e2fsprogs: Richacl support

[Theodore Ts'o]

On Sun, Oct 18, 2015 at 10:46:23PM +0200, Andreas Gruenbacher wrote:
> > The only question is whether we pay attention to the richacl acl's at
> > all.  One thing that's not clear to me is what VFS is supposed to do
> > if an inode has both an Posix ACL xattr and a Richacl xattr at the
> > same time.
> 
> The VFS will either look for POSIX ACLs or for a richacl; it won't
> even notice if both are present.

How does this work in practice?  Does it look for richacl's first, and
if it doesn't find it, it will then look for a Posix ACL, or vice
versa?

> Right now, filesystems that e2fsck is perfectly happy with can still
> cause errors when used. It would be nice to fix that.
> 
> With POSIX ACLs, this problem is slightly less severe because the ACL
> isn't looked at for the owner; it would even be possible to replace a
> corrupted POSIX ACL. Richacls unfortunately don't allow this
> optimization.

Is there code we can use to verify a richacl, and if it's corrupted,
what are the options about how we can fix it?  Or do we just remove
it, and just use the inode's i_uid field for the owner instead of
whatever might be in the richacl?

Ideally, if you can send the patch to add support to validate / fix
Richacl's in e2fsck, that would be great.

> This really should be a feature flag and not a mount option, it just
> doesn't make sense to switch at mount time.
> 
> From this discussion, I'm even more convinced that we should use an
> incompat feature rather than a ro-incompat feature.

OK, let's go with that.

    	  					- Ted