Re: [PATCH 1/5] nvme: track subsystems

+static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
+{
+	struct nvme_subsystem *subsys, *found;
+	int ret;
+
+	subsys = kzalloc(sizeof(*subsys), GFP_KERNEL);
+	if (!subsys)
+		return -ENOMEM;
+	ret = ida_simple_get(&nvme_subsystems_ida, 0, 0, GFP_KERNEL);
+	if (ret < 0) {
+		kfree(subsys);
+		return ret;
+	}
+	subsys->instance = ret;
+	mutex_init(&subsys->lock);
+	kref_init(&subsys->ref);
+	INIT_LIST_HEAD(&subsys->ctrls);
+	nvme_init_subnqn(subsys, ctrl, id);
+	memcpy(subsys->serial, id->sn, sizeof(subsys->serial));
+	memcpy(subsys->model, id->mn, sizeof(subsys->model));
+	memcpy(subsys->firmware_rev, id->fr, sizeof(subsys->firmware_rev));
+	subsys->vendor_id = le16_to_cpu(id->vid);
+	subsys->cmic = id->cmic;
+
+	subsys->dev.class = nvme_subsys_class;
+	subsys->dev.release = nvme_release_subsystem;
+	dev_set_name(&subsys->dev, "nvme-subsys%d", subsys->instance);
+	device_initialize(&subsys->dev);
+

Any reason to do all this before we know if we found an existing 
subsystem? Also can the enumeration become with "holes" because you
acquire a subsystem ida temporarily and free it (and another subsystem
just came in)? Not a big issue though...