Re: [Qemu-block] [Qemu-devel] [PATCH V3 0/6] ide: avoid main-loop hang on CDROM/NFS failure

[Peter Lieven]

Am 12.11.2015 um 12:33 schrieb Fam Zheng:
> On Fri, 11/06 09:42, Peter Lieven wrote:
> > This series aims at avoiding a hanging main-loop if a vserver has a
> > CDROM image mounted from a NFS share and that NFS share goes down.
> > Typical situation is that users mount an CDROM ISO to install something
> > and then forget to eject that CDROM afterwards.
> > As a consequence this mounted CD is able to bring down the
> > whole vserver if the backend NFS share is unreachable. This is bad
> > especially if the CDROM itself is not needed anymore at this point.
> If a storage backend is lost, would QEMU hang on guest reboot with this patch?
> If so, just for understanding the problem, what is the use case this series
> addresses?

Qemu would hang whenever the next request to the CDROM is made.
This usually happens as soon as the CDROM is mounted (at least in Windows 
guests)
even if there is no CDROM activity intiated by the user. This brings down every 
guest
where the user just forgot to unmount the CDROM just because some NFS storage is
unreachable.

> The code looks good to me apart from the two questions I left, and that I
> didn't fully understand the elementary transfer part.

That indeed is not obvious. There was a long discussion on that topic in V1 of 
this series.

Thanks,
Peter