Re: [Qemu-devel] [PATCH 3/3] iscsi_truncate: ensure there are no requests in flight

[Paolo Bonzini <pbonzini@redhat.com>]

Il 11/03/2013 11:19, Peter Lieven ha scritto:
> 
> Am 11.03.2013 um 11:16 schrieb Paolo Bonzini <pbonzini@redhat.com>:
> 
>> Il 11/03/2013 11:05, Peter Lieven ha scritto:
>>> ensure that there are no pending I/Os before calling
>>> the sync readcapacity commands. the block_resize monitor
>>> command will also flush all I/O, but double check in
>>> case iscsi_truncate() is called from elsewhere in the
>>> future.
>>>
>>> Signed-off-by: Peter Lieven <pl@kamp.de>
>>> ---
>>> block/iscsi.c |    4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/block/iscsi.c b/block/iscsi.c
>>> index 3d52921..de20d53 100644
>>> --- a/block/iscsi.c
>>> +++ b/block/iscsi.c
>>> @@ -1167,6 +1167,10 @@ static int iscsi_truncate(BlockDriverState *bs,
>>> int64_t offset)
>>>         return -ENOTSUP;
>>>     }
>>>
>>> +    /* ensure all async requests are completed before executing
>>> +     * a sync readcapacity */
>>> +    bdrv_drain_all();
>>> +
>>>     if ((ret = iscsi_readcapacity_sync(iscsilun)) != 0) {
>>>         return ret;
>>>     }
>>
>> NACK to this patch.  It would be a bug, let's fix it properly.
> 
> ok, are you sure that never ever will some new feature call bdrv_truncate() on an iscsi
> device?

I'm sure some new feature _will_ call bdrv_truncate().  But as things
stand now, it would be a bug to do so on an iSCSI device.

For example, qcow1 (and VHDX) will already call it, but that's a bug and
should be fixed otherwise.  Your patch will just cause an assertion failure.

Paolo

> otherwise the real fix would be to implement async read capacity commands like it
> the first patch version for iscsi_truncate().
> 
> Peter
> 
> 
>>
>> The other two are fine, however.
>>
>> Paolo
>