Re: [Xen-devel] No graphics with xen pv and Fedora qemu

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/07/16 16:44, Michael Young wrote:
> On Wed, 29 Jun 2016, Michael Young wrote:
>
>> I have been trying to trace a problem when using Fedora's qemu with a
>> pv guest which is that no graphics are available. I get the errors
>>
>> xen be core: xen be: watching backend path (backend/console/2) failed
>> xen be core: xen be: watching backend path (backend/vkbd/2) failed
>> xen be core: xen be: watching backend path (backend/vfb/2) failed
>> xen be core: xen be: watching backend path (backend/qdisk/2) failed
>> xen be core: xen be: watching backend path (backend/qnic/2) failed
>>
>> in the qemu log file in /var/log/xen . So far I have traced it to rbd
>> support in qemu, because qemu-system-i386 built with the
>> --disable-rbd does have working graphics.
>
> I tracked this down eventually. The failure is in tools/xenstore/xs.c
> in xs_watch when it tries to create a read pthread, because the
> initial stack size of 16384 is apparently too small with qemu with rbd
> enabled. I did get it to work if I increased the stack size to 24576.

This is rather curious (and confusing).

I presume this is the xenstore reader thread in qemu which is causing
problems?

The stack size of the reader thread shouldn't need to be big at all, and
I can't see why rbd specifically would cause an issue.  Is there a stack
overflow happening?

~Andrew

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