nvmet: make sn stable once connection was established

Once some host has connected to the target, make sure that the serial
number is stable and cannot be changed.
Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Signed-off-by: Noam Gottlieb <ngottlieb@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/admin-cmd.c

@@ -337,6 +337,12 @@ static void nvmet_execute_identify_ctrl(struct nvmet_req *req)
 	u32 cmd_capsule_size;
 	u16 status = 0;
 
+	if (!subsys->subsys_discovered) {
+		mutex_lock(&subsys->lock);
+		subsys->subsys_discovered = true;
+		mutex_unlock(&subsys->lock);
+	}
+
 	/*
 	 * If there is no model number yet, set it now.  It will then remain
 	 * stable for the life time of the subsystem.

drivers/nvme/target/configfs.c

@@ -1044,12 +1044,18 @@ static ssize_t nvmet_subsys_attr_serial_show(struct config_item *item,
 	return snprintf(page, PAGE_SIZE, "%s\n", subsys->serial);
 }
 
-static ssize_t nvmet_subsys_attr_serial_store(struct config_item *item,
-					      const char *page, size_t count)
+static ssize_t
+nvmet_subsys_attr_serial_store_locked(struct nvmet_subsys *subsys,
+		const char *page, size_t count)
 {
-	struct nvmet_subsys *subsys = to_subsys(item);
 	int pos, len = strcspn(page, "\n");
 
+	if (subsys->subsys_discovered) {
+		pr_err("Can't set serial number. %s is already assigned\n",
+		       subsys->serial);
+		return -EINVAL;
+	}
+
 	if (!len || len > NVMET_SN_MAX_SIZE) {
 		pr_err("Serial Number can not be empty or exceed %d Bytes\n",
 		       NVMET_SN_MAX_SIZE);
@@ -1063,13 +1069,24 @@ static ssize_t nvmet_subsys_attr_serial_store(struct config_item *item,
 		}
 	}
 
+	memcpy_and_pad(subsys->serial, NVMET_SN_MAX_SIZE, page, len, ' ');
+
+	return count;
+}
+
+static ssize_t nvmet_subsys_attr_serial_store(struct config_item *item,
+					      const char *page, size_t count)
+{
+	struct nvmet_subsys *subsys = to_subsys(item);
+	ssize_t ret;
+
 	down_write(&nvmet_config_sem);
 	mutex_lock(&subsys->lock);
-	memcpy_and_pad(subsys->serial, NVMET_SN_MAX_SIZE, page, len, ' ');
+	ret = nvmet_subsys_attr_serial_store_locked(subsys, page, count);
 	mutex_unlock(&subsys->lock);
 	up_write(&nvmet_config_sem);
 
-	return count;
+	return ret;
 }
 CONFIGFS_ATTR(nvmet_subsys_, attr_serial);
 

drivers/nvme/target/nvmet.h

@@ -231,6 +231,7 @@ struct nvmet_subsys {
 
 	u64			ver;
 	char			serial[NVMET_SN_MAX_SIZE];
+	bool			subsys_discovered;
 	char			*subsysnqn;
 	bool			pi_support;