * Reads the page asynchronously --- the unlock_buffer() and
2224  * set/clear_buffer_uptodate() functions propagate buffer state into the
2225  * page struct once IO has completed.
2226  */
2227 int block_read_full_page(struct page *page, get_block_t *get_block)
2228 {
2229         struct inode *inode = page->mapping->host;
2230         sector_t iblock, lblock;
2231         struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2232         unsigned int blocksize, bbits;
2233         int nr, i;
2234         int fully_mapped = 1;
2235 
2236         head = create_page_buffers(page, inode, 0);
2237         blocksize = head->b_size;
2238         bbits = block_size_bits(blocksize);
2239 
2240         iblock = (sector_t)page->index << (PAGE_SHIFT - bbits);
2241         lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2242         bh = head;
2243         nr = 0;
2244         i = 0;
2245 
2246         do {
2247                 if (buffer_uptodate(bh))
2248                         continue;
2249 
2250                 if (!buffer_mapped(bh)) {
2251                         int err = 0;
2252 
2253                         fully_mapped = 0;
2254                         if (iblock < lblock) {
2255                                 WARN_ON(bh->b_size != blocksize);
2256                                 err = get_block(inode, iblock, bh, 0);
2257                                 if (err)
2258                                         SetPageError(page);
2259                         }
2260                         if (!buffer_mapped(bh)) {
2261                                 zero_user(page, i * blocksize, blocksize);
2262                                 if (!err)
2263                                         set_buffer_uptodate(bh);
2264                                 continue;
2265                         }
2266                         /*
2267                          * get_block() might have updated the buffer
2268                          * synchronously
2269                          */
2270                         if (buffer_uptodate(bh))
2271                                 continue;
2272                 }
2273                 arr[nr++] = bh;
2274         } while (i++, iblock++, (bh = bh->b_this_page) != head);
2275 
2276         if (fully_mapped)
2277                 SetPageMappedToDisk(page);
2278 
2279         if (!nr) {
2280                 /*
2281                  * All buffers are uptodate - we can set the page uptodate
2282                  * as well. But not if get_block() returned an error.
2283                  */
2284                 if (!PageError(page))
2285                         SetPageUptodate(page);
2286                 unlock_page(page);
2287                 return 0;
2288         }
2289 
2290         /* Stage two: lock the buffers */
2291         for (i = 0; i < nr; i++) {
2292                 bh = arr[i];
2293                 lock_buffer(bh);
2294                 mark_buffer_async_read(bh);
2295         }
2296 
2297         /*
2298          * Stage 3: start the IO.  Check for uptodateness
2299          * inside the buffer lock in case another process reading
2300          * the underlying blockdev brought it uptodate (the sct fix).
2301          */
2302         for (i = 0; i < nr; i++) {
2303                 bh = arr[i];
2304                 if (buffer_uptodate(bh))
2305                         end_buffer_async_read(bh, 1);
2306                 else
2307                         submit_bh(REQ_OP_READ, 0, bh);
2308         }
2309         return 0;
2310 }
2311 EXPORT_SYMBOL(block_read_full_page);
2312 
2313 /* utility function for filesystems that need to do work on expanding
2314  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2315  * deal with the hole.  
2316  */
2317 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2318 {
2319         struct address_space *mapping = inode->i_mapping;
2320         struct page *page;
2321         void *fsdata;
2322         int err;
2323 
2324         err = inode_newsize_ok(inode, size);
2325         if (err)
2326                 goto out;
2327 
2328         err = pagecache_write_begin(NULL, mapping, size, 0,
2329                                     AOP_FLAG_CONT_EXPAND, &page, &fsdata);
2330         if (err)
2331                 goto out;
2332 
2333         err = pagecache_write_end(NULL, mapping, size, 0, 0, page, fsdata);
2334         BUG_ON(err > 0);
2335 
2336 out:
2337         return err;
2338 }
2339 EXPORT_SYMBOL(generic_cont_expand_simple);
2340 
2341 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2342                             loff_t pos, loff_t *bytes)
2343 {
2344         struct inode *inode = mapping->host;
2345         unsigned int blocksize = i_blocksize(inode);
2346         struct page *page;
2347         void *fsdata;
2348         pgoff_t index, curidx;
2349         loff_t curpos;
2350         unsigned zerofrom, offset, len;
2351         int err = 0;
2352 
2353         index = pos >> PAGE_SHIFT;
2354         offset = pos & ~PAGE_MASK;
2355 
2356         while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2357                 zerofrom = curpos & ~PAGE_MASK;
2358                 if (zerofrom & (blocksize-1)) {
2359                         *bytes |= (blocksize-1);
2360                         (*bytes)++;
2361                 }
2362                 len = PAGE_SIZE - zerofrom;
2363 
2364                 err = pagecache_write_begin(file, mapping, curpos, len, 0,
2365                                             &page, &fsdata);
2366                 if (err)
2367                         goto out;
2368                 zero_user(page, zerofrom, len);
2369                 err = pagecache_write_end(file, mapping, curpos, len, len,
2370                                                 page, fsdata);
2371                 if (err < 0)
2372                         goto out;
2373                 BUG_ON(err != len);
2374                 err = 0;
2375 
2376                 balance_dirty_pages_ratelimited(mapping);
2377 
2378                 if (fatal_signal_pending(current)) {
2379                         err = -EINTR;
2380                         goto out;
2381                 }
2382         }
2383 
2384         /* page covers the boundary, find the boundary offset */
2385         if (index == curidx) {
2386                 zerofrom = curpos & ~PAGE_MASK;
2387                 /* if we will expand the thing last block will be filled */
2388                 if (offset <= zerofrom) {
2389                         goto out;
2390                 }
2391                 if (zerofrom & (blocksize-1)) {
2392                         *bytes |= (blocksize-1);
2393                         (*bytes)++;
2394                 }
2395                 len = offset - zerofrom;
2396 
2397                 err = pagecache_write_begin(file, mapping, curpos, len, 0,
2398                                             &page, &fsdata);
2399                 if (err)
2400                         goto out;
2401                 zero_user(page, zerofrom, len);
2402                 err = pagecache_write_end(file, mapping, curpos, len, len,
2403                                                 page, fsdata);
2404                 if (err < 0)
2405                         goto out;
2406                 BUG_ON(err != len);
2407                 err = 0;
2408         }
2409 out:
2410         return err;
2411 }
2412 
2413 /*
2414  * For moronic filesystems that do not allow holes in file.
2415  * We may have to extend the file.
2416  */
2417 int cont_write_begin(struct file *file, struct address_space *mapping,
2418                         loff_t pos, unsigned len, unsigned flags,
2419                         struct page **pagep, void **fsdata,
2420                         get_block_t *get_block, loff_t *bytes)
2421 {
2422         struct inode *inode = mapping->host;
2423         unsigned int blocksize = i_blocksize(inode);
2424         unsigned int zerofrom;
2425         int err;
2426 
2427         err = cont_expand_zero(file, mapping, pos, bytes);
2428         if (err)
2429                 return err;
2430 
2431         zerofrom = *bytes & ~PAGE_MASK;
2432         if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2433                 *bytes |= (blocksize-1);
2434                 (*bytes)++;
2435         }
2436 
2437         return block_write_begin(mapping, pos, len, flags, pagep, get_block);
2438 }
2439 EXPORT_SYMBOL(cont_write_begin);
2440 
2441 int block_commit_write(struct page *page, unsigned from, unsigned to)
2442 {
2443         struct inode *inode = page->mapping->host;
2444         __block_commit_write(inode,page,from,to);
2445         return 0;
2446 }
2447 EXPORT_SYMBOL(block_commit_write);
2448 
2449 /*
2450  * block_page_mkwrite() is not allowed to change the file size as it gets
2451  * called from a page fault handler when a page is first dirtied. Hence we must
2452  * be careful to check for EOF conditions here. We set the page up correctly
2453  * for a written page which means we get ENOSPC checking when writing into
2454  * holes and correct delalloc and unwritten extent mapping on filesystems that
2455  * support these features.
2456  *
2457  * We are not allowed to take the i_mutex here so we have to play games to
2458  * protect against truncate races as the page could now be beyond EOF.  Because
2459  * truncate writes the inode size before removing pages, once we have the
2460  * page lock we can determine safely if the page is beyond EOF. If it is not
2461  * beyond EOF, then the page is guaranteed safe against truncation until we
2462  * unlock the page.
2463  *
2464  * Direct callers of this function should protect against filesystem freezing
2465  * using sb_start_pagefault() - sb_end_pagefault() functions.
2466  */
2467 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2468                          get_block_t get_block)
2469 {
2470         struct page *page = vmf->page;
2471         struct inode *inode = file_inode(vma->vm_file);
2472         unsigned long end;
2473         loff_t size;
2474         int ret;
2475 
2476         lock_page(page);
2477         size = i_size_read(inode);
2478         if ((page->mapping != inode->i_mapping) ||
2479             (page_offset(page) > size)) {
2480                 /* We overload EFAULT to mean page got truncated */
2481                 ret = -EFAULT;
2482                 goto out_unlock;
2483         }
2484 
2485         /* page is wholly or partially inside EOF */
2486         if (((page->index + 1) << PAGE_SHIFT) > size)
2487                 end = size & ~PAGE_MASK;
2488         else
2489                 end = PAGE_SIZE;
2490 
2491         ret = __block_write_begin(page, 0, end, get_block);
2492         if (!ret)
2493                 ret = block_commit_write(page, 0, end);
2494 
2495         if (unlikely(ret < 0))
2496                 goto out_unlock;
2497         set_page_dirty(page);
2498         wait_for_stable_page(page);
2499         return 0;
2500 out_unlock:
2501         unlock_page(page);
2502         return ret;
2503 }
2504 EXPORT_SYMBOL(block_page_mkwrite);
2505 
2506 /*
2507  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2508  * immediately, while under the page lock.  So it needs a special end_io
2509  * handler which does not touch the bh after unlocking it.
2510  */
2511 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2512 {
2513         __end_buffer_read_notouch(bh, uptodate);
2514 }
2515 
2516 /*
2517  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2518  * the page (converting it to circular linked list and taking care of page
2519  * dirty races).
2520  */
2521 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2522 {
2523         struct buffer_head *bh;
2524 
2525         BUG_ON(!PageLocked(page));
2526 
2527         spin_lock(&page->mapping->private_lock);
2528         bh = head;
2529         do {
2530                 if (PageDirty(page))
2531                         set_buffer_dirty(bh);
2532                 if (!bh->b_this_page)
2533                         bh->b_this_page = head;
2534                 bh = bh->b_this_page;
2535         } while (bh != head);
2536         attach_page_buffers(page, head);
2537         spin_unlock(&page->mapping->private_lock);
2538 }
2539 
2540 /*
2541  * On entry, the page is fully not uptodate.
2542  * On exit the page is fully uptodate in the areas outside (from,to)
2543  * The filesystem needs to handle block truncation upon failure.
2544  */
2545 int nobh_write_begin(struct address_space *mapping,
2546                         loff_t pos, unsigned len, unsigned flags,
2547                         struct page **pagep, void **fsdata,
2548                         get_block_t *get_block)
2549 {
2550         struct inode *inode = mapping->host;
2551         const unsigned blkbits = inode->i_blkbits;
2552         const unsigned blocksize = 1 << blkbits;
2553         struct buffer_head *head, *bh;
2554         struct page *page;
2555         pgoff_t index;
2556         unsigned from, to;
2557         unsigned block_in_page;
2558         unsigned block_start, block_end;
2559         sector_t block_in_file;
2560         int nr_reads = 0;
2561         int ret = 0;
2562         int is_mapped_to_disk = 1;
2563 
2564         index = pos >> PAGE_SHIFT;
2565         from = pos & (PAGE_SIZE - 1);
2566         to = from + len;
2567 
2568         page = grab_cache_page_write_begin(mapping, index, flags);
2569         if (!page)
2570                 return -ENOMEM;
2571         *pagep = page;
2572         *fsdata = NULL;
2573 
2574         if (page_has_buffers(page)) {
2575                 ret = __block_write_begin(page, pos, len, get_block);
2576                 if (unlikely(ret))
2577                         goto out_release;
2578                 return ret;
2579         }
2580 
2581         if (PageMappedToDisk(page))
2582                 return 0;
2583 
2584         /*
2585          * Allocate buffers so that we can keep track of state, and potentially
2586          * attach them to the page if an error occurs. In the common case of
2587          * no error, they will just be freed again without ever being attached
2588          * to the page (which is all OK, because we're under the page lock).
2589          *
2590          * Be careful: the buffer linked list is a NULL terminated one, rather
2591          * than the circular one we're used to.
2592          */
2593         head = alloc_page_buffers(page, blocksize, false);
2594         if (!head) {
2595                 ret = -ENOMEM;
2596                 goto out_release;
2597         }
2598 
2599         block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2600 
2601         /*
2602          * We loop across all blocks in the page, whether or not they are
2603          * part of the affected region.  This is so we can discover if the
2604          * page is fully mapped-to-disk.
2605          */
2606         for (block_start = 0, block_in_page = 0, bh = head;
2607                   block_start < PAGE_SIZE;
2608                   block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2609                 int create;
2610 
2611                 block_end = block_start + blocksize;
2612                 bh->b_state = 0;
2613                 create = 1;
2614                 if (block_start >= to)
2615                         create = 0;
2616                 ret = get_block(inode, block_in_file + block_in_page,
2617                                         bh, create);
2618                 if (ret)
2619                         goto failed;
2620                 if (!buffer_mapped(bh))
2621                         is_mapped_to_disk = 0;
2622                 if (buffer_new(bh))
2623                         clean_bdev_bh_alias(bh);
2624                 if (PageUptodate(page)) {
2625                         set_buffer_uptodate(bh);
2626                         continue;
2627                 }
2628                 if (buffer_new(bh) || !buffer_mapped(bh)) {
2629                         zero_user_segments(page, block_start, from,
2630                                                         to, block_end);
2631                         continue;
2632                 }
2633                 if (buffer_uptodate(bh))
2634                         continue;       /* reiserfs does this */
2635                 if (block_start < from || block_end > to) {
2636                         lock_buffer(bh);
2637                         bh->b_end_io = end_buffer_read_nobh;
2638                         submit_bh(REQ_OP_READ, 0, bh);
2639                         nr_reads++;
2640                 }
2641         }
2642 
2643         if (nr_reads) {
2644                 /*
2645                  * The page is locked, so these buffers are protected from
2646                  * any VM or truncate activity.  Hence we don't need to care
2647                  * for the buffer_head refcounts.
2648                  */
2649                 for (bh = head; bh; bh = bh->b_this_page) {
2650                         wait_on_buffer(bh);
2651                         if (!buffer_uptodate(bh))
2652                                 ret = -EIO;
2653                 }
2654                 if (ret)
2655                         goto failed;
2656         }
2657 
2658         if (is_mapped_to_disk)
2659                 SetPageMappedToDisk(page);
2660 
2661         *fsdata = head; /* to be released by nobh_write_end */
2662 
2663         return 0;
2664 
2665 failed:
2666         BUG_ON(!ret);
2667         /*
2668          * Error recovery is a bit difficult. We need to zero out blocks that
2669          * were newly allocated, and dirty them to ensure they get written out.
2670          * Buffers need to be attached to the page at this point, otherwise
2671          * the handling of potential IO errors during writeout would be hard
2672          * (could try doing synchronous writeout, but what if that fails too?)
2673          */
2674         attach_nobh_buffers(page, head);
2675         page_zero_new_buffers(page, from, to);
2676 
2677 out_release:
2678         unlock_page(page);
2679         put_page(page);
2680         *pagep = NULL;
2681 
2682         return ret;
2683 }
2684 EXPORT_SYMBOL(nobh_write_begin);
2685 
2686 int nobh_write_end(struct file *file, struct address_space *mapping,
2687                         loff_t pos, unsigned len, unsigned copied,
2688                         struct page *page, void *fsdata)
2689 {
2690         struct inode *inode = page->mapping->host;
2691         struct buffer_head *head = fsdata;
2692         struct buffer_head *bh;
2693         BUG_ON(fsdata != NULL && page_has_buffers(page));
2694 
2695         if (unlikely(copied < len) && head)
2696                 attach_nobh_buffers(page, head);
2697         if (page_has_buffers(page))
2698                 return generic_write_end(file, mapping, pos, len,
2699                                         copied, page, fsdata);
2700 
2701         SetPageUptodate(page);
2702         set_page_dirty(page);
2703         if (pos+copied > inode->i_size) {
2704                 i_size_write(inode, pos+copied);
2705                 mark_inode_dirty(inode);
2706         }
2707 
2708         unlock_page(page);
2709         put_page(page);
2710 
2711         while (head) {
2712                 bh = head;
2713                 head = head->b_this_page;
2714                 free_buffer_head(bh);
2715         }
2716 
2717         return copied;
2718 }
2719 EXPORT_SYMBOL(nobh_write_end);
2720 
2721 /*
2722  * nobh_writepage() - based on block_full_write_page() except
2723  * that it tries to operate without attaching bufferheads to
2724  * the page.
2725  */
2726 int nobh_writepage(struct page *page, get_block_t *get_block,
2727                         struct writeback_control *wbc)
2728 {
2729         struct inode * const inode = page->mapping->host;
2730         loff_t i_size = i_size_read(inode);
2731         const pgoff_t end_index = i_size >> PAGE_SHIFT;
2732         unsigned offset;
2733         int ret;
2734 
2735         /* Is the page fully inside i_size? */
2736         if (page->index < end_index)
2737                 goto out;
2738 
2739         /* Is the page fully outside i_size? (truncate in progress) */
2740         offset = i_size & (PAGE_SIZE-1);
2741         if (page->index >= end_index+1 || !offset) {
2742                 /*
2743                  * The page may have dirty, unmapped buffers.  For example,
2744                  * they may have been added in ext3_writepage().  Make them
2745                  * freeable here, so the page does not leak.
2746                  */
2747 #if 0
2748                 /* Not really sure about this  - do we need this ? */
2749                 if (page->mapping->a_ops->invalidatepage)
2750                         page->mapping->a_ops->invalidatepage(page, offset);
2751 #endif
2752                 unlock_page(page);
2753                 return 0; /* don't care */
2754         }
2755 
2756         /*
2757          * The page straddles i_size.  It must be zeroed out on each and every
2758          * writepage invocation because it may be mmapped.  "A file is mapped
2759          * in multiples of the page size.  For a file that is not a multiple of
2760          * the  page size, the remaining memory is zeroed when mapped, and
2761          * writes to that region are not written out to the file."
2762          */
2763         zero_user_segment(page, offset, PAGE_SIZE);
2764 out:
2765         ret = mpage_writepage(page, get_block, wbc);
2766         if (ret == -EAGAIN)
2767                 ret = __block_write_full_page(inode, page, get_block, wbc,
2768                                               end_buffer_async_write);
2769         return ret;
2770 }
2771 EXPORT_SYMBOL(nobh_writepage);
2772 
2773 int nobh_truncate_page(struct address_space *mapping,
2774                         loff_t from, get_block_t *get_block)
2775 {
2776         pgoff_t index = from >> PAGE_SHIFT;
2777         unsigned offset = from & (PAGE_SIZE-1);
2778         unsigned blocksize;
2779         sector_t iblock;
2780         unsigned length, pos;
2781         struct inode *inode = mapping->host;
2782         struct page *page;
2783         struct buffer_head map_bh;
2784         int err;
2785 
2786         blocksize = i_blocksize(inode);
2787         length = offset & (blocksize - 1);
2788 
2789         /* Block boundary? Nothing to do */
2790         if (!length)
2791                 return 0;
2792 
2793         length = blocksize - length;
2794         iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2795 
2796         page = grab_cache_page(mapping, index);
2797         err = -ENOMEM;
2798         if (!page)
2799                 goto out;
2800 
2801         if (page_has_buffers(page)) {
2802 has_buffers:
2803                 unlock_page(page);
2804                 put_page(page);
2805                 return block_truncate_page(mapping, from, get_block);
2806         }
2807 
2808         /* Find the buffer that contains "offset" */
2809         pos = blocksize;
2810         while (offset >= pos) {
2811                 iblock++;
2812                 pos += blocksize;
2813         }
2814 
2815         map_bh.b_size = blocksize;
2816         map_bh.b_state = 0;
2817         err = get_block(inode, iblock, &map_bh, 0);
2818         if (err)
2819                 goto unlock;
2820         /* unmapped? It's a hole - nothing to do */
2821         if (!buffer_mapped(&map_bh))
2822                 goto unlock;
2823 
2824         /* Ok, it's mapped. Make sure it's up-to-date */
2825         if (!PageUptodate(page)) {
2826                 err = mapping->a_ops->readpage(NULL, page);
2827                 if (err) {
2828                         put_page(page);
2829                         goto out;
2830                 }
2831                 lock_page(page);
2832                 if (!PageUptodate(page)) {
2833                         err = -EIO;
2834                         goto unlock;
2835                 }
2836                 if (page_has_buffers(page))
2837                         goto has_buffers;
2838         }
2839         zero_user(page, offset, length);
2840         set_page_dirty(page);
2841         err = 0;
2842 
2843 unlock:
2844         unlock_page(page);
2845         put_page(page);
2846 out:
2847         return err;
2848 }
2849 EXPORT_SYMBOL(nobh_truncate_page);
2850 
2851 int block_truncate_page(struct address_space *mapping,
2852                         loff_t from, get_block_t *get_block)
2853 {
2854         pgoff_t index = from >> PAGE_SHIFT;
2855         unsigned offset = from & (PAGE_SIZE-1);
2856         unsigned blocksize;
2857         sector_t iblock;
2858         unsigned length, pos;
2859         struct inode *inode = mapping->host;
2860         struct page *page;
2861         struct buffer_head *bh;
2862         int err;
2863 
2864         blocksize = i_blocksize(inode);
2865         length = offset & (blocksize - 1);
2866 
2867         /* Block boundary? Nothing to do */
2868         if (!length)
2869                 return 0;
2870 
2871         length = blocksize - length;
2872         iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2873         
2874         page = grab_cache_page(mapping, index);
2875         err = -ENOMEM;
2876         if (!page)
2877                 goto out;
2878 
2879         if (!page_has_buffers(page))
2880                 create_empty_buffers(page, blocksize, 0);
2881 
2882         /* Find the buffer that contains "offset" */
2883         bh = page_buffers(page);
2884         pos = blocksize;
2885         while (offset >= pos) {
2886                 bh = bh->b_this_page;
2887                 iblock++;
2888                 pos += blocksize;
2889         }
2890 
2891         err = 0;
2892         if (!buffer_mapped(bh)) {
2893                 WARN_ON(bh->b_size != blocksize);
2894                 err = get_block(inode, iblock, bh, 0);
2895                 if (err)
2896                         goto unlock;
2897                 /* unmapped? It's a hole - nothing to do */
2898                 if (!buffer_mapped(bh))
2899                         goto unlock;
2900         }
2901 
2902         /* Ok, it's mapped. Make sure it's up-to-date */
2903         if (PageUptodate(page))
2904                 set_buffer_uptodate(bh);
2905 
2906         if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2907                 err = -EIO;
2908                 ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2909                 wait_on_buffer(bh);
2910                 /* Uhhuh. Read error. Complain and punt. */
2911                 if (!buffer_uptodate(bh))
2912                         goto unlock;
2913         }
2914 
2915         zero_user(page, offset, length);
2916         mark_buffer_dirty(bh);
2917         err = 0;
2918 
2919 unlock:
2920         unlock_page(page);
2921         put_page(page);
2922 out:
2923         return err;
2924 }
2925 EXPORT_SYMBOL(block_truncate_page);
2926 
2927 /*
2928  * The generic ->writepage function for buffer-backed address_spaces
2929  */
2930 int block_write_full_page(struct page *page, get_block_t *get_block,
2931                         struct writeback_control *wbc)
2932 {
2933         struct inode * const inode = page->mapping->host;
2934         loff_t i_size = i_size_read(inode);
2935         const pgoff_t end_index = i_size >> PAGE_SHIFT;
2936         unsigned offset;
2937 
2938         /* Is the page fully inside i_size? */
2939         if (page->index < end_index)
2940                 return __block_write_full_page(inode, page, get_block, wbc,
2941                                                end_buffer_async_write);
2942 
2943         /* Is the page fully outside i_size? (truncate in progress) */
2944         offset = i_size & (PAGE_SIZE-1);
2945         if (page->index >= end_index+1 || !offset) {
2946                 /*
2947                  * The page may have dirty, unmapped buffers.  For example,
2948                  * they may have been added in ext3_writepage().  Make them
2949                  * freeable here, so the page does not leak.
2950                  */
2951                 do_invalidatepage(page, 0, PAGE_SIZE);
2952                 unlock_page(page);
2953                 return 0; /* don't care */
2954         }
2955 
2956         /*
2957          * The page straddles i_size.  It must be zeroed out on each and every
2958          * writepage invocation because it may be mmapped.  "A file is mapped
2959          * in multiples of the page size.  For a file that is not a multiple of
2960          * the  page size, the remaining memory is zeroed when mapped, and
2961          * writes to that region are not written out to the file."
2962          */
2963         zero_user_segment(page, offset, PAGE_SIZE);
2964         return __block_write_full_page(inode, page, get_block, wbc,
2965                                                         end_buffer_async_write);
2966 }
2967 EXPORT_SYMBOL(block_write_full_page);
2968 
2969 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2970                             get_block_t *get_block)
2971 {
2972         struct inode *inode = mapping->host;
2973         struct buffer_head tmp = {
2974                 .b_size = i_blocksize(inode),
2975         };
2976 
2977         get_block(inode, block, &tmp, 0);
2978         return tmp.b_blocknr;
2979 }
2980 EXPORT_SYMBOL(generic_block_bmap);
2981 
2982 static void end_bio_bh_io_sync(struct bio *bio)
2983 {
2984         struct buffer_head *bh = bio->bi_private;
2985 
2986         if (unlikely(bio_flagged(bio, BIO_QUIET)))
2987                 set_bit(BH_Quiet, &bh->b_state);
2988 
2989         bh->b_end_io(bh, !bio->bi_status);
2990         bio_put(bio);
2991 }
2992 
2993 /*
2994  * This allows us to do IO even on the odd last sectors
2995  * of a device, even if the block size is some multiple
2996  * of the physical sector size.
2997  *
2998  * We'll just truncate the bio to the size of the device,
2999  * and clear the end of the buffer head manually.
3000  *
3001  * Truly out-of-range accesses will turn into actual IO
3002  * errors, this only handles the "we need to be able to
3003  * do IO at the final sector" case.
3004  */
3005 void guard_bio_eod(struct bio *bio)
3006 {
3007         sector_t maxsector;
3008         struct hd_struct *part;
3009 
3010         rcu_read_lock();
3011         part = __disk_get_part(bio->bi_disk, bio->bi_partno);
3012         if (part)
3013                 maxsector = part_nr_sects_read(part);
3014         else
3015                 maxsector = get_capacity(bio->bi_disk);
3016         rcu_read_unlock();
3017 
3018         if (!maxsector)
3019                 return;
3020 
3021         /*
3022          * If the *whole* IO is past the end of the device,
3023          * let it through, and the IO layer will turn it into
3024          * an EIO.
3025          */
3026         if (unlikely(bio->bi_iter.bi_sector >= maxsector))
3027                 return;
3028 
3029         maxsector -= bio->bi_iter.bi_sector;
3030         if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
3031                 return;
3032 
3033         bio_truncate(bio, maxsector << 9);
3034 }
3035 
3036 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
3037                          enum rw_hint write_hint, struct writeback_control *wbc)
3038 {
3039         struct bio *bio;
3040 
3041         BUG_ON(!buffer_locked(bh));
3042         BUG_ON(!buffer_mapped(bh));
3043         BUG_ON(!bh->b_end_io);
3044         BUG_ON(buffer_delay(bh));
3045         BUG_ON(buffer_unwritten(bh));
3046 
3047         /*
3048          * Only clear out a write error when rewriting
3049          */
3050         if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
3051                 clear_buffer_write_io_error(bh);
3052 
3053         /*
3054          * from here on down, it's all bio -- do the initial mapping,
3055          * submit_bio -> generic_make_request may further map this bio around
3056          */
3057         bio = bio_alloc(GFP_NOIO, 1);
3058 
3059         bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3060         bio_set_dev(bio, bh->b_bdev);
3061         bio->bi_write_hint = write_hint;
3062 
3063         bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3064         BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3065 
3066         bio->bi_end_io = end_bio_bh_io_sync;
3067         bio->bi_private = bh;
3068 
3069         if (buffer_meta(bh))
3070                 op_flags |= REQ_META;
3071         if (buffer_prio(bh))
3072                 op_flags |= REQ_PRIO;
3073         bio_set_op_attrs(bio, op, op_flags);
3074 
3075         /* Take care of bh's that straddle the end of the device */
3076         guard_bio_eod(bio);
3077 
3078         if (wbc) {
3079                 wbc_init_bio(wbc, bio);
3080                 wbc_account_cgroup_owner(wbc, bh->b_page, bh->b_size);
3081         }
3082 
3083         submit_bio(bio);
3084         return 0;
3085 }
3086 
3087 int submit_bh(int op, int op_flags, struct buffer_head *bh)
3088 {
3089         return submit_bh_wbc(op, op_flags, bh, 0, NULL);
3090 }
3091 EXPORT_SYMBOL(submit_bh);
3092 
3093 /**
3094  * ll_rw_block: low-level access to block devices (DEPRECATED)
3095  * @op: whether to %READ or %WRITE
3096  * @op_flags: req_flag_bits
3097  * @nr: number of &struct buffer_heads in the array
3098  * @bhs: array of pointers to &struct buffer_head
3099  *
3100  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3101  * requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
3102  * @op_flags contains flags modifying the detailed I/O behavior, most notably
3103  * %REQ_RAHEAD.
3104  *
3105  * This function drops any buffer that it cannot get a lock on (with the
3106  * BH_Lock state bit), any buffer that appears to be clean when doing a write
3107  * request, and any buffer that appears to be up-to-date when doing read
3108  * request.  Further it marks as clean buffers that are processed for
3109  * writing (the buffer cache won't assume that they are actually clean
3110  * until the buffer gets unlocked).
3111  *
3112  * ll_rw_block sets b_end_io to simple completion handler that marks
3113  * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3114  * any waiters. 
3115  *
3116  * All of the buffers must be for the same device, and must also be a
3117  * multiple of the current approved size for the device.
3118  */
3119 void ll_rw_block(int op, int op_flags,  int nr, struct buffer_head *bhs[])
3120 {
3121         int i;
3122 
3123         for (i = 0; i < nr; i++) {
3124                 struct buffer_head *bh = bhs[i];
3125 
3126                 if (!trylock_buffer(bh))
3127                         continue;
3128                 if (op == WRITE) {
3129                         if (test_clear_buffer_dirty(bh)) {
3130                                 bh->b_end_io = end_buffer_write_sync;
3131                                 get_bh(bh);
3132                                 submit_bh(op, op_flags, bh);
3133                                 continue;
3134                         }
3135                 } else {
3136                         if (!buffer_uptodate(bh)) {
3137                                 bh->b_end_io = end_buffer_read_sync;
3138                                 get_bh(bh);
3139                                 submit_bh(op, op_flags, bh);
3140                                 continue;
3141                         }
3142                 }
3143                 unlock_buffer(bh);
3144         }
3145 }
3146 EXPORT_SYMBOL(ll_rw_block);
3147 
3148 void write_dirty_buffer(struct buffer_head *bh, int op_flags)
3149 {
3150         lock_buffer(bh);
3151         if (!test_clear_buffer_dirty(bh)) {
3152                 unlock_buffer(bh);
3153                 return;
3154         }
3155         bh->b_end_io = end_buffer_write_sync;
3156         get_bh(bh);
3157         submit_bh(REQ_OP_WRITE, op_flags, bh);
3158 }
3159 EXPORT_SYMBOL(write_dirty_buffer);
3160 
3161 /*
3162  * For a data-integrity writeout, we need to wait upon any in-progress I/O
3163  * and then start new I/O and then wait upon it.  The caller must have a ref on
3164  * the buffer_head.
3165  */
3166 int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
3167 {
3168         int ret = 0;
3169 
3170         WARN_ON(atomic_read(&bh->b_count) < 1);
3171         lock_buffer(bh);
3172         if (test_clear_buffer_dirty(bh)) {
3173                 get_bh(bh);
3174                 bh->b_end_io = end_buffer_write_sync;
3175                 ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
3176                 wait_on_buffer(bh);
3177                 if (!ret && !buffer_uptodate(bh))
3178                         ret = -EIO;
3179         } else {
3180                 unlock_buffer(bh);
3181         }
3182         return ret;
3183 }
3184 EXPORT_SYMBOL(__sync_dirty_buffer);
3185 
3186 int sync_dirty_buffer(struct buffer_head *bh)
3187 {
3188         return __sync_dirty_buffer(bh, REQ_SYNC);
3189 }
3190 EXPORT_SYMBOL(sync_dirty_buffer);
3191 
3192 /*
3193  * try_to_free_buffers() checks if all the buffers on this particular page
3194  * are unused, and releases them if so.
3195  *
3196  * Exclusion against try_to_free_buffers may be obtained by either
3197  * locking the page or by holding its mapping's private_lock.
3198  *
3199  * If the page is dirty but all the buffers are clean then we need to
3200  * be sure to mark the page clean as well.  This is because the page
3201  * may be against a block device, and a later reattachment of buffers
3202  * to a dirty page will set *all* buffers dirty.  Which would corrupt
3203  * filesystem data on the same device.
3204  *
3205  * The same applies to regular filesystem pages: if all the buffers are
3206  * clean then we set the page clean and proceed.  To do that, we require
3207  * total exclusion from __set_page_dirty_buffers().  That is obtained with
3208  * private_lock.
3209  *
3210  * try_to_free_buffers() is non-blocking.
3211  */
3212 static inline int buffer_busy(struct buffer_head *bh)
3213 {
3214         return atomic_read(&bh->b_count) |
3215                 (bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3216 }
3217 
3218 static int
3219 drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
3220 {
3221         struct buffer_head *head = page_buffers(page);
3222         struct buffer_head *bh;
3223 
3224         bh = head;
3225         do {
3226                 if (buffer_busy(bh))
3227                         goto failed;
3228                 bh = bh->b_this_page;
3229         } while (bh != head);
3230 
3231         do {
3232                 struct buffer_head *next = bh->b_this_page;
3233 
3234                 if (bh->b_assoc_map)
3235                         __remove_assoc_queue(bh);
3236                 bh = next;
3237         } while (bh != head);
3238         *buffers_to_free = head;
3239         __clear_page_buffers(page);
3240         return 1;
3241 failed:
3242         return 0;
3243 }
3244 
3245 int try_to_free_buffers(struct page *page)
3246 {
3247         struct address_space * const mapping = page->mapping;
3248         struct buffer_head *buffers_to_free = NULL;
3249         int ret = 0;
3250 
3251         BUG_ON(!PageLocked(page));
3252         if (PageWriteback(page))
3253                 return 0;
3254 
3255         if (mapping == NULL) {          /* can this still happen? */
3256                 ret = drop_buffers(page, &buffers_to_free);
3257                 goto out;
3258         }
3259 
3260         spin_lock(&mapping->private_lock);
3261         ret = drop_buffers(page, &buffers_to_free);
3262 
3263         /*
3264          * If the filesystem writes its buffers by hand (eg ext3)
3265          * then we can have clean buffers against a dirty page.  We
3266          * clean the page here; otherwise the VM will never notice
3267          * that the filesystem did any IO at all.
3268          *
3269          * Also, during truncate, discard_buffer will have marked all
3270          * the page's buffers clean.  We discover that here and clean
3271          * the page also.
3272          *
3273          * private_lock must be held over this entire operation in order
3274          * to synchronise against __set_page_dirty_buffers and prevent the
3275          * dirty bit from being lost.
3276          */
3277         if (ret)
3278                 cancel_dirty_page(page);
3279         spin_unlock(&mapping->private_lock);
3280 out:
3281         if (buffers_to_free) {
3282                 struct buffer_head *bh = buffers_to_free;
3283 
3284                 do {
3285                         struct buffer_head *next = bh->b_this_page;
3286                         free_buffer_head(bh);
3287                         bh = next;
3288                 } while (bh != buffers_to_free);
3289         }
3290         return ret;
3291 }
3292 EXPORT_SYMBOL(try_to_free_buffers);
3293 
3294 /*
3295  * There are no bdflush tunables left.  But distributions are
3296  * still running obsolete flush daemons, so we terminate them here.
3297  *
3298  * Use of bdflush() is deprecated and will be removed in a future kernel.
3299  * The `flush-X' kernel threads fully replace bdflush daemons and this call.
3300  */
3301 SYSCALL_DEFINE2(bdflush, int, func, long, data)
3302 {
3303         static int msg_count;
3304 
3305         if (!capable(CAP_SYS_ADMIN))
3306                 return -EPERM;
3307 
3308         if (msg_count < 5) {
3309                 msg_count++;
3310                 printk(KERN_INFO
3311                         "warning: process `%s' used the obsolete bdflush"
3312                         " system call\n", current->comm);
3313                 printk(KERN_INFO "Fix your initscripts?\n");
3314         }
3315 
3316         if (func == 1)
3317                 do_exit(0);
3318         return 0;
3319 }
3320 
3321 /*
3322  * Buffer-head allocation
3323  */
3324 static struct kmem_cache *bh_cachep __read_mostly;
3325 
3326 /*
3327  * Once the number of bh's in the machine exceeds this level, we start
3328  * stripping them in writeback.
3329  */
3330 static unsigned long max_buffer_heads;
3331 
3332 int buffer_heads_over_limit;
3333 
3334 struct bh_accounting {
3335         int nr;                 /* Number of live bh's */
3336         int ratelimit;          /* Limit cacheline bouncing */
3337 };
3338 
3339 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3340 
3341 static void recalc_bh_state(void)
3342 {
3343         int i;
3344         int tot = 0;
3345 
3346         if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3347                 return;
3348         __this_cpu_write(bh_accounting.ratelimit, 0);
3349         for_each_online_cpu(i)
3350                 tot += per_cpu(bh_accounting, i).nr;
3351         buffer_heads_over_limit = (tot > max_buffer_heads);
3352 }
3353 
3354 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3355 {
3356         struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3357         if (ret) {
3358                 INIT_LIST_HEAD(&ret->b_assoc_buffers);
3359                 preempt_disable();
3360                 __this_cpu_inc(bh_accounting.nr);
3361                 recalc_bh_state();
3362                 preempt_enable();
3363         }
3364         return ret;
3365 }
3366 EXPORT_SYMBOL(alloc_buffer_head);
3367 
3368 void free_buffer_head(struct buffer_head *bh)
3369 {
3370         BUG_ON(!list_empty(&bh->b_assoc_buffers));
3371         kmem_cache_free(bh_cachep, bh);
3372         preempt_disable();
3373         __this_cpu_dec(bh_accounting.nr);
3374         recalc_bh_state();
3375         preempt_enable();
3376 }
3377 EXPORT_SYMBOL(free_buffer_head);
3378 
3379 static int buffer_exit_cpu_dead(unsigned int cpu)
3380 {
3381         int i;
3382         struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3383 
3384         for (i = 0; i < BH_LRU_SIZE; i++) {
3385                 brelse(b->bhs[i]);
3386                 b->bhs[i] = NULL;
3387         }
3388         this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3389         per_cpu(bh_accounting, cpu).nr = 0;
3390         return 0;
3391 }
3392 
3393 /**
3394  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3395  * @bh: struct buffer_head
3396  *
3397  * Return true if the buffer is up-to-date and false,
3398  * with the buffer locked, if not.
3399  */
3400 int bh_uptodate_or_lock(struct buffer_head *bh)
3401 {
3402         if (!buffer_uptodate(bh)) {
3403                 lock_buffer(bh);
3404                 if (!buffer_uptodate(bh))
3405                         return 0;
3406                 unlock_buffer(bh);
3407         }
3408         return 1;
3409 }
3410 EXPORT_SYMBOL(bh_uptodate_or_lock);
3411 
3412 /**
3413  * bh_submit_read - Submit a locked buffer for reading
3414  * @bh: struct buffer_head
3415  *
3416  * Returns zero on success and -EIO on error.
3417  */
3418 int bh_submit_read(struct buffer_head *bh)
3419 {
3420         BUG_ON(!buffer_locked(bh));
3421 
3422         if (buffer_uptodate(bh)) {
3423                 unlock_buffer(bh);
3424                 return 0;
3425         }
3426 
3427         get_bh(bh);
3428         bh->b_end_io = end_buffer_read_sync;
3429         submit_bh(REQ_OP_READ, 0, bh);
3430         wait_on_buffer(bh);
3431         if (buffer_uptodate(bh))
3432                 return 0;
3433         return -EIO;
3434 }
3435 EXPORT_SYMBOL(bh_submit_read);
3436 
3437 void __init buffer_init(void)
3438 {
3439         unsigned long nrpages;
3440         int ret;
3441 
3442         bh_cachep = kmem_cache_create("buffer_head",
3443                         sizeof(struct buffer_head), 0,
3444                                 (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3445                                 SLAB_MEM_SPREAD),
3446                                 NULL);
3447 
3448         /*
3449          * Limit the bh occupancy to 10% of ZONE_NORMAL
3450          */
3451         nrpages = (nr_free_buffer_pages() * 10) / 100;
3452         max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3453         ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
3454                                         NULL, buffer_exit_cpu_dead);
3455         WARN_ON(ret < 0);
3456 }
/* [<][>][^][v][top][bottom][index][help] */
root/fs/buffer.c

DEFINITIONS
