Re: [Qemu-devel] [PATCHv2 03/11] iscsi: add bdrv_co_is_allocated

[Peter Lieven <pl@kamp.de>]

Am 10.07.2013 11:41, schrieb Kevin Wolf:
> Am 27.06.2013 um 15:11 hat Peter Lieven geschrieben:
>> this patch adds a coroutine for .bdrv_co_is_allocated as well as
>> a generic framework that can be used to build coroutines in block/iscsi.
>>
>> Signed-off-by: Peter Lieven <pl@kamp.de>
>> ---
>>  block/iscsi.c |  123 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 123 insertions(+)
>>
>> diff --git a/block/iscsi.c b/block/iscsi.c
>> index 2e2455d..d31ee95 100644
>> --- a/block/iscsi.c
>> +++ b/block/iscsi.c
>> @@ -58,6 +58,15 @@ typedef struct IscsiLun {
>>      uint32_t max_unmap_bdc;
>>  } IscsiLun;
>>  
>> +typedef struct IscsiTask {
>> +    int status;
>> +    int complete;
>> +    int retries;
>> +    int do_retry;
>> +    struct scsi_task *task;
>> +    Coroutine *co;
>> +} IscsiTask;
>> +
>>  typedef struct IscsiAIOCB {
>>      BlockDriverAIOCB common;
>>      QEMUIOVector *qiov;
>> @@ -113,6 +122,45 @@ iscsi_schedule_bh(IscsiAIOCB *acb)
>>      qemu_bh_schedule(acb->bh);
>>  }
>>  
>> +static void
>> +iscsi_co_generic_cb(struct iscsi_context *iscsi, int status,
>> +                        void *command_data, void *opaque)
>> +{
>> +    struct IscsiTask *iTask = opaque;
>> +    struct scsi_task *task = command_data;
>> +
>> +    iTask->complete = 1;
>> +    iTask->status = status;
>> +    iTask->do_retry = 0;
>> +    iTask->task = task;
>> +
>> +    if (iTask->retries-- > 0 && status == SCSI_STATUS_CHECK_CONDITION
>> +        && task->sense.key == SCSI_SENSE_UNIT_ATTENTION) {
>> +        iTask->do_retry = 1;
>> +        goto out;
>> +    }
>> +
>> +    if (status != SCSI_STATUS_GOOD) {
>> +        error_report("iSCSI: Failure. %s", iscsi_get_error(iscsi));
>> +        goto out;
>> +    }
>> +
>> +out:
>> +    if (iTask->status != SCSI_STATUS_GOOD) {
>> +        scsi_free_scsi_task(iTask->task);
>> +        iTask->task = NULL;
>> +    }
>> +    if (iTask->co) {
>> +        qemu_coroutine_enter(iTask->co, NULL);
>> +    }
>> +}
> In which context does this callback run? If this is from a separate
> thread, you may not do all of this (without even holding the QBL). You
> should probably use a BH to switch to the I/O thread.
good question. the callbacks can only be fired when iscsi_service() is invoked.
this is currently done by registereing iscsi_process_read/write/flush via qemu_aio_set_fd_handler().

so the callbacks are invoked in the aio context it seems. can this be right?
>> +
>> +static void iscsi_co_init_iscsitask(IscsiLun *iscsilun, struct IscsiTask *iTask)
>> +{
>> +    memset(iTask, 0x00, sizeof(struct IscsiTask));
>> +    iTask->co = qemu_coroutine_self();
>> +    iTask->retries = ISCSI_CMD_RETRIES;
>> +}
> Matter of taste, but in my own code I prefer not to have a memset:
>
> *iTask = (struct IscsiTask) {
>     .co         = qemu_coroutine_self(),
>     .retries    = ISCSI_CMD_RETRIES,
> };
ok
>
>>  static void
>>  iscsi_abort_task_cb(struct iscsi_context *iscsi, int status, void *command_data,
>> @@ -807,6 +855,79 @@ 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_get_lba_status *lbas = NULL;
>> +    struct scsi_lba_status_descriptor *lbasd = NULL;
>> +    struct IscsiTask iTask;
>> +    int ret;
>> +
>> +    /* LUN does not support logical block provisioning */
>> +    if (iscsilun->lbpme == 0) {
>> +        *pnum = nb_sectors;
>> +        return 1;
>> +    }
>> +
>> +    iscsi_co_init_iscsitask(iscsilun, &iTask);
>> +
>> +retry:
>> +    if (iscsi_get_lba_status_task(iscsilun->iscsi, iscsilun->lun,
>> +                                  sector_qemu2lun(sector_num, iscsilun),
>> +                                  8 + 16, iscsi_co_generic_cb,
>> +                                  &iTask) == NULL) {
>> +        goto fail;
>> +    }
>> +
>> +    while (!iTask.complete) {
>> +        iscsi_set_events(iscsilun);
>> +        qemu_coroutine_yield();
>> +    }
>> +
>> +    if (iTask.do_retry) {
>> +        goto retry;
>> +    }
>> +
>> +    if (iTask.status != SCSI_STATUS_GOOD) {
>> +        /* 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 */
>> +        *pnum = nb_sectors;
>> +        return 1;
>> +    }
>> +
>> +    lbas = scsi_datain_unmarshall(iTask.task);
>> +    if (lbas == NULL) {
>> +        goto fail;
>> +    }
>> +
>> +    lbasd = &lbas->descriptors[0];
>> +
>> +    if (sector_qemu2lun(sector_num, iscsilun) != lbasd->lba) {
>> +        goto fail;
>> +    }
>> +
>> +    *pnum = lbasd->num_blocks * (iscsilun->block_size / BDRV_SECTOR_SIZE);
>> +    if (*pnum > nb_sectors) {
>> +        *pnum = nb_sectors;
>> +    }
>> +
>> +    ret = lbasd->provisioning == SCSI_PROVISIONING_TYPE_MAPPED ? 1 : 0;
> Wouldn't it be safer to default to allocated, in case new values are
> added in a later protocol version? I agree with returning 0 for both
> unmapped and anchored, though.
agreed.
>
>> +    scsi_free_scsi_task(iTask.task);
>> +    return ret;
>> +
>> +fail:
>> +    if (iTask.task != NULL) {
>> +        scsi_free_scsi_task(iTask.task);
>> +    }
>> +    *pnum = 0;
>> +    return 0;
>> +}
> Kevin
Peter