[PATCH] cifs: stop trying to use virtual circuits

[Volker Lendecke]

On Mon, Sep 16, 2013 at 11:23:45AM -0400, Jeff Layton wrote:
> Currently, we try to ensure that we use vcnum of 0 on the first
> established session on a connection and then try to use a different
> vcnum on each session after that.
> 
> This is a little odd, since there's no real reason to use a different
> vcnum for each SMB session. I can only assume there was some confusion
> between SMB sessions and VCs. That's somewhat understandable since they
> both get created during SESSION_SETUP, but the documentation indicates
> that they are really orthogonal. The comment on max_vcs in particular
> looks quite misguided. An SMB session is already uniquely identified
> by the SMB UID value -- there's no need to again uniquely ID with a
> VC.
> 
> Furthermore, a vcnum of 0 is a cue to the server that it should release
> any resources that were previously held by the client. This sounds like
> a good thing, until you consider that:
> 
> a) it totally ignores the fact that other programs on the box (e.g.
> smbclient) might have connections established to the server. Using a
> vcnum of 0 causes them to get kicked off.
> 
> b) it causes problems with NAT. If several clients are connected to the
> same server via the same NAT'ed address, whenever one connects to the
> server it kicks off all the others, which then reconnect and kick off
> the first one...ad nauseum.
> 
> I don't see any reason to ignore the advice in "Implementing CIFS" which
> has a comprehensive treatment of virtual circuits. In there, it states
> "...and contrary to the specs the client should always use a VcNumber of
> one, never zero."
> 
> Have the client just use a hardcoded vcnum of 1, and stop abusing the
> special behavior of vcnum 0.

It's kindof a tough choice, but I like this patch. It does
solve real problems. The downside certainly is that we have
worse cleanup behaviour of dead connections, but I would
prefer not killing NATed connections.

Volker

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