root/fs/squashfs/file_direct.c

DEFINITIONS

1. squashfs_readpage_block
2. squashfs_read_cache

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (c) 2013
   4  * Phillip Lougher <phillip@squashfs.org.uk>
   5  */
   6 
   7 #include <linux/fs.h>
   8 #include <linux/vfs.h>
   9 #include <linux/kernel.h>
  10 #include <linux/slab.h>
  11 #include <linux/string.h>
  12 #include <linux/pagemap.h>
  13 #include <linux/mutex.h>
  14 
  15 #include "squashfs_fs.h"
  16 #include "squashfs_fs_sb.h"
  17 #include "squashfs_fs_i.h"
  18 #include "squashfs.h"
  19 #include "page_actor.h"
  20 
  21 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
  22         int pages, struct page **page, int bytes);
  23 
  24 /* Read separately compressed datablock directly into page cache */
  25 int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
  26         int expected)
  27 
  28 {
  29         struct inode *inode = target_page->mapping->host;
  30         struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
  31 
  32         int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
  33         int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
  34         int start_index = target_page->index & ~mask;
  35         int end_index = start_index | mask;
  36         int i, n, pages, missing_pages, bytes, res = -ENOMEM;
  37         struct page **page;
  38         struct squashfs_page_actor *actor;
  39         void *pageaddr;
  40 
  41         if (end_index > file_end)
  42                 end_index = file_end;
  43 
  44         pages = end_index - start_index + 1;
  45 
  46         page = kmalloc_array(pages, sizeof(void *), GFP_KERNEL);
  47         if (page == NULL)
  48                 return res;
  49 
  50         /*
  51          * Create a "page actor" which will kmap and kunmap the
  52          * page cache pages appropriately within the decompressor
  53          */
  54         actor = squashfs_page_actor_init_special(page, pages, 0);
  55         if (actor == NULL)
  56                 goto out;
  57 
  58         /* Try to grab all the pages covered by the Squashfs block */
  59         for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
  60                 page[i] = (n == target_page->index) ? target_page :
  61                         grab_cache_page_nowait(target_page->mapping, n);
  62 
  63                 if (page[i] == NULL) {
  64                         missing_pages++;
  65                         continue;
  66                 }
  67 
  68                 if (PageUptodate(page[i])) {
  69                         unlock_page(page[i]);
  70                         put_page(page[i]);
  71                         page[i] = NULL;
  72                         missing_pages++;
  73                 }
  74         }
  75 
  76         if (missing_pages) {
  77                 /*
  78                  * Couldn't get one or more pages, this page has either
  79                  * been VM reclaimed, but others are still in the page cache
  80                  * and uptodate, or we're racing with another thread in
  81                  * squashfs_readpage also trying to grab them.  Fall back to
  82                  * using an intermediate buffer.
  83                  */
  84                 res = squashfs_read_cache(target_page, block, bsize, pages,
  85                                                         page, expected);
  86                 if (res < 0)
  87                         goto mark_errored;
  88 
  89                 goto out;
  90         }
  91 
  92         /* Decompress directly into the page cache buffers */
  93         res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
  94         if (res < 0)
  95                 goto mark_errored;
  96 
  97         if (res != expected) {
  98                 res = -EIO;
  99                 goto mark_errored;
 100         }
 101 
 102         /* Last page may have trailing bytes not filled */
 103         bytes = res % PAGE_SIZE;
 104         if (bytes) {
 105                 pageaddr = kmap_atomic(page[pages - 1]);
 106                 memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
 107                 kunmap_atomic(pageaddr);
 108         }
 109 
 110         /* Mark pages as uptodate, unlock and release */
 111         for (i = 0; i < pages; i++) {
 112                 flush_dcache_page(page[i]);
 113                 SetPageUptodate(page[i]);
 114                 unlock_page(page[i]);
 115                 if (page[i] != target_page)
 116                         put_page(page[i]);
 117         }
 118 
 119         kfree(actor);
 120         kfree(page);
 121 
 122         return 0;
 123 
 124 mark_errored:
 125         /* Decompression failed, mark pages as errored.  Target_page is
 126          * dealt with by the caller
 127          */
 128         for (i = 0; i < pages; i++) {
 129                 if (page[i] == NULL || page[i] == target_page)
 130                         continue;
 131                 flush_dcache_page(page[i]);
 132                 SetPageError(page[i]);
 133                 unlock_page(page[i]);
 134                 put_page(page[i]);
 135         }
 136 
 137 out:
 138         kfree(actor);
 139         kfree(page);
 140         return res;
 141 }
 142 
 143 
 144 static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
 145         int pages, struct page **page, int bytes)
 146 {
 147         struct inode *i = target_page->mapping->host;
 148         struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
 149                                                  block, bsize);
 150         int res = buffer->error, n, offset = 0;
 151 
 152         if (res) {
 153                 ERROR("Unable to read page, block %llx, size %x\n", block,
 154                         bsize);
 155                 goto out;
 156         }
 157 
 158         for (n = 0; n < pages && bytes > 0; n++,
 159                         bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
 160                 int avail = min_t(int, bytes, PAGE_SIZE);
 161 
 162                 if (page[n] == NULL)
 163                         continue;
 164 
 165                 squashfs_fill_page(page[n], buffer, offset, avail);
 166                 unlock_page(page[n]);
 167                 if (page[n] != target_page)
 168                         put_page(page[n]);
 169         }
 170 
 171 out:
 172         squashfs_cache_put(buffer);
 173         return res;
 174 }