[libvirt] [BUG?] EAGAIN not triggering error and 'events' gets cleared

Pavel Boldin pboldin at mirantis.com
Tue Apr 28 09:06:00 UTC 2015

Well, actually that seems to be quite a different bug in there.

I will start a new thread.

In short: migration seems to be broken by commit
1a92c719101e5bfa6fe2b78006ad04c7f075ea28. This is because introduced job
_MODIFY waits while MIGRATION_OUT is finished to change `mirrorState'
variable. This deadlocks the libvirt.


On Tue, Apr 28, 2015 at 6:29 AM, Pavel Boldin <pboldin at mirantis.com> wrote:

> Dear Libvirt Developers,
> There seems to be a bug or at least a bad behavior in
> `src/qemu/qemu_monitor.c' lines 683-689 function `qemuMonitorIO':
>             if (qemuMonitorIOWrite(mon) < 0) {
>                 error = true;
>                 if (errno == ECONNRESET)
>                     hangup = true;
>             }
>             events &= ~VIR_EVENT_HANDLE_WRITABLE;
> The `qemuMonitorIOWrite' is returning 0 in case 'write' returns EAGAIN
> thus 'events' is always cleared of `VIR_EVENT_HANDLE_WRITABLE' even in case
> no message have been sent indeed.
> The question is: who is responsible for handling this? It seems like
> 'errno' is getting overwritten inside all of qemuMonitorJSON* functions so
> the caller can't rely on it and it needs to be fixed inside the
> `qemuMonitorIO'.
> Pavel
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