Re: [Xen-devel] [PATCH] libxl: Use xenbus to communicate with xenstore if the socket fails

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Thu, 2010-12-09 at 10:53 +0000, Vincent Hanquez wrote:
> On 09/12/10 10:21, Ian Campbell wrote:
> >>   I think there was at least 1 other practical differences, but it
> >> seems to have eluded me.
> 
> Thinking more about it, it might be related to timeout, and/or it might 
> be: If xenstored has decided to not answer you, your thread is dead in 
> the water, because you end up stuck in kernel land forever (wait not 
> interruptible aka D).
> 
> (It might have been related to historical reasons, however it could 
> still be happening in the unlikely event of xenstored dying)

Sounds plausible.

The current driver seems to use wait_event_interruptible and attempt to
do something sane looking with O_NONBLOCK on read but on write looks
like it may end up waiting for a reply forever if xenstored has gone
away, there's even a "FIXME avoid synchronous wait for response" in the
code.

Ian.


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