[PATCHv2 6/9] libnvme: add support for per-path diagnostic counters

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

Add support for retrieving per-path diagnostic counters such as
command_retry_count, command_error_count, and multipath_failover_count.
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     |  3 +++
 libnvme/src/nvme/private.h |  3 +++
 libnvme/src/nvme/tree.c    | 33 +++++++++++++++++++++++++++++++++
 libnvme/src/nvme/tree.h    | 27 +++++++++++++++++++++++++++
 4 files changed, 66 insertions(+)

diff --git a/libnvme/src/libnvme.ld b/libnvme/src/libnvme.ld
index c32198324..a10629dce 100644
--- a/libnvme/src/libnvme.ld
+++ b/libnvme/src/libnvme.ld
@@ -167,6 +167,9 @@ LIBNVME_3 {
 		nvme_path_get_write_sectors;
 		nvme_path_reset_stat;
 		nvme_path_update_stat;
+		nvme_path_get_command_retry_count;
+		nvme_path_get_command_error_count;
+		nvme_path_get_multipath_failover_count;
 		nvme_random_uuid;
 		nvme_read_config;
 		nvme_read_hostid;
diff --git a/libnvme/src/nvme/private.h b/libnvme/src/nvme/private.h
index f09c0d83f..3d7dfb3c4 100644
--- a/libnvme/src/nvme/private.h
+++ b/libnvme/src/nvme/private.h
@@ -170,6 +170,9 @@ struct nvme_path { /*!generate-accessors*/
 	char *numa_nodes; //!accessors:none
 	int grpid;
 	int queue_depth; //!accessors:none
+	long multipath_failover_count; //!accessors:none
+	long command_retry_count; //!accessors:none
+	long command_error_count; //!accessors:none
 };
 
 struct nvme_ns_head {
diff --git a/libnvme/src/nvme/tree.c b/libnvme/src/nvme/tree.c
index 2949b5cf8..844e18b5c 100644
--- a/libnvme/src/nvme/tree.c
+++ b/libnvme/src/nvme/tree.c
@@ -852,6 +852,39 @@ __public char *nvme_path_get_numa_nodes(nvme_path_t p)
 	return p->numa_nodes;
 }
 
+__public long nvme_path_get_multipath_failover_count(nvme_path_t p)
+{
+	_cleanup_free_ char *failover_count = NULL;
+
+	failover_count = nvme_get_path_attr(p, "multipath_failover_count");
+	if (failover_count)
+		sscanf(failover_count, "%ld", &p->multipath_failover_count);
+
+	return p->multipath_failover_count;
+}
+
+__public long nvme_path_get_command_retry_count(nvme_path_t p)
+{
+	_cleanup_free_ char *retry_count = NULL;
+
+	retry_count = nvme_get_path_attr(p, "command_retry_count");
+	if (retry_count)
+		sscanf(retry_count, "%ld", &p->command_retry_count);
+
+	return p->command_retry_count;
+}
+
+__public long nvme_path_get_command_error_count(nvme_path_t p)
+{
+	_cleanup_free_ char *error_count = NULL;
+
+	error_count = nvme_get_path_attr(p, "command_error_count");
+	if (error_count)
+		sscanf(error_count, "%ld", &p->command_error_count);
+
+	return p->command_error_count;
+}
+
 static nvme_stat_t nvme_path_get_stat(nvme_path_t p, unsigned int idx)
 {
 	if (idx > 1)
diff --git a/libnvme/src/nvme/tree.h b/libnvme/src/nvme/tree.h
index 01f7fda86..4b5d3fd70 100644
--- a/libnvme/src/nvme/tree.h
+++ b/libnvme/src/nvme/tree.h
@@ -704,6 +704,33 @@ char *nvme_path_get_ana_state(nvme_path_t p);
  */
 char *nvme_path_get_numa_nodes(nvme_path_t p);
 
+/**
+ * nvme_path_get_multipath_failover_count() - Get multipath failover count
+ * @p: &nvme_path_t object
+ *
+ * Return: Number of times I/Os have to be failed over to another active path
+ * from path @p maybe due to any transient error observed on path @p
+ */
+long nvme_path_get_multipath_failover_count(nvme_path_t p);
+
+/**
+ * nvme_path_get_command_retry_count() - Get command retry count
+ * @p: &nvme_path_t object
+ *
+ * Return: Number of times any command issued to the namespace represented by
+ * path @p has to be retried
+ */
+long nvme_path_get_command_retry_count(nvme_path_t p);
+
+/**
+ * nvme_path_get_command_error_count() - Get command error count
+ * @p: &nvme_path_t object
+ *
+ * Return: Number of times command issued to the namespace represented by path
+ * @p returns non-zero status or error
+ */
+long nvme_path_get_command_error_count(nvme_path_t p);
+
 /**
  * nvme_path_get_ctrl() - Parent controller of an nvme_path_t object
  * @p:	&nvme_path_t object
-- 
2.53.0