Root/fs/stack.c

1#include <linux/module.h>
2#include <linux/fs.h>
3#include <linux/fs_stack.h>
4
5/* does _NOT_ require i_mutex to be held.
6 *
7 * This function cannot be inlined since i_size_{read,write} is rather
8 * heavy-weight on 32-bit systems
9 */
10void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
11{
12    loff_t i_size;
13    blkcnt_t i_blocks;
14
15    /*
16     * i_size_read() includes its own seqlocking and protection from
17     * preemption (see include/linux/fs.h): we need nothing extra for
18     * that here, and prefer to avoid nesting locks than attempt to keep
19     * i_size and i_blocks in sync together.
20     */
21    i_size = i_size_read(src);
22
23    /*
24     * But if CONFIG_LBDAF (on 32-bit), we ought to make an effort to
25     * keep the two halves of i_blocks in sync despite SMP or PREEMPT -
26     * though stat's generic_fillattr() doesn't bother, and we won't be
27     * applying quotas (where i_blocks does become important) at the
28     * 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(). tmpfs uses other locking, and
33     * its 32-bit is (just) able to exceed 2TB i_size with the aid of
34     * holes; but its i_blocks cannot carry into the upper long without
35     * almost 2TB swap - let's ignore that case.
36     */
37    if (sizeof(i_blocks) > sizeof(long))
38        spin_lock(&src->i_lock);
39    i_blocks = src->i_blocks;
40    if (sizeof(i_blocks) > sizeof(long))
41        spin_unlock(&src->i_lock);
42
43    /*
44     * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
45     * fsstack_copy_inode_size() to hold some lock around
46     * i_size_write(), otherwise i_size_read() may spin forever (see
47     * include/linux/fs.h). We don't necessarily hold i_mutex when this
48     * is called, so take i_lock for that case.
49     *
50     * And if CONFIG_LBADF (on 32-bit), continue our effort to keep the
51     * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
52     * for that case too, and do both at once by combining the tests.
53     *
54     * There is none of this locking overhead in the 64-bit case.
55     */
56    if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
57        spin_lock(&dst->i_lock);
58    i_size_write(dst, i_size);
59    dst->i_blocks = i_blocks;
60    if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
61        spin_unlock(&dst->i_lock);
62}
63EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
64
65/* copy all attributes */
66void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
67{
68    dest->i_mode = src->i_mode;
69    dest->i_uid = src->i_uid;
70    dest->i_gid = src->i_gid;
71    dest->i_rdev = src->i_rdev;
72    dest->i_atime = src->i_atime;
73    dest->i_mtime = src->i_mtime;
74    dest->i_ctime = src->i_ctime;
75    dest->i_blkbits = src->i_blkbits;
76    dest->i_flags = src->i_flags;
77    dest->i_nlink = src->i_nlink;
78}
79EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);
80

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