Re: [PATCH v2] ceph: fix posix ACL hooks

[Al Viro <viro@ZenIV.linux.org.uk>]

On Mon, Feb 03, 2014 at 02:29:43AM -0800, Christoph Hellwig wrote:
> On Thu, Jan 30, 2014 at 02:01:38PM -0800, Linus Torvalds wrote:
> > In the end, all the original call-sites should have a dentry, and none
> > of this is "fundamental". But you're right, it looks like an absolute
> > nightmare to add the dentry pointer through the whole chain. Damn.
> > 
> > So I'm not thrilled about it, but maybe that "d_find_alias(inode)" to
> > find the dentry is good enough in practice. It feels very much
> > incorrect (it could find a dentry with a path that you cannot actually
> > access on the server, and result in user-visible errors), but I
> > definitely see your argument. It may just not be worth the pain for
> > this odd ceph case.
> 
> It's not just ceph.  9p fundamentally needs it and I really want to
> convert 9p to the new code so that we can get rid of the lower level
> interfaces entirely and eventually move ACL dispatching entirely
> into the VFS.  The same d_find_alias hack should work for 9p as well,
> although spreading this even more gets uglier and uglier.  Similarly
> for CIFS which pretends to understand the Posix ACL xattrs, but doesn't
> use any of the infrastructure as it seems to rely on server side
> enforcement.

9P is going to be fun to deal with; that's why I've ended up abandoning
vfs.git#experimental-xattr last year.  We probably want to move FIDs
from dentries to inodes there, and rely in ->getxattr() et.al. upon
having already done ->d_revalidate() on some dentry for that inode.

Another pile of fun is fsnotify_xattr() call in __vfs_setxattr_noperm()
and the whole misbegotten IMA/EVM mess ;-/  

See #experimental-xattr - a lot of stuff in that direction is sitting there;
might turn out to be useful.