"killtime" parameter patch ?

[Jeremy Allison]

On Wed, May 16, 2012 at 08:47:34AM +0200, Volker Lendecke wrote:
> On Tue, May 15, 2012 at 05:23:56PM -0700, Jeremy Allison wrote:
> > Interesting situation just came up (original guilty party who
> > raised the issue deleted :-).
> > 
> > Testing a Samba server for reliability. Connected Windows client
> > with open files.
> > 
> > Ethernet cable gets unplugged for a few minutes, client IO fails,
> > then it gets reconnected.
> > 
> > Client reconnects to Samba, gets a new smbd but finds its open files
> > still locked.
> > 
> > "deadtime" doesn't fire because the smbd still has resources open.
> > 
> > Original smbd is still hanging around so sharemode detection finds
> > an open process.
> > 
> > If the files are oplocked oplock break send will get a TCP reset
> > and cause the original smbd to die, but what if the oplock was already
> > broken ?
> > 
> > In that case a "FILE_SHARE_NONE" blocks everything for as long as
> > the original smbd is still around.
> > 
> > Client has no way to signal original server smbd process that it
> > should die.
> > 
> > TCP timeouts will kill after 2 hours but this is considered *way*
> > too long for client to wait. "reset on zero vc" isn't set due to
> > potential NAT issues.
> > 
> > So here is an (untested, but compiles and I think it'll do the job)
> > solution. Parameter "killtime" (set in minutes). If nothing received
> > on a TCP connection (including no SMBecho calls) for "killtime"
> > minutes, it causes the smbd to commit suicide (even with open
> > resources). Cleanly of course :-).
> > 
> > Thoughts on whether this is a good idea ? If so I'll write up the
> > man page :-).
> 
> No, I don't think this is a good idea. We have the keepalive
> and deadtime parameters together with reset on zero vc. You
> can also play with socket options, at least on Linux to
> lower the dead connection detection:
> 
> socket options = SO_KEEPALIVE TCP_KEEPIDLE=120 TCP_KEEPINTVL=10 TCP_KEEPCNT=5
> 
> might be a starting point.
> 
> The big question is -- how does Windows behave? afaik
> Windows has the equivalent of "reset on zero vc" set always.
> 
> One idea for this particular case: What happens if we send a
> netbios keepalive message from server to client when a
> sharing violation is about to happen?

What is really interesting is that we ignore errors from
our own send_keepalive() code.

All that happens if sending a keepalive fails from server
to client is that we log it and stop sending them.

Is that correct ? If we fail in sending a keepalive shouldn't
we terminate in the same way as in the deadtime code ?

That's what the comments suggest, but not what the code
does.

Jeremy.