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  */
  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 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 }
  63 EXPORT_SYMBOL_GPL(fsstack_copy_inode_size);
  64
  65 /* copy all attributes */
  66 void 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 }
  79 EXPORT_SYMBOL_GPL(fsstack_copy_attr_all);