mount options for selectively disabling parts of CIFS Unix Extensions

[Steve Langasek]

Hi Steve,

On Mon, Jul 16, 2007 at 10:40:46PM +0000, Steve French wrote:

> I have seen various requests from users to disable part of the CIFS
> Unix Extensions on mount (in some cases fall back to the more
> primitive Windows behavior) but am wondering how far down this line of
> thought I should go ... how many mount options to add to cifs and is
> there a precedent in other file systems.

I've been looking at this exact question recently in relation to some bug
reports in Debian.  The conclusion I reached was that the only thing that's
important for the vast majority of users is to be able to control at mount
time the uid/gid under which the files are exposed to the client system. 
Other than this, I can't think of any cases where users would want their
CIFS mounts to be less Unix-like; I'm surprised that you have users
requesting this.

> Currently negotiating the Unix Extensions (e.g. with a Samba server)
> provides:
> 1) better symlink support
> 2) the real UID/GID/mode can be returned on lookup rather than emulated
>       (even with Unix Extensions negotiated current cifs already does
> allow "uid" and "gid" to be overridden on mount to help with the
> common case in which the server and client's uid's do not match)
> 3) better semantics for byte range locking
> 4) better support posix path names (a few characters like : and *
> would otherwise be reserved)
> 5) better unlink semantics
> 6) faster mkdir
> 7) support for posix acls

And you say in point 2) here that this /is/ possible... but AFAIK that's
not the case with the version of cifs included in linux 2.6.18 or 2.6.21.
Is there a newer version of the cifs kernel code which implements this
support for uid/gid override?

BTW, as far as NFS is concerned, there's certainly support in Linux for
manually specifying an NFS protocol version, and I think things like quotas
and acls are selectable using the standard mount options; and there is an
NFS-specific "nolock" option.  Perhaps those would be worth supporting as
mount options in CIFS as well?  But anything more fine-grained than that is
probably getting a bit silly, IMHO.

Cheers,
-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
vorlon at debian.org                                   http://www.debian.org/