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Linux/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 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().
 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_PREEMPT 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 CONFIG_LBDAF (on 32-bit), continue our effort to keep the
 48          * two halves of i_blocks in sync despite SMP or PREEMPT: use i_lock
 49          * for that case 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);
 77 

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