[PATCHv2 8/9] libnvme: add support for nshead diagnostic counters

[Nilay Shroff <nilay@linux.ibm.com>]

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>
---
 libnvme/src/libnvme.ld     |  2 ++
 libnvme/src/nvme/private.h |  2 ++
 libnvme/src/nvme/tree.c    | 22 ++++++++++++++++++++++
 libnvme/src/nvme/tree.h    | 17 +++++++++++++++++
 4 files changed, 43 insertions(+)

diff --git a/libnvme/src/libnvme.ld b/libnvme/src/libnvme.ld
index aa24adf59..13bd3995c 100644
--- a/libnvme/src/libnvme.ld
+++ b/libnvme/src/libnvme.ld
@@ -144,6 +144,8 @@ LIBNVME_3 {
 		nvme_ns_get_io_ticks;
 		nvme_ns_get_command_retry_count;
 		nvme_ns_get_command_error_count;
+		nvme_ns_get_requeue_no_usable_path_count;
+		nvme_ns_get_fail_no_available_path_count;
 		nvme_ns_identify;
 		nvme_ns_read;
 		nvme_ns_verify;
diff --git a/libnvme/src/nvme/private.h b/libnvme/src/nvme/private.h
index b2ba1948a..ae0b8507e 100644
--- a/libnvme/src/nvme/private.h
+++ b/libnvme/src/nvme/private.h
@@ -214,6 +214,8 @@ struct nvme_ns { /*!generate-accessors*/
 
 	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 nvme_ctrl { /*!generate-accessors*/
diff --git a/libnvme/src/nvme/tree.c b/libnvme/src/nvme/tree.c
index a8069072d..77aed7eee 100644
--- a/libnvme/src/nvme/tree.c
+++ b/libnvme/src/nvme/tree.c
@@ -2614,6 +2614,28 @@ __public long nvme_ns_get_command_error_count(nvme_ns_t n)
 	return n->command_error_count;
 }
 
+__public long nvme_ns_get_requeue_no_usable_path_count(nvme_ns_t n)
+{
+	_cleanup_free_ char *requeue_count = NULL;
+
+	requeue_count = nvme_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 nvme_ns_get_fail_no_available_path_count(nvme_ns_t n)
+{
+	_cleanup_free_ char *fail_count = NULL;
+
+	fail_count = nvme_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 nvme_ns_identify(nvme_ns_t n, struct nvme_id_ns *ns)
 {
 	struct nvme_transport_handle *hdl;
diff --git a/libnvme/src/nvme/tree.h b/libnvme/src/nvme/tree.h
index ea5dc09a5..e6a26efb1 100644
--- a/libnvme/src/nvme/tree.h
+++ b/libnvme/src/nvme/tree.h
@@ -546,6 +546,23 @@ long nvme_ns_get_command_retry_count(nvme_ns_t n);
  */
 long nvme_ns_get_command_error_count(nvme_ns_t n);
 
+/**
+ * nvme_ns_get_requeue_no_usable_path_count() - Get num of I/O requeue count
+ * @n: &nvme_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 nvme_ns_get_requeue_no_usable_path_count(nvme_ns_t n);
+
+/**
+ * nvme_ns_get_fail_no_available_path_count() - Get num of I/Os forced to fail
+ * @n: &nvme_ns_t object
+ *
+ * Return: Number of I/Os which are forced to fail due to no path available
+ */
+long nvme_ns_get_fail_no_available_path_count(nvme_ns_t n);
+
 /**
  * nvme_ns_get_generic_name() - Returns name of generic namespace chardev.
  * @n:	Namespace instance
-- 
2.53.0