Re: [PATCH RFC v2 04/18] scsi: core: Add support to send reserved commands

Damien Le Moal
2022-06-13T07:04:09Z

On 6/9/22 19:29, John Garry wrote:
> Add a method to queue reserved commands.
>
> TODO:
> - fix timeout handler to call into reserved commands
> - We don't clear host_scribble for libata qc, but we should be able to drop
> this if we store libata qc in the scsi cmnd priv_data
>
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
> drivers/scsi/hosts.c | 6 ++++++
> drivers/scsi/scsi_lib.c | 32 ++++++++++++++++++++++++++++++++
> include/scsi/scsi_cmnd.h | 5 +++++
> include/scsi/scsi_host.h | 1 +
> 4 files changed, 44 insertions(+)
>
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index 27296addaf63..5c9b05a8fec8 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -221,6 +221,12 @@ 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;

This would be a driver implementation bug. So what about a WARN() here ?

> + }
> +
> /* 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 f6e53c6d913c..8c8b4c6767d9 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1422,6 +1422,16 @@ static void scsi_complete(struct request *rq)
> struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);
> enum scsi_disposition disposition;
>
> + if (scsi_is_reserved_cmd(cmd)) {
> + struct scsi_device *sdev = cmd->device;
> +
> + 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);
> @@ -1706,6 +1716,28 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
>
> WARN_ON_ONCE(cmd->budget_token < 0);
>
> + if (scsi_is_reserved_cmd(cmd)) {
> + unsigned char *host_scribble = cmd->host_scribble;
> +
> + if (!(req->rq_flags & RQF_DONTPREP)) {
> + ret = scsi_prepare_cmd(req);
> + if (ret != BLK_STS_OK) {
> +

Stray blank line.

> + goto out_dec_host_busy;
> + }

No need for the curly brackets here.

> +
> + req->rq_flags |= RQF_DONTPREP;
> + } else {
> + clear_bit(SCMD_STATE_COMPLETE, &cmd->state);
> + }
> +
> + cmd->host_scribble = host_scribble;
> +
> + blk_mq_start_request(req);
> +
> + return shost->hostt->reserved_queuecommand(shost, cmd);
> + }
> +
> /*
> * If the device is not in running state we will reject some or all
> * commands.
> diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
> index 1e80e70dfa92..e47df5836070 100644
> --- a/include/scsi/scsi_cmnd.h
> +++ b/include/scsi/scsi_cmnd.h
> @@ -152,6 +152,11 @@ static inline void *scsi_cmd_priv(struct scsi_cmnd *cmd)
> return cmd + 1;
> }
>
> +static inline bool scsi_is_reserved_cmd(struct scsi_cmnd *cmd)
> +{
> + return blk_mq_is_reserved_rq(scsi_cmd_to_rq(cmd));
> +}
> +
> void scsi_done(struct scsi_cmnd *cmd);
> void scsi_done_direct(struct scsi_cmnd *cmd);
>
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index 149dcbd4125e..88c8504395c8 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 *);
>
> /*
> * The commit_rqs function is used to trigger a hardware

--
Damien Le Moal
Western Digital Research