1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/export.h>
3 #include <linux/fs.h>
4 #include <linux/fs_stack.h>
5
6 /* does _NOT_ require i_mutex to be held.
7 *
8 * This function cannot be inlined since i_size_{read,write} is rather
9 * heavy-weight on 32-bit systems
10 */
11 void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
12 {
13 loff_t i_size;
14 blkcnt_t i_blocks;
15
16 /*
17 * i_size_read() includes its own seqlocking and protection from
18 * preemption (see include/linux/fs.h): we need nothing extra for
19 * that here, and prefer to avoid nesting locks than attempt to keep
20 * i_size and i_blocks in sync together.
21 */
22 i_size = i_size_read(src);
23
24 /*
25 * But on 32-bit, we ought to make an effort to keep the two halves of
26 * i_blocks in sync despite SMP or PREEMPT - though stat's
27 * generic_fillattr() doesn't bother, and we won't be applying quotas
28 * (where i_blocks does become important) at the upper level.
29 *
30 * We don't actually know what locking is used at the lower level;
31 * but if it's a filesystem that supports quotas, it will be using
32 * i_lock as in inode_add_bytes().
33 */
34 if (sizeof(i_blocks) > sizeof(long))
35 spin_lock(&src->i_lock);
36 i_blocks = src->i_blocks;
37 if (sizeof(i_blocks) > sizeof(long))
38 spin_unlock(&src->i_lock);
39
40 /*
41 * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
42 * fsstack_copy_inode_size() to hold some lock around
43 * i_size_write(), otherwise i_size_read() may spin forever (see
44 * include/linux/fs.h). We don't necessarily hold i_mutex when this
45 * is called, so take i_lock for that case.
46 *
47 * And if on 32-bit, continue our effort to keep the two halves of
48 * i_blocks in sync despite SMP or PREEMPT: use i_lock for that case
49 * too, and do both at once by combining the tests.
50 *
51 * There is none of this locking overhead in the 64-bit case.
52 */
53 if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
54 spin_lock(&dst->i_lock);
55 i_size_write(dst, i_size);
56 dst->i_blocks = i_blocks;
57 if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
58 spin_unlock(&dst->i_lock);
59 }
60 EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
61
62 /* copy all attributes */
63 void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
64 {
65 dest->i_mode = src->i_mode;
66 dest->i_uid = src->i_uid;
67 dest->i_gid = src->i_gid;
68 dest->i_rdev = src->i_rdev;
69 dest->i_atime = src->i_atime;
70 dest->i_mtime = src->i_mtime;
71 dest->i_ctime = src->i_ctime;
72 dest->i_blkbits = src->i_blkbits;
73 dest->i_flags = src->i_flags;
74 set_nlink(dest, src->i_nlink);
75 }
76 EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);