SMB3 Unix extensions

[Jeremy Allison]

On Fri, Apr 28, 2017 at 12:38:03PM -0500, Steve French wrote:
> On Fri, Apr 28, 2017 at 10:53 AM, Jeremy Allison <jra at samba.org> wrote:
> > On Fri, Apr 28, 2017 at 10:56:28AM +0200, Stefan Metzmacher wrote:
> >> Am 27.04.2017 um 18:13 schrieb Jeremy Allison:
> >> > On Thu, Apr 27, 2017 at 04:36:30PM +0200, Stefan Metzmacher wrote:
> >> >>
> >> >> As far as I remember the idea was to just do this by file handle.
> >> >>
> >> >> So the client will just try to use the create context and the returned
> >> >> create context defines the features available just for that file handle.
> >> >
> >> > Yes, that's right.
> >> >
> >> >> So NO global negotiation anymore!
> >> >
> >> > That was my original idea, but no, we need it. The reason is
> >> > (David Kruse pointed this out) that it allows the client to
> >> > determine if a UNIX create context that is ignored by the server
> >> > is not returned because the server can't grant or doesn't want
> >> > to grant UNIX handles on this part of the file system, vs
> >> > a server that doesn't grant UNIX handles because it doesn't
> >> > implement UNIX extensions.
> >> >
> >> > The initial Negprot extension tells the client that yes,
> >> > I can do UNIX handles I just don't want to for this handle.
> >>
> >> Why does a client need to care about this?
> >> Just avoiding a few bytes for the ignored create context?
> >
> > No, there was a good reason, I just can't remember
> > it right now whilst I'm writing my second SambaXP
> > talk :-).
> >
> > Steve, can you remember the use case ?
> 
> The client needs to know if the server supports Unix Extensions before
> it sends the SMB2 CREATE request so that it doesn't attempt to do an
> unrecoverable
> operation (create supersede/overwrite or delete e.g) which behaves
> differently based
> on whether case sensitive turns out to be supported or not.

Thanks Steve ! I knew there was a unassailable use case here, I just
forgot what it was (deep in writing a VFS presentation right
now :-).