scsi: libiscsi: Add helper to calculate max SCSI cmds per session

This patch just breaks out the code that calculates the number of SCSI cmds
that will be used for a SCSI session. It also adds a check that we don't go
over the host's can_queue value.

Link: https://lore.kernel.org/r/20210207044608.27585-6-michael.christie@oracle.com
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/libiscsi.c

@@ -2648,6 +2648,56 @@ void iscsi_pool_free(struct iscsi_pool *q)
 }
 EXPORT_SYMBOL_GPL(iscsi_pool_free);
 
+int iscsi_host_get_max_scsi_cmds(struct Scsi_Host *shost,
+				 uint16_t requested_cmds_max)
+{
+	int scsi_cmds, total_cmds = requested_cmds_max;
+
+check:
+	if (!total_cmds)
+		total_cmds = ISCSI_DEF_XMIT_CMDS_MAX;
+	/*
+	 * The iscsi layer needs some tasks for nop handling and tmfs,
+	 * so the cmds_max must at least be greater than ISCSI_MGMT_CMDS_MAX
+	 * + 1 command for scsi IO.
+	 */
+	if (total_cmds < ISCSI_TOTAL_CMDS_MIN) {
+		printk(KERN_ERR "iscsi: invalid max cmds of %d. Must be a power of two that is at least %d.\n",
+		       total_cmds, ISCSI_TOTAL_CMDS_MIN);
+		return -EINVAL;
+	}
+
+	if (total_cmds > ISCSI_TOTAL_CMDS_MAX) {
+		printk(KERN_INFO "iscsi: invalid max cmds of %d. Must be a power of 2 less than or equal to %d. Using %d.\n",
+		       requested_cmds_max, ISCSI_TOTAL_CMDS_MAX,
+		       ISCSI_TOTAL_CMDS_MAX);
+		total_cmds = ISCSI_TOTAL_CMDS_MAX;
+	}
+
+	if (!is_power_of_2(total_cmds)) {
+		total_cmds = rounddown_pow_of_two(total_cmds);
+		if (total_cmds < ISCSI_TOTAL_CMDS_MIN) {
+			printk(KERN_ERR "iscsi: invalid max cmds of %d. Must be a power of 2 greater than %d.\n", requested_cmds_max, ISCSI_TOTAL_CMDS_MIN);
+			return -EINVAL;
+		}
+
+		printk(KERN_INFO "iscsi: invalid max cmds %d. Must be a power of 2. Rounding max cmds down to %d.\n",
+		       requested_cmds_max, total_cmds);
+	}
+
+	scsi_cmds = total_cmds - ISCSI_MGMT_CMDS_MAX;
+	if (shost->can_queue && scsi_cmds > shost->can_queue) {
+		total_cmds = shost->can_queue;
+
+		printk(KERN_INFO "iscsi: requested max cmds %u is higher than driver limit. Using driver limit %u\n",
+		       requested_cmds_max, shost->can_queue);
+		goto check;
+	}
+
+	return scsi_cmds;
+}
+EXPORT_SYMBOL_GPL(iscsi_host_get_max_scsi_cmds);
+
 /**
  * iscsi_host_add - add host to system
  * @shost: scsi host
@@ -2801,7 +2851,7 @@ iscsi_session_setup(struct iscsi_transport *iscsit, struct Scsi_Host *shost,
 	struct iscsi_host *ihost = shost_priv(shost);
 	struct iscsi_session *session;
 	struct iscsi_cls_session *cls_session;
-	int cmd_i, scsi_cmds, total_cmds = cmds_max;
+	int cmd_i, scsi_cmds;
 	unsigned long flags;
 
 	spin_lock_irqsave(&ihost->lock, flags);
@@ -2812,37 +2862,9 @@ iscsi_session_setup(struct iscsi_transport *iscsit, struct Scsi_Host *shost,
 	ihost->num_sessions++;
 	spin_unlock_irqrestore(&ihost->lock, flags);
 
-	if (!total_cmds)
+	scsi_cmds = iscsi_host_get_max_scsi_cmds(shost, cmds_max);
-		total_cmds = ISCSI_DEF_XMIT_CMDS_MAX;
+	if (scsi_cmds < 0)
-	/*
-	 * The iscsi layer needs some tasks for nop handling and tmfs,
-	 * so the cmds_max must at least be greater than ISCSI_MGMT_CMDS_MAX
-	 * + 1 command for scsi IO.
-	 */
-	if (total_cmds < ISCSI_TOTAL_CMDS_MIN) {
-		printk(KERN_ERR "iscsi: invalid can_queue of %d. can_queue "
-		       "must be a power of two that is at least %d.\n",
-		       total_cmds, ISCSI_TOTAL_CMDS_MIN);
 		goto dec_session_count;
-	}
-
-	if (total_cmds > ISCSI_TOTAL_CMDS_MAX) {
-		printk(KERN_ERR "iscsi: invalid can_queue of %d. can_queue "
-		       "must be a power of 2 less than or equal to %d.\n",
-		       cmds_max, ISCSI_TOTAL_CMDS_MAX);
-		total_cmds = ISCSI_TOTAL_CMDS_MAX;
-	}
-
-	if (!is_power_of_2(total_cmds)) {
-		printk(KERN_ERR "iscsi: invalid can_queue of %d. can_queue "
-		       "must be a power of 2.\n", total_cmds);
-		total_cmds = rounddown_pow_of_two(total_cmds);
-		if (total_cmds < ISCSI_TOTAL_CMDS_MIN)
-			goto dec_session_count;
-		printk(KERN_INFO "iscsi: Rounding can_queue to %d.\n",
-		       total_cmds);
-	}
-	scsi_cmds = total_cmds - ISCSI_MGMT_CMDS_MAX;
 
 	cls_session = iscsi_alloc_session(shost, iscsit,
 					  sizeof(struct iscsi_session) +
@@ -2858,7 +2880,7 @@ iscsi_session_setup(struct iscsi_transport *iscsit, struct Scsi_Host *shost,
 	session->lu_reset_timeout = 15;
 	session->abort_timeout = 10;
 	session->scsi_cmds_max = scsi_cmds;
-	session->cmds_max = total_cmds;
+	session->cmds_max = scsi_cmds + ISCSI_MGMT_CMDS_MAX;
 	session->queued_cmdsn = session->cmdsn = initial_cmdsn;
 	session->exp_cmdsn = initial_cmdsn + 1;
 	session->max_cmdsn = initial_cmdsn + 1;

include/scsi/libiscsi.h

@@ -395,6 +395,8 @@ extern struct Scsi_Host *iscsi_host_alloc(struct scsi_host_template *sht,
 extern void iscsi_host_remove(struct Scsi_Host *shost);
 extern void iscsi_host_free(struct Scsi_Host *shost);
 extern int iscsi_target_alloc(struct scsi_target *starget);
+extern int iscsi_host_get_max_scsi_cmds(struct Scsi_Host *shost,
+					uint16_t requested_cmds_max);
 
 /*
  * session management