fuse: add atomic open+truncate support

This patch allows fuse filesystems to implement open(..., O_TRUNC) as a single
request, instead of separate truncate and open requests.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/fuse.h b/include/linux/fuse.h
index 43a77d73..4360470 100644
--- a/include/linux/fuse.h
+++ b/include/linux/fuse.h
@@ -101,6 +101,7 @@
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
 #define FUSE_FILE_OPS		(1 << 2)
+#define FUSE_ATOMIC_O_TRUNC	(1 << 3)
 
 /**
  * Release flags