nvmet: make discovery NQN configurable

TPAR8013 allows for unique discovery NQNs, so make the discovery
controller NQN configurable by exposing a subsys attribute
'discovery_nqn'.
Signed-off-by: NHannes Reinecke <hare@suse.de>
Reviewed-by: NChaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: NHimanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/target/configfs.c

@@ -1233,6 +1233,44 @@ static ssize_t nvmet_subsys_attr_model_store(struct config_item *item,
 }
 CONFIGFS_ATTR(nvmet_subsys_, attr_model);
 
+static ssize_t nvmet_subsys_attr_discovery_nqn_show(struct config_item *item,
+			char *page)
+{
+	return snprintf(page, PAGE_SIZE, "%s\n",
+			nvmet_disc_subsys->subsysnqn);
+}
+
+static ssize_t nvmet_subsys_attr_discovery_nqn_store(struct config_item *item,
+			const char *page, size_t count)
+{
+	struct nvmet_subsys *subsys = to_subsys(item);
+	char *subsysnqn;
+	int len;
+
+	len = strcspn(page, "\n");
+	if (!len)
+		return -EINVAL;
+
+	subsysnqn = kmemdup_nul(page, len, GFP_KERNEL);
+	if (!subsysnqn)
+		return -ENOMEM;
+
+	/*
+	 * The discovery NQN must be different from subsystem NQN.
+	 */
+	if (!strcmp(subsysnqn, subsys->subsysnqn)) {
+		kfree(subsysnqn);
+		return -EBUSY;
+	}
+	down_write(&nvmet_config_sem);
+	kfree(nvmet_disc_subsys->subsysnqn);
+	nvmet_disc_subsys->subsysnqn = subsysnqn;
+	up_write(&nvmet_config_sem);
+
+	return count;
+}
+CONFIGFS_ATTR(nvmet_subsys_, attr_discovery_nqn);
+
 #ifdef CONFIG_BLK_DEV_INTEGRITY
 static ssize_t nvmet_subsys_attr_pi_enable_show(struct config_item *item,
 						char *page)
@@ -1262,6 +1300,7 @@ static struct configfs_attribute *nvmet_subsys_attrs[] = {
 	&nvmet_subsys_attr_attr_cntlid_min,
 	&nvmet_subsys_attr_attr_cntlid_max,
 	&nvmet_subsys_attr_attr_model,
+	&nvmet_subsys_attr_attr_discovery_nqn,
 #ifdef CONFIG_BLK_DEV_INTEGRITY
 	&nvmet_subsys_attr_attr_pi_enable,
 #endif

drivers/nvme/target/core.c

@@ -1493,7 +1493,8 @@ static struct nvmet_subsys *nvmet_find_get_subsys(struct nvmet_port *port,
 	if (!port)
 		return NULL;
 
-	if (!strcmp(NVME_DISC_SUBSYS_NAME, subsysnqn)) {
+	if (!strcmp(NVME_DISC_SUBSYS_NAME, subsysnqn) ||
+	    !strcmp(nvmet_disc_subsys->subsysnqn, subsysnqn)) {
 		if (!kref_get_unless_zero(&nvmet_disc_subsys->ref))
 			return NULL;
 		return nvmet_disc_subsys;