[PATCH 02/13] libmultipath: Add basic gendisk support

[John Garry]

Add support to allocate and free a multipath gendisk.

NVMe has almost like-for-like equivalents here:
- mpath_alloc_head_disk() -> nvme_mpath_alloc_disk()
- multipath_partition_scan_work() -> nvme_partition_scan_work()
- mpath_remove_disk() -> nvme_remove_head()
- mpath_device_set_live() -> nvme_mpath_set_live()

struct mpath_head_template is introduced as a method for drivers to
provide custom multipath functionality.

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 include/linux/multipath.h |  41 ++++++++++++
 lib/multipath.c           | 129 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 170 insertions(+)

diff --git a/include/linux/multipath.h b/include/linux/multipath.h
index 18cd133b7ca21..be9dd9fb83345 100644
--- a/include/linux/multipath.h
+++ b/include/linux/multipath.h
@@ -5,11 +5,28 @@
 #include <linux/blkdev.h>
 #include <linux/srcu.h>
 
+extern const struct block_device_operations mpath_ops;
+
+struct mpath_disk {
+	struct gendisk		*disk;
+	struct kref		ref;
+	struct work_struct	partition_scan_work;
+	struct mutex		lock;
+	struct mpath_head	*mpath_head;
+	struct device		*parent;
+};
+
 struct mpath_device {
 	struct list_head	siblings;
 	struct gendisk		*disk;
 };
 
+struct mpath_head_template {
+	const struct attribute_group **device_groups;
+};
+
+#define MPATH_HEAD_DISK_LIVE 			0
+
 struct mpath_head {
 	struct srcu_struct	srcu;
 	struct list_head	dev_list;	/* list of all mpath_devs */
@@ -17,12 +34,36 @@ struct mpath_head {
 
 	struct kref		ref;
 
+	unsigned long		flags;
 	struct mpath_device __rcu 		*current_path[MAX_NUMNODES];
+	const struct mpath_head_template	*mpdt;
 	void			*drvdata;
 };
 
+static inline struct mpath_disk *mpath_bd_device_to_disk(struct device *dev)
+{
+	return dev_get_drvdata(dev);
+}
+
+static inline struct mpath_disk *mpath_gendisk_to_disk(struct gendisk *disk)
+{
+	return mpath_bd_device_to_disk(disk_to_dev(disk));
+}
+
 int mpath_get_head(struct mpath_head *mpath_head);
 void mpath_put_head(struct mpath_head *mpath_head);
 struct mpath_head *mpath_alloc_head(void);
+void mpath_put_disk(struct mpath_disk *mpath_disk);
+void mpath_remove_disk(struct mpath_disk *mpath_disk);
+void mpath_unregister_disk(struct mpath_disk *mpath_disk);
+struct mpath_disk *mpath_alloc_head_disk(struct queue_limits *lim,
+			int numa_node);
+void mpath_device_set_live(struct mpath_disk *mpath_disk,
+			struct mpath_device *mpath_device);
+void mpath_unregister_disk(struct mpath_disk *mpath_disk);
 
+static inline bool is_mpath_head(struct gendisk *disk)
+{
+	return disk->fops == &mpath_ops;
+}
 #endif // _LIBMULTIPATH_H
diff --git a/lib/multipath.c b/lib/multipath.c
index 15c495675d729..88efb0ae16acb 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -32,6 +32,135 @@ void mpath_put_head(struct mpath_head *mpath_head)
 }
 EXPORT_SYMBOL_GPL(mpath_put_head);
 
+static void mpath_free_disk(struct kref *ref)
+{
+	struct mpath_disk *mpath_disk =
+		container_of(ref, struct mpath_disk, ref);
+	struct mpath_head *mpath_head = mpath_disk->mpath_head;
+
+	put_disk(mpath_disk->disk);
+	mpath_put_head(mpath_head);
+	kfree(mpath_disk);
+}
+
+void mpath_put_disk(struct mpath_disk *mpath_disk)
+{
+	kref_put(&mpath_disk->ref, mpath_free_disk);
+}
+EXPORT_SYMBOL_GPL(mpath_put_disk);
+
+static int mpath_get_disk(struct mpath_disk *mpath_disk)
+{
+	if (!kref_get_unless_zero(&mpath_disk->ref)) {
+		return -ENXIO;
+	}
+	return 0;
+}
+
+static int mpath_bdev_open(struct gendisk *disk, blk_mode_t mode)
+{
+	struct mpath_disk *mpath_disk = disk->private_data;
+
+	return mpath_get_disk(mpath_disk);
+}
+
+static void mpath_bdev_release(struct gendisk *disk)
+{
+	struct mpath_disk *mpath_disk = disk->private_data;
+
+	mpath_put_disk(mpath_disk);
+}
+
+const struct block_device_operations mpath_ops = {
+	.owner          = THIS_MODULE,
+	.open		= mpath_bdev_open,
+	.release	= mpath_bdev_release,
+};
+EXPORT_SYMBOL_GPL(mpath_ops);
+
+static void multipath_partition_scan_work(struct work_struct *work)
+{
+	struct mpath_disk *mpath_disk =
+		container_of(work, struct mpath_disk, partition_scan_work);
+
+	if (WARN_ON_ONCE(!test_and_clear_bit(GD_SUPPRESS_PART_SCAN,
+					     &mpath_disk->disk->state)))
+		return;
+
+	mutex_lock(&mpath_disk->disk->open_mutex);
+	bdev_disk_changed(mpath_disk->disk, false);
+	mutex_unlock(&mpath_disk->disk->open_mutex);
+}
+
+void mpath_remove_disk(struct mpath_disk *mpath_disk)
+{
+	struct mpath_head *mpath_head = mpath_disk->mpath_head;
+
+	if (test_and_clear_bit(MPATH_HEAD_DISK_LIVE, &mpath_head->flags)) {
+		struct gendisk *disk = mpath_disk->disk;
+
+		del_gendisk(disk);
+	}
+}
+EXPORT_SYMBOL_GPL(mpath_remove_disk);
+
+void mpath_unregister_disk(struct mpath_disk *mpath_disk)
+{
+	mpath_remove_disk(mpath_disk);
+	mpath_put_disk(mpath_disk);
+}
+EXPORT_SYMBOL_GPL(mpath_unregister_disk);
+
+struct mpath_disk *mpath_alloc_head_disk(struct queue_limits *lim, int numa_node)
+{
+	struct mpath_disk *mpath_disk;
+
+	mpath_disk = kzalloc(sizeof(*mpath_disk), GFP_KERNEL);
+	if (!mpath_disk)
+		return NULL;
+
+	INIT_WORK(&mpath_disk->partition_scan_work,
+			multipath_partition_scan_work);
+	mutex_init(&mpath_disk->lock);
+	kref_init(&mpath_disk->ref);
+
+	mpath_disk->disk = blk_alloc_disk(lim, numa_node);
+	if (IS_ERR(mpath_disk->disk)) {
+		kfree(mpath_disk);
+		return NULL;
+	}
+
+	mpath_disk->disk->private_data = mpath_disk;
+	mpath_disk->disk->fops = &mpath_ops;
+
+	set_bit(GD_SUPPRESS_PART_SCAN, &mpath_disk->disk->state);
+
+	return mpath_disk;
+}
+EXPORT_SYMBOL_GPL(mpath_alloc_head_disk);
+
+void mpath_device_set_live(struct mpath_disk *mpath_disk,
+			struct mpath_device *mpath_device)
+{
+	struct mpath_head *mpath_head = mpath_disk->mpath_head;
+	int ret;
+
+	if (!mpath_disk)
+		return;
+
+	if (!test_and_set_bit(MPATH_HEAD_DISK_LIVE, &mpath_head->flags)) {
+		dev_set_drvdata(disk_to_dev(mpath_disk->disk), mpath_disk);
+		ret = device_add_disk(mpath_disk->parent, mpath_disk->disk,
+				mpath_head->mpdt->device_groups);
+		if (ret) {
+			clear_bit(MPATH_HEAD_DISK_LIVE, &mpath_head->flags);
+			return;
+		}
+		queue_work(mpath_wq, &mpath_disk->partition_scan_work);
+	}
+}
+EXPORT_SYMBOL_GPL(mpath_device_set_live);
+
 struct mpath_head *mpath_alloc_head(void)
 {
 	struct mpath_head *mpath_head;
-- 
2.43.5