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

[John Garry <john.garry@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 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;
+	}
+
 	/* 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) {
+
+				goto out_dec_host_busy;
+			}
+
+			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
-- 
2.26.2