Re: [Qemu-devel] [PATCH 1/2] iscsi: add support for bdrv_co_is_allocated()

[Paolo Bonzini <pbonzini@redhat.com>]

Il 21/06/2013 18:06, ronnie sahlberg ha scritto:
> Should we really mix co-routines and AIO in the same backend?
> 
> Would it not be better to instead add a new bdrb_aio_is_allocaed and
> use non-blocking async calls to libiscsi ?

Certainly, but is_allocated's code is not the tidiest.

I'm going to replace the is_allocated callback with a more generic one
(Peter knows, and Kevin might have suspected it too), and I will do the
cleanups at the time I do that.

Paolo

> 
> On Fri, Jun 21, 2013 at 2:18 AM, Kevin Wolf <kwolf@redhat.com> wrote:
>> Am 20.06.2013 um 20:20 hat Peter Lieven geschrieben:
>>> Signed-off-by: Peter Lieven <pl@kamp.de>
>>> ---
>>>  block/iscsi.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 57 insertions(+)
>>>
>>> diff --git a/block/iscsi.c b/block/iscsi.c
>>> index 0bbf0b1..e6b966d 100644
>>> --- a/block/iscsi.c
>>> +++ b/block/iscsi.c
>>> @@ -49,6 +49,7 @@ typedef struct IscsiLun {
>>>      uint64_t num_blocks;
>>>      int events;
>>>      QEMUTimer *nop_timer;
>>> +    uint8_t lbpme;
>>>  } IscsiLun;
>>>
>>>  typedef struct IscsiAIOCB {
>>> @@ -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?
>>
>>> +
>>> +    task = iscsi_get_lba_status_sync(iscsilun->iscsi, iscsilun->lun,
>>> +                                     sector_qemu2lun(sector_num, iscsilun),
>>> +                                     8+16);
>>
>> Spacing around operators (8 + 16)
>>
>>> +
>>> +    if (task == NULL || task->status != SCSI_STATUS_GOOD) {
>>> +        scsi_free_scsi_task(task);
>>> +        return 1;
>>
>> Error cases should set *pnum = 0 and return 0.
>>
>> Kevin
> 
>