[PATCH v2] nvme-multipath: expose path_state via sysfs

[Guixin Liu]

Add a read-only "path_state" sysfs attribute to each NVMe path namespace
device (/sys/class/nvme/nvmeX/nvmeXcYnZ/path_state) that exposes whether
the path is currently enabled or disabled with a specific reason.

The attribute reflects the result of nvme_path_is_disabled() checks:
  - "enabled"                   : path is available for I/O
  - "disabled (ctrl_down)"      : controller is not live/deleting
  - "disabled (ana_pending)"    : ANA state change pending
  - "disabled (ns_not_ready)"   : namespace is not ready

This gives userspace visibility into the multipath path selection state
without requiring users to piece together controller state and namespace
flags manually.

Signed-off-by: Guixin Liu <kanie at linux.alibaba.com>
---
v1->v2:
- Show specific disabled reason instead of just "disabled":
  "disabled (ctrl_down)", "disabled (ana_pending)",
  "disabled (ns_not_ready)". (Nilay Shroff)

 drivers/nvme/host/multipath.c | 16 ++++++++++++++++
 drivers/nvme/host/nvme.h      |  1 +
 drivers/nvme/host/sysfs.c     |  4 +++-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 81fff2f20d23..5e3847fd6632 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -1210,6 +1210,22 @@ static ssize_t in_flight_bytes_show(struct device *dev,
 }
 DEVICE_ATTR_RO(in_flight_bytes);
 
+static ssize_t path_state_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct nvme_ns *ns = nvme_get_ns_from_dev(dev);
+	enum nvme_ctrl_state state = nvme_ctrl_state(ns->ctrl);
+
+	if (state != NVME_CTRL_LIVE && state != NVME_CTRL_DELETING)
+		return sysfs_emit(buf, "disabled (ctrl_down)\n");
+	if (test_bit(NVME_NS_ANA_PENDING, &ns->flags))
+		return sysfs_emit(buf, "disabled (ana_pending)\n");
+	if (!test_bit(NVME_NS_READY, &ns->flags))
+		return sysfs_emit(buf, "disabled (ns_not_ready)\n");
+	return sysfs_emit(buf, "enabled\n");
+}
+DEVICE_ATTR_RO(path_state);
+
 static ssize_t relative_throughput_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 2b2627e0d3ce..bb9b8cdf973a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -1066,6 +1066,7 @@ extern struct device_attribute dev_attr_queue_depth;
 extern struct device_attribute dev_attr_in_flight_bytes;
 extern struct device_attribute dev_attr_relative_throughput;
 extern struct device_attribute dev_attr_numa_nodes;
+extern struct device_attribute dev_attr_path_state;
 extern struct device_attribute dev_attr_delayed_removal_secs;
 extern struct device_attribute subsys_attr_iopolicy;
 
diff --git a/drivers/nvme/host/sysfs.c b/drivers/nvme/host/sysfs.c
index 6309af224c93..5110a3bf5279 100644
--- a/drivers/nvme/host/sysfs.c
+++ b/drivers/nvme/host/sysfs.c
@@ -262,6 +262,7 @@ static struct attribute *nvme_ns_attrs[] = {
 	&dev_attr_in_flight_bytes.attr,
 	&dev_attr_relative_throughput.attr,
 	&dev_attr_numa_nodes.attr,
+	&dev_attr_path_state.attr,
 	&dev_attr_delayed_removal_secs.attr,
 #endif
 	&dev_attr_io_passthru_err_log_enabled.attr,
@@ -296,7 +297,8 @@ static umode_t nvme_ns_attrs_are_visible(struct kobject *kobj,
 			return 0;
 	}
 	if (a == &dev_attr_queue_depth.attr || a == &dev_attr_in_flight_bytes.attr ||
-	    a == &dev_attr_relative_throughput.attr || a == &dev_attr_numa_nodes.attr) {
+	    a == &dev_attr_relative_throughput.attr || a == &dev_attr_numa_nodes.attr ||
+	    a == &dev_attr_path_state.attr) {
 		if (nvme_disk_is_ns_head(dev_to_disk(dev)))
 			return 0;
 	}
-- 
2.43.7