[cifs-protocol] cifs client timeouts and hard/soft mounts

[Shirish Pargaonkar]

On Sat, Dec 4, 2010 at 7:09 AM, Jeff Layton <jlayton at samba.org> wrote:
> On Sat, 4 Dec 2010 06:25:07 -0600
> Shirish Pargaonkar <shirishpargaonkar at gmail.com> wrote:
>
>> On Sat, Dec 4, 2010 at 5:44 AM, Jeff Layton <jlayton at samba.org> wrote:
>>
>> > On Sat, 4 Dec 2010 09:13:21 +0100
>> > Volker Lendecke <Volker.Lendecke at SerNet.DE> wrote:
>> >
>> > > On Fri, Dec 03, 2010 at 09:54:13PM -0600, Christopher R. Hertel wrote:
>> > > > That may seem to be in the "who cares" category, since those old
>> > transports
>> > > > are essentially dead (much more dead than NBT, or even NBF).
>> >  Unfortunately,
>> > > > the code to handle the old transports is still there in Windows, so
>> > there
>> > > > are behaviors -- things like the timeouts you're talking about and the
>> > weird
>> > > > VC=0 shutdown behvior -- that exist because of these old disused
>> > transports.
>> > >
>> > > VC=0, how does Windows treat this facing NAT (masquerading)
>> > > networks? I've done tests in the past where Windows killed
>> > > valid connections from behind a NAT box when a new client
>> > > came in.
>> > >
>> > > Volker
>> >
>> > It seems like the best way to deal with this on the server side with
>> > direct hosted TCP would be to treat VC=0 like any other VC number
>> > (MS-CIFS says that this is allowed).
>> >
>> > Ideally any new connection event from a host however should make the
>> > server check the validity of any other connection from the same host.
>> > That way you could release resources held by dead connections in case
>> > the new one is a reconnect and needs to reclaim state.
>> >
>> > The question is how to check that validity. Unfortunately, the best you
>> > can probably do is rely on TCP keepalives.
>> >
>> > --
>> > Jeff Layton <jlayton at samba.org>
>> >  --
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>> >
>>
>>
>> Is SMB Echo command the only way to determine whether to reconnect or not?
>> The assumption here is SMB server is unresponsive.
>> There could be other circumstances on the server box (or even client box)
>> that are
>> slowing down the SMB server responses such as slow network, slow network
>> stack,
>> memory pressure etc.
>> So server could be fine all along and yet client would ask for reconnection!
>
> I think it's the best mechanism that the protocol has. If we aren't
> going to use SMB echoes to detect an unresponsive server, then what
> would you suggest? I don't think we can make calls wait indefinitely
> for a response without a mechanism to determine when the server is gone
> and attempt to reestablish the connection to it.
>
> --
> Jeff Layton <jlayton at samba.org>
>

I think we should use smb echo command as a means to let users know the
state of mount/server and let them decide.
If smb echo times out, cifs client should just log it and stop at that and a
very next request that receives a response (if any does) should log that server
is responding.