fs/stack.c

   1 #include <linux/export.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  */
  10 void 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 on 32-bit, we ought to make an effort to keep the two halves of
  25          * i_blocks in sync despite SMP or PREEMPT - though stat's
  26          * generic_fillattr() doesn't bother, and we won't be applying quotas
  27          * (where i_blocks does become important) at the upper level.
  28          *
  29          * We don't actually know what locking is used at the lower level;
  30          * but if it's a filesystem that supports quotas, it will be using
  31          * i_lock as in inode_add_bytes().
  32          */
  33         if (sizeof(i_blocks) > sizeof(long))
  34                 spin_lock(&src->i_lock);
  35         i_blocks = src->i_blocks;
  36         if (sizeof(i_blocks) > sizeof(long))
  37                 spin_unlock(&src->i_lock);
  38
  39         /*
  40          * If CONFIG_SMP or CONFIG_PREEMPT on 32-bit, it's vital for
  41          * fsstack_copy_inode_size() to hold some lock around
  42          * i_size_write(), otherwise i_size_read() may spin forever (see
  43          * include/linux/fs.h).  We don't necessarily hold i_mutex when this
  44          * is called, so take i_lock for that case.
  45          *
  46          * And if on 32-bit, continue our effort to keep the two halves of
  47          * i_blocks in sync despite SMP or PREEMPT: use i_lock  for that case
  48          * too, and do both at once by combining the tests.
  49          *
  50          * There is none of this locking overhead in the 64-bit case.
  51          */
  52         if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
  53                 spin_lock(&dst->i_lock);
  54         i_size_write(dst, i_size);
  55         dst->i_blocks = i_blocks;
  56         if (sizeof(i_size) > sizeof(long) || sizeof(i_blocks) > sizeof(long))
  57                 spin_unlock(&dst->i_lock);
  58 }
  59 EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
  60
  61 /* copy all attributes */
  62 void fsstack_copy_attr_all(struct inode *dest, const struct inode *src)
  63 {
  64         dest->i_mode = src->i_mode;
  65         dest->i_uid = src->i_uid;
  66         dest->i_gid = src->i_gid;
  67         dest->i_rdev = src->i_rdev;
  68         dest->i_atime = src->i_atime;
  69         dest->i_mtime = src->i_mtime;
  70         dest->i_ctime = src->i_ctime;
  71         dest->i_blkbits = src->i_blkbits;
  72         dest->i_flags = src->i_flags;
  73         set_nlink(dest, src->i_nlink);
  74 }
  75 EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);