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

[Peter Lieven <pl@kamp.de>]

Am 16.11.2015 um 07:17 schrieb Fam Zheng:
> 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.

Thats for speaking for merging it in 2.5. However, I have to clarify that
the fixed behaviour is the same since day 1 of Qemu.

Peter