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

[John Snow <jsnow@redhat.com>]

On 11/13/2015 06:13 AM, Mark Cave-Ayland wrote:
> On 12/11/15 16:30, 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(-)
> 
> Patches 4-6 look like they may handle issues I've found with migration
> in DMA requests on PPC g3beige and mac99 machines. Unfortunately due to
> alignment issues, the macio controller has implement its own versions of
> some of these routines, so should parts of these also be applied
> hw/ide/macio.c aswell?
> 
> 
> ATB,
> 
> Mark.
> 

I still might be suffering delusions that I can sneak this into 2.5 -- I
wouldn't mind reworking this to share with macio later if that's the case.

I don't think I'll make acceptance of this patchset conditional on macio
inclusion either way, though.

--js