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  */
  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 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 }
  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);