libnvme: add support for nshead diagnostic counters

Add support for retrieving nshead diagnostic counters such as requeue_
no_usable_path_count and fail_no_available_path_count.

The requeue_no_usable_path_count counter represents the number of I/Os
requeued to the namespace head when no usable path is available (for
example, due to transient link issues). The fail_no_available_path_count
counter represents the number of I/Os failed when no I/O path is
available (for example, when all paths are removed).

These counters improve visibility into NVMe native multipath behavior
and can be useful for tools such as nvme-top to display real-time
statistics.

Unlike other sysfs attributes, these counters can change dynamically.
Annotate them with "!accessors:none" and provide custom implementations
to always retrieve the latest (non-cached) values.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://patch.msgid.link/20260421145038.3458987-9-nilay@linux.ibm.com
Signed-off-by: Daniel Wagner <wagi@kernel.org>

Author: shroffni

libnvme/src/libnvme.ld

@@ -142,6 +142,8 @@ LIBNVME_3 {
 		libnvme_ns_get_io_ticks;
 		libnvme_ns_get_command_retry_count;
 		libnvme_ns_get_command_error_count;
+		libnvme_ns_get_requeue_no_usable_path_count;
+		libnvme_ns_get_fail_no_available_path_count;
 		libnvme_ns_identify;
 		libnvme_ns_read;
 		libnvme_ns_verify;

libnvme/src/nvme/private.h

@@ -255,8 +255,10 @@ struct libnvme_ns {			// !generate-accessors
 	unsigned char uuid[NVME_UUID_LEN];
 	enum nvme_csi csi;
 
-	long command_retry_count;	// !accessors:none
-	long command_error_count;	// !accessors:none
+	long command_retry_count;		// !accessors:none
+	long command_error_count;		// !accessors:none
+	long requeue_no_usable_path_count;	// !accessors:none
+	long fail_no_available_path_count;	// !accessors:none
 };
 
 struct libnvme_ctrl {			// !generate-accessors

libnvme/src/nvme/tree.c

@@ -2633,6 +2633,28 @@ __public long libnvme_ns_get_command_error_count(libnvme_ns_t n)
 	return n->command_error_count;
 }
 
+__public long libnvme_ns_get_requeue_no_usable_path_count(libnvme_ns_t n)
+{
+	__cleanup_free char *requeue_count = NULL;
+
+	requeue_count = libnvme_get_ns_attr(n, "requeue_no_usable_path_count");
+	if (requeue_count)
+		sscanf(requeue_count, "%ld", &n->requeue_no_usable_path_count);
+
+	return n->requeue_no_usable_path_count;
+}
+
+__public long libnvme_ns_get_fail_no_available_path_count(libnvme_ns_t n)
+{
+	__cleanup_free char *fail_count = NULL;
+
+	fail_count = libnvme_get_ns_attr(n, "fail_no_available_path_count");
+	if (fail_count)
+		sscanf(fail_count, "%ld", &n->fail_no_available_path_count);
+
+	return n->fail_no_available_path_count;
+}
+
 __public int libnvme_ns_identify(libnvme_ns_t n, struct nvme_id_ns *ns)
 {
 	struct libnvme_transport_handle *hdl;

libnvme/src/nvme/tree.h

@@ -527,6 +527,23 @@ long libnvme_ns_get_command_retry_count(libnvme_ns_t n);
  */
 long libnvme_ns_get_command_error_count(libnvme_ns_t n);
 
+/**
+ * libnvme_ns_get_requeue_no_usable_path_count() - Get num of I/O requeue count
+ * @n: &libnvme_ns_t object
+ *
+ * Return: Number of I/Os which are re-queued due to the unavalibility of
+ * any usable path (maybe path is currently experiencing transinet link failure)
+ */
+long libnvme_ns_get_requeue_no_usable_path_count(libnvme_ns_t n);
+
+/**
+ * libnvme_ns_get_fail_no_available_path_count() - Get num of I/Os forced to fail
+ * @n: &libnvme_ns_t object
+ *
+ * Return: Number of I/Os which are forced to fail due to no path available
+ */
+long libnvme_ns_get_fail_no_available_path_count(libnvme_ns_t n);
+
 /**
  * libnvme_ns_get_generic_name() - Returns name of generic namespace chardev.
  * @n:	Namespace instance