fsetxattr() fails on a writable descriptor?

[Christoph Hellwig]

On Tue, Sep 08, 2009 at 12:29:49PM +0100, P??draig Brady wrote:
> fsetxattr() is failing for me when the permissions are readonly
> but the descriptor is writable as demonstrated by the program below.
> I've tried this on ext3 and ext4 with libattr-2.4.43-3.fc11.i586
> and linux-2.6.30.5-43.fc11.i586

That's not XFS specifci behaviour.  For all xattr operations, fd-based
or not we always do the full permission checks, and have done so since
day one.  Check the routined xattr_permission in fs/xattr.c of the
kernel tree.  It seems a bit unusual, but I'm not sure changing it now
is a good idea - the xattr support has been around for a long time.