[PATCHv3] nvmet: implement unique discovery NQN

[Hannes Reinecke <hare@kernel.org>]

From: Hannes Reinecke <hare@suse.de>

Unique discovery NQNs allow to differentiate between discovery
services from (typically physically separate) NVMe-oF subsystems.
This allows to identify discovery connections to the same subsystem
and to minimize the number of discovery connections when
persistent discovery controllers are enabled.
This patch adda a configfs attribute 'discovery_nqn' in the 'nvmet'
configfs directory to specify the unique discovery NQN.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/nvme/target/configfs.c | 46 ++++++++++++++++++++++++++++++++++
 drivers/nvme/target/core.c     |  7 ++++++
 2 files changed, 53 insertions(+)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index d937fe05129e..456aa5e009cd 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -1587,6 +1587,11 @@ static struct config_group *nvmet_subsys_make(struct config_group *group,
 		return ERR_PTR(-EINVAL);
 	}
 
+	if (sysfs_streq(name, nvmet_disc_subsys->subsysnqn)) {
+		pr_err("can't create subsystem using unique discovery NQN\n");
+		return ERR_PTR(-EINVAL);
+	}
+
 	subsys = nvmet_subsys_alloc(name, NVME_NQN_NVME);
 	if (IS_ERR(subsys))
 		return ERR_CAST(subsys);
@@ -2131,7 +2136,48 @@ static const struct config_item_type nvmet_hosts_type = {
 
 static struct config_group nvmet_hosts_group;
 
+static ssize_t nvmet_root_discovery_nqn_show(struct config_item *item,
+					     char *page)
+{
+	return sprintf(page, "%s\n", nvmet_disc_subsys->subsysnqn);
+}
+
+static ssize_t nvmet_root_discovery_nqn_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct list_head *entry;
+	size_t len;
+
+	len = strcspn(page, "\n");
+	if (!len || len > NVMF_NQN_FIELD_LEN - 1)
+		return -EINVAL;
+
+	down_write(&nvmet_config_sem);
+	list_for_each(entry, &nvmet_subsystems_group.cg_children) {
+		struct config_item *item =
+			container_of(entry, struct config_item, ci_entry);
+		if (!strncmp(config_item_name(item), page, len)) {
+			pr_err("duplicate NQN %s\n", config_item_name(item));
+			up_write(&nvmet_config_sem);
+			return -EINVAL;
+		}
+	}
+	memset(nvmet_disc_subsys->subsysnqn, 0, NVMF_NQN_FIELD_LEN);
+	memcpy(nvmet_disc_subsys->subsysnqn, page, len);
+	up_write(&nvmet_config_sem);
+
+	return len;
+}
+
+CONFIGFS_ATTR(nvmet_root_, discovery_nqn);
+
+static struct configfs_attribute *nvmet_root_attrs[] = {
+	&nvmet_root_attr_discovery_nqn,
+	NULL,
+};
+
 static const struct config_item_type nvmet_root_type = {
+	.ct_attrs		= nvmet_root_attrs,
 	.ct_owner		= THIS_MODULE,
 };
 
diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 3935165048e7..9c028bbedb45 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -1530,6 +1530,13 @@ static struct nvmet_subsys *nvmet_find_get_subsys(struct nvmet_port *port,
 	}
 
 	down_read(&nvmet_config_sem);
+	if (!strncmp(nvmet_disc_subsys->subsysnqn, subsysnqn,
+				NVMF_NQN_SIZE)) {
+		if (kref_get_unless_zero(&nvmet_disc_subsys->ref)) {
+			up_read(&nvmet_config_sem);
+			return nvmet_disc_subsys;
+		}
+	}
 	list_for_each_entry(p, &port->subsystems, entry) {
 		if (!strncmp(p->subsys->subsysnqn, subsysnqn,
 				NVMF_NQN_SIZE)) {
-- 
2.35.3