LXR linux/fs/stack.c

   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 */
  11void 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 PREEMPTION - 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_PREEMPTION 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 PREEMPTION: 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}
  60EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
  61
  62/* copy all attributes */
  63void 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}
  76EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);
  77