[PATCH 3/3] xfs: optimize the negative xattr caching

[Christoph Hellwig]

Since the addition of file capabilities every write needs to read xattrs to
check if we have any capabilities to clear.  In Linux 3.0 Andi Kleen added
a flag to cache the fact that we do not have any attributes on an inode.
Make sure to already mark a file as not having any attributes when reading
it from disk in case it doesn't even have an attribute fork.  Based on an
earlier patch from Andi Kleen.

Signed-off-by: Christoph Hellwig <hch at lst.de>

Index: linux-2.6/fs/xfs/linux-2.6/xfs_iops.c
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_iops.c	2011-07-25 23:49:23.011563852 +0200
+++ linux-2.6/fs/xfs/linux-2.6/xfs_iops.c	2011-07-25 23:49:50.281563691 +0200
@@ -1194,9 +1194,14 @@ xfs_setup_inode(
 		break;
 	}
 
-	/* if there is no attribute fork no ACL can exist on this inode */
-	if (!XFS_IFORK_Q(ip))
+	/*
+	 * If there is no attribute fork no ACL can exist on this inode,
+	 * and it can't have any file capabilities attached to it either.
+	 */
+	if (!XFS_IFORK_Q(ip)) {
+		inode_has_no_xattr(inode);
 		cache_no_acl(inode);
+	}
 
 	xfs_iflags_clear(ip, XFS_INEW);
 	barrier();