Re: [PATCH RFC v3 04/22] scsi: core: Add support to send reserved commands

Damien Le Moal
2022-10-27T01:21:51Z

On 10/25/22 19:17, John Garry wrote:
> Add a method to queue reserved commands.
>
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
> drivers/scsi/hosts.c | 6 ++++++
> drivers/scsi/scsi_lib.c | 25 +++++++++++++++++++++++++
> include/scsi/scsi_host.h | 1 +
> 3 files changed, 32 insertions(+)
>
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index db89afc37bc9..78968553089f 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -230,6 +230,12 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
> goto fail;
> }
>
> + if (shost->nr_reserved_cmds && !sht->reserved_queuecommand) {
> + shost_printk(KERN_ERR, shost,
> + "nr_reserved_cmds set but no method to queue\n");
> + goto fail;
> + }
> +
> /* Use min_t(int, ...) in case shost->can_queue exceeds SHRT_MAX */
> shost->cmd_per_lun = min_t(int, shost->cmd_per_lun,
> shost->can_queue);
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index a8c4e7c037ae..08015c42c326 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1428,6 +1428,16 @@ static void scsi_complete(struct request *rq)
> struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
> enum scsi_disposition disposition;
>
> + if (blk_mq_is_reserved_rq(rq)) {
> + struct scsi_device *sdev = cmd->device;

This variable is not really needed. You can call:

scsi_device_unbusy(cmd->device, cmd);

No ?

> +
> + scsi_mq_uninit_cmd(cmd);
> + scsi_device_unbusy(sdev, cmd);
> + __blk_mq_end_request(rq, 0);
> +
> + return;
> + }
> +
> INIT_LIST_HEAD(&cmd->eh_entry);
>
> atomic_inc(&cmd->device->iodone_cnt);
> @@ -1718,6 +1728,21 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
> blk_status_t ret;
> int reason;
>
> + if (blk_mq_is_reserved_rq(req)) {
> + if (!(req->rq_flags & RQF_DONTPREP)) {
> + ret = scsi_prepare_cmd(req);
> + if (ret != BLK_STS_OK)
> + goto out_dec_host_busy;
> +
> + req->rq_flags |= RQF_DONTPREP;
> + } else {
> + clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
> + }
> + blk_mq_start_request(req);
> +
> + return shost->hostt->reserved_queuecommand(shost, cmd);
> + }
> +
> WARN_ON_ONCE(cmd->budget_token < 0);
>
> /*
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index 91678c77398e..a39f36aa0b0d 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -73,6 +73,7 @@ struct scsi_host_template {
> * STATUS: REQUIRED
> */
> int (* queuecommand)(struct Scsi_Host *, struct scsi_cmnd *);
> + int (*reserved_queuecommand)(struct Scsi_Host *, struct scsi_cmnd *);

Nit: This op name sound like something returning a bool... May be a
straight "queue_reserved_command" name would be clearer ?

>
> /*
> * The commit_rqs function is used to trigger a hardware

--
Damien Le Moal
Western Digital Research