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

[Peter Lieven]

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));

    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;
}