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Re: [libvirt] [PATCH 3/3] Remove wrong check for uml monitor response size

On 16-08-2010 18:08, Eric Blake wrote:
> On 08/16/2010 03:54 AM, Soren Hansen wrote:
>> 09:41:01.134: debug : umlMonitorCommand:698 : Run command 'config con0'
>> 09:41:01.134: debug : umlMonitorCommand:733 : res.error: 6, res.extra: 0, res.length: 4096, res.data:
>> 09:41:01.134: debug : umlMonitorCommand:736 : nbytes: 0
>> 09:41:01.134: debug : umlMonitorCommand:738 : res.error: 0, res.extra: 0, res.length: 4, res.data: pts
>> This one's a kernel. The one where I didn't see the problem is
>> a 2.6.32.something-or-the-other kernel. Mindboggling.
> Oh my.  This really does look like a kernel bug.  Can you confirm it
> with an strace?

Annoyingly, no. It doesn't happen in the primary libvirt thread, so I
have to pass -f to strace, and uml doesn't let you PTRACE it, so I can't
trigger the problem.

> Have you reported this regression to the right kernel folks?

It doesn't happen in 2.6.35, so I seems isolated to that particular
kernel. It's really very, very odd.

> I guess it would help if we could write a simpler test program to
> isolate whether this recvfrom bug exists in a bare minimum number of
> syscalls.  Meanwhile, I have no idea how to work around a buggy recvfrom
> that doesn't return the correct number of bytes.

No, you're right. Whatever we do to work around this is going to suck

Soren Hansen
Ubuntu Developer

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