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

[Kevin Wolf <kwolf@redhat.com>]

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.

> +
> +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,
};

>  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.

> +    scsi_free_scsi_task(iTask.task);
> +    return ret;
> +
> +fail:
> +    if (iTask.task != NULL) {
> +        scsi_free_scsi_task(iTask.task);
> +    }
> +    *pnum = 0;
> +    return 0;
> +}

Kevin