Re: [Qemu-devel] [PATCH V4 0/6] ide: avoid main-loop hang on CDROM/NFS failure

[Fam Zheng <famz@redhat.com>]

On Fri, 11/13 17:44, John Snow wrote:
> 
> 
> On 11/12/2015 11:30 AM, 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.
> > 
> > v3->v4: - Patch 1: remove buf argument for cd_read_sector{_sync}
> >         - Patch 1: fix iov_base offset for 2352 sector size
> >         - Patch 2: fix indent [Fam]
> >         - Patch 3: fix leaking of req->iov.iov_base [Fam]
> > 
> > v2->v3: - adressed Stefans comments on Patch 1
> >         - added patches 2,4,5,6
> >         - avoided the term cancel in Patch 3. Added an iovec,
> >           added a BH [Stefan]
> > v1->v2: - fix offset for 2352 byte sector size [Kevin]
> >         - use a sync request if we continue an elementary transfer.
> >           As John pointed out we enter a race condition between next
> >           IDE command and async transfer otherwise. This is sill not
> >           optimal, but it fixes the NFS down problems for all cases where
> >           the NFS server goes down while there is no PIO CD activity.
> >           Of course, it could still happen during a PIO transfer, but I
> >           expect this to be the unlikelier case.
> >           I spent some effort trying to read more sectors at once and
> >           avoiding continuation of elementary transfers, but with
> >           whatever I came up it was destroying migration between different
> >           Qemu versions. I have a quite hackish patch that works and
> >           should survive migration, but I am not happy with it. So I
> >           would like to start with this version as it is a big improvement
> >           already.
> >         - Dropped Patch 5 because it is upstream meanwhile.
> > 
> > Peter Lieven (6):
> >   ide/atapi: make PIO read requests async
> >   block: add blk_abort_aio_request
> >   ide: add support for IDEBufferedRequest
> >   ide: orphan all buffered requests on DMA cancel
> >   ide: enable buffered requests for ATAPI devices
> >   ide: enable buffered requests for PIO read requests
> > 
> >  block/block-backend.c          |  17 +++----
> >  hw/ide/atapi.c                 | 103 +++++++++++++++++++++++++++++++++++------
> >  hw/ide/core.c                  |  51 +++++++++++++++++++-
> >  hw/ide/internal.h              |  14 ++++++
> >  hw/ide/pci.c                   |  19 ++++++++
> >  include/sysemu/block-backend.h |   3 ++
> >  6 files changed, 182 insertions(+), 25 deletions(-)
> > 
> 
> It looks sane to me:
> 
> Reviewed-by: John Snow <jsnow@redhat.com>
> 
> Fam, Stefan: Do you think this is still sane for 2.5? I am inclined to
> get it in as a fix, especially since we've been bouncing it around for
> so long.

I have no objection here, there is no new feature in the series, and guest
hanging right after installing something is admittedly annoying to users.

Thanks,
Fam