[Libvir] PATCH: Prevent zombie ssh tunnels

[Richard W.M. Jones]

Daniel P. Berrange wrote:
> On Tue, Sep 11, 2007 at 04:56:13AM -0400, Daniel Veillard wrote:
>> On Tue, Sep 11, 2007 at 12:59:59AM +0100, Daniel P. Berrange wrote:
>>> I noticed that when using the SSH tunnel for the remote driver I ended up
>>> with alot of zombie SSH processes. We simply forgot to waitpid() on the
>>> child when a connection attempt failed, or when shutting down an open remote
>>> connection. Attached is a possible patch
>>   Looks fine, like Rich maybe a bit of refactoring might be good. The
>> only worries I have is the following scenario:
>>    - the ssh process dies
>>    - libvirt based application takes some time to notice it
>>    - the OS span a new process with the same PID after a PID rollabck
>>      (not completely unlikely since the ssh may have been started a long
>>      time ago)
>>    - we end-up killing a random process in the system
>>
>> I think this is mostly avoidable by resetting priv->pid to -1 or 0 on 
>> any child communication error, and before doing the kill in the patch.
>> Even better would be to be able to check that the process corresponding
>> to priv->pid is still a child of the current process, I wonder if this
>> can be achieved without blocking with an initial waitpid()
> 
> After some testing I believe we can safely do away with kill() completely.
> If we simply close(priv->sock) which is our end of the socketpair used
> to talk to SSH, then SSH detects the end-of-file condition and exits of
> its on accord. So there's no need to kill() - just close the socket and
> waitpid() seems to do the trickm, unless I'm missing something bad.

+1, but be nicer if that common code was in a function.

Rich.

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