fs: new API for handling inode->i_version

Add a documentation blob that explains what the i_version field is, how
it is expected to work, and how it is currently implemented by various
filesystems.

We already have inode_inc_iversion. Add several other functions for
manipulating and accessing the i_version counter. For now, the
implementation is trivial and basically works the way that all of the
open-coded i_version accesses work today.

Future patches will convert existing users of i_version to use the new
API, and then convert the backend implementation to do things more
efficiently.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 03102d6..19e72f5 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -18,6 +18,7 @@
 #include <linux/buffer_head.h> /* for inode_has_buffers */
 #include <linux/ratelimit.h>
 #include <linux/list_lru.h>
+#include <linux/iversion.h>
 #include <trace/events/writeback.h>
 #include "internal.h"