Il 24/06/2013 10:13, Stefan Hajnoczi ha scritto:
> On Fri, Jun 21, 2013 at 11:18:42AM +0200, Kevin Wolf wrote:
>> Am 20.06.2013 um 20:20 hat Peter Lieven geschrieben:
>>> @@ -800,6 +801,60 @@ iscsi_getlength(BlockDriverState *bs)
>>> return len;
>>> }
>>>
>>> +static int coroutine_fn iscsi_co_is_allocated(BlockDriverState *bs,
>>> + int64_t sector_num,
>>> + int nb_sectors, int *pnum)
>>> +{
>>> + IscsiLun *iscsilun = bs->opaque;
>>> + struct scsi_task *task = NULL;
>>> + struct scsi_get_lba_status *lbas = NULL;
>>> + struct scsi_lba_status_descriptor *lbasd = NULL;
>>> + int ret;
>>> +
>>> + *pnum = nb_sectors;
>>> +
>>> + if (iscsilun->lbpme == 0) {
>>> + return 1;
>>> + }
>>> +
>>> + /* in-flight requests could invalidate the lba status result */
>>> + while (iscsi_process_flush(iscsilun)) {
>>> + qemu_aio_wait();
>>> + }
>>
>> Note that you're blocking here. The preferred way would be something
>> involving a yield from the coroutine and a reenter as soon as all
>> requests are done. Maybe a CoRwLock does what you need?
>
> The other option is to avoid synchronization here and instead process
> bs->tracked_requests so that any in-flight writes count as allocated.
I think it's a bug if the caller doesn't take into account in-flight
requests. For example mirroring expects writes to mark sectors as
dirty, which will pick up everything that is_allocated fails to pick up.
If all else fails, you can always add a bdrv_drain_all before the query.
Hence, this check is not needed. In fact, raw-posix does not perform it.
Paolo
