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

[Peter Lieven <pl@kamp.de>]

Am 21.06.2013 19:13, schrieb ronnie sahlberg:
> On Fri, Jun 21, 2013 at 10:06 AM, Peter Lieven <pl@kamp.de> wrote:
>> Am 21.06.2013 18:31, schrieb Paolo Bonzini:
>>> Il 21/06/2013 13:07, Kevin Wolf ha scritto:
>>>>>>>> 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?
>>>>>> Is there a document how to use it? Or can you help here?
>>>> The idea would be to take a read lock while any request is in flight
>>>> (i.e. qemu_co_rwlock_rdlock() before it's started and
>>>> qemu_co_rwlock_unlock() when it completes), and to take a write lock
>>>> (qemu_co_rwlock_wrlock) for the part of iscsi_co_is_allocated() that
>>>> requires that no other request runs in parallel.
>>>>
>>> You can just send the SCSI command asynchronously and wait for the
>>> result.  There is an example in block/qed.c, the same would apply for iscsi.
>> thanks for the pointer paolo, this was i was looking for. this here seems to work:
>>
>> static void
>> iscsi_co_is_allocated_cb(struct iscsi_context *iscsi, int status,
>>                         void *command_data, void *opaque)
>> {
>>     struct IscsiTask *iTask = opaque;
>>     struct scsi_task *task = command_data;
>>     struct scsi_get_lba_status *lbas = NULL;
>>
>>     iTask->complete = 1;
>>
>>     if (status != 0) {
>>         error_report("iSCSI: Failed to get_lba_status on iSCSI lun. %s",
>>                      iscsi_get_error(iscsi));
>>         iTask->status   = 1;
>>         goto out;
>>     }
>>
>>     lbas = scsi_datain_unmarshall(task);
>>     if (lbas == NULL) {
>>         iTask->status   = 1;
>>         goto out;
>>     }
>>
>>     memcpy(&iTask->lbasd, &lbas->descriptors[0],
>>            sizeof(struct scsi_lba_status_descriptor));
> Only the first descriptor?
> sector_num -> sector_num+nb_sectors  could be partially allocated in
> which case you get multiple descriptors.
The number of sectors for which the returned provisioning state
holds true is set in *pnum. If it is only partly allocated the
return value of iscsi_co_is_allocated will be 1 or 0 and pnum
returns the number of sectors for which this is true.
>>     iTask->status   = 0;
>>
>> out:
>>     scsi_free_scsi_task(task);
>>
>>     if (iTask->co) {
>>         qemu_coroutine_enter(iTask->co, NULL);
>>     }
>> }
>>
>> static int coroutine_fn iscsi_co_is_allocated(BlockDriverState *bs,
>>                                               int64_t sector_num,
>>                                               int nb_sectors, int *pnum)
>> {
>>     IscsiLun *iscsilun = bs->opaque;
>>     struct IscsiTask iTask;
>>     int ret;
>>
>>     *pnum = nb_sectors;
>>
>>     if (iscsilun->lbpme == 0) {
>>         return 1;
>>     }
>>
>>     iTask.iscsilun = iscsilun;
>>     iTask.status = 0;
>>     iTask.complete = 0;
>>     iTask.bs = bs;
>>
>>     if (iscsi_get_lba_status_task(iscsilun->iscsi, iscsilun->lun,
>>                                   sector_qemu2lun(sector_num, iscsilun),
>>                                   8 + 16, iscsi_co_is_allocated_cb,
>>                                   &iTask) == NULL) {
>>         *pnum = 0;
>>         return 0;
>>     }
>>
>>     while (!iTask.complete) {
>>         iscsi_set_events(iscsilun);
>>         iTask.co = qemu_coroutine_self();
>>         qemu_coroutine_yield();
>>     }
>>
>>     if (iTask.status != 0) {
>>         /* in case the get_lba_status_callout fails (i.e.
>>          * because the device is busy or the cmd is not
>>          * supported) we pretend all blocks are allocated
>>          * for backwards compatiblity */
>>         return 1;
>>     }
>>
>>     if (sector_qemu2lun(sector_num, iscsilun) != iTask.lbasd.lba) {
>>         *pnum = 0;
>>         return 0;
>>     }
>>
>>     *pnum = iTask.lbasd.num_blocks * (iscsilun->block_size / BDRV_SECTOR_SIZE);
>>     if (*pnum > nb_sectors) {
>>         *pnum = nb_sectors;
>>     }
>>
>>     return (iTask.lbasd.provisioning == SCSI_PROVISIONING_TYPE_MAPPED) ? 1 : 0;
>>
>>     return ret;
>> }