VFS: allow filesystems to implement atomic open+truncate

Add a new attribute flag ATTR_OPEN, with the meaning: "truncation was
initiated by open() due to the O_TRUNC flag".

This way filesystems wanting to implement truncation within their ->open()
method can ignore such truncate requests.

This is a quick & dirty hack, but it comes for free.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Dilger <adilger@clusterfs.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index e3fc5dbb2246..6a4d170ad9a5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -330,6 +330,7 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define ATTR_KILL_SGID  4096
 #define ATTR_FILE       8192
 #define ATTR_KILL_PRIV  16384
+#define ATTR_OPEN       32768   /* Truncating from open(O_TRUNC) */
 
 /*
  * This is the Inode Attributes structure, used for notify_change().  It