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

[Christoph Hellwig <hch@infradead.org>]

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.