[PATCH 08/13] libmultipath: Add sysfs helpers

[John Garry]

Add helpers for driver sysfs code for the following functionality:
- get/set iopolicy with mpath_iopolicy_store() and mpath_iopolicy_show()
- show device path per NUMA node
- "multipath" attribute group, equivalent to nvme_ns_mpath_attr_group
- device groups attribute array, similar to nvme_ns_attr_groups but not
  containing NVMe members.

Note that mpath_iopolicy_store() has a update callback to allow same
functionality as nvme_subsys_iopolicy_update() be run for clearing paths.

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 include/linux/multipath.h |   9 ++++
 lib/multipath.c           | 110 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+)

diff --git a/include/linux/multipath.h b/include/linux/multipath.h
index f7998de261899..9122560f71778 100644
--- a/include/linux/multipath.h
+++ b/include/linux/multipath.h
@@ -10,6 +10,8 @@
 
 extern const struct file_operations mpath_generic_chr_fops;
 extern const struct block_device_operations mpath_ops;
+extern const struct attribute_group mpath_attr_group;
+extern const struct attribute_group *mpath_device_groups[];
 
 enum mpath_iopolicy_e {
 	MPATH_IOPOLICY_NUMA,
@@ -145,6 +147,13 @@ struct mpath_disk *mpath_alloc_head_disk(struct queue_limits *lim,
 void mpath_device_set_live(struct mpath_disk *mpath_disk,
 			struct mpath_device *mpath_device);
 void mpath_unregister_disk(struct mpath_disk *mpath_disk);
+ssize_t mpath_numa_nodes_show(struct mpath_head *mpath_head,
+			struct mpath_device *mpath_device,
+			struct mpath_iopolicy *iopolicy, char *buf);
+ssize_t mpath_iopolicy_show(struct mpath_iopolicy *mpath_iopolicy, char *buf);
+ssize_t mpath_iopolicy_store(struct mpath_iopolicy *mpath_iopolicy,
+			const char *buf, size_t count,
+			void (*update)(void *data), void *);
 ssize_t mpath_delayed_removal_secs_show(struct mpath_head *mpath_head,
 			char *buf);
 ssize_t mpath_delayed_removal_secs_store(struct mpath_head *mpath_head,
diff --git a/lib/multipath.c b/lib/multipath.c
index 1ce57b9b14d2e..c05b4d25ca223 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -745,6 +745,116 @@ void mpath_device_set_live(struct mpath_disk *mpath_disk,
 }
 EXPORT_SYMBOL_GPL(mpath_device_set_live);
 
+static struct attribute dummy_attr = {
+	.name = "dummy",
+};
+
+static struct attribute *mpath_attrs[] = {
+	&dummy_attr,
+	NULL
+};
+
+static bool multipath_sysfs_group_visible(struct kobject *kobj)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct gendisk *disk = dev_to_disk(dev);
+
+	return is_mpath_head(disk);
+}
+
+static bool multipath_sysfs_attr_visible(struct kobject *kobj,
+		struct attribute *attr, int n)
+{
+	return false;
+}
+
+DEFINE_SYSFS_GROUP_VISIBLE(multipath_sysfs)
+
+const struct attribute_group mpath_attr_group = {
+	.name           = "multipath",
+	.attrs		= mpath_attrs,
+	.is_visible     = SYSFS_GROUP_VISIBLE(multipath_sysfs),
+};
+EXPORT_SYMBOL_GPL(mpath_attr_group);
+
+const struct attribute_group *mpath_device_groups[] = {
+	&mpath_attr_group,
+	NULL
+};
+EXPORT_SYMBOL_GPL(mpath_device_groups);
+
+ssize_t mpath_iopolicy_show(struct mpath_iopolicy *mpath_iopolicy, char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+		mpath_iopolicy_names[mpath_read_iopolicy(mpath_iopolicy)]);
+}
+EXPORT_SYMBOL_GPL(mpath_iopolicy_show);
+
+static void mpath_iopolicy_update(struct mpath_iopolicy *mpath_iopolicy,
+		int iopolicy, void (*update)(void *), void *data)
+{
+	int old_iopolicy = READ_ONCE(mpath_iopolicy->iopolicy);
+
+	if (old_iopolicy == iopolicy)
+		return;
+
+	WRITE_ONCE(mpath_iopolicy->iopolicy, iopolicy);
+
+	/*
+	 * iopolicy changes clear the mpath by design, which @update
+	 * must do.
+	 */
+	update(data);
+
+	pr_err("iopolicy changed from %s to %s\n",
+		mpath_iopolicy_names[old_iopolicy],
+		mpath_iopolicy_names[iopolicy]);
+}
+
+ssize_t mpath_iopolicy_store(struct mpath_iopolicy *mpath_iopolicy,
+				const char *buf, size_t count,
+				void (*update)(void *), void *data)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(mpath_iopolicy_names); i++) {
+		if (sysfs_streq(buf, mpath_iopolicy_names[i])) {
+			mpath_iopolicy_update(mpath_iopolicy, i, update, data);
+			return count;
+		}
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(mpath_iopolicy_store);
+
+ssize_t mpath_numa_nodes_show(struct mpath_head *mpath_head,
+			struct mpath_device *mpath_device,
+			struct mpath_iopolicy *mpath_iopolicy, char *buf)
+{
+	int node, srcu_idx;
+	nodemask_t numa_nodes;
+	struct mpath_device *current_mpath_dev;
+
+	if (mpath_read_iopolicy(mpath_iopolicy) != MPATH_IOPOLICY_NUMA)
+		return 0;
+
+	nodes_clear(numa_nodes);
+
+	srcu_idx = srcu_read_lock(&mpath_head->srcu);
+	for_each_node(node) {
+		current_mpath_dev =
+			srcu_dereference(mpath_head->current_path[node],
+				&mpath_head->srcu);
+		if (current_mpath_dev == mpath_device)
+			node_set(node, numa_nodes);
+	}
+	srcu_read_unlock(&mpath_head->srcu, srcu_idx);
+
+	return sysfs_emit(buf, "%*pbl\n", nodemask_pr_args(&numa_nodes));
+}
+EXPORT_SYMBOL_GPL(mpath_numa_nodes_show);
+
 ssize_t mpath_delayed_removal_secs_show(struct mpath_head *mpath_head,
 					char *buf)
 {
-- 
2.43.5