[PATCH v3 01/10] nvme-multipath: add initial support for using libmultipath

Add initial support, as follows:
- Add mpath_head_template
- Add mpath_device in nvme_ns
- Add mpath_disk pointer to head structure

Initially all the functionality which mpath_head_template points to will be
unused, until the driver fully switches to libmultipath. Otherwise it's
hard to do so in a step-wise fashion without breaking functionality.

Many of the libmultipath-based function added will reference the
ns mpath_device, so add that now. Also add the NS head disk pointer for the
same reason.

Signed-off-by: John Garry <[email protected]>
---
 drivers/nvme/host/Kconfig     | 1 +
 drivers/nvme/host/multipath.c | 4 ++++
 drivers/nvme/host/nvme.h      | 8 ++++++++
 3 files changed, 13 insertions(+)

diff --git a/drivers/nvme/host/Kconfig b/drivers/nvme/host/Kconfig
index 31974c7dd20c9..1b3f76e781bad 100644
--- a/drivers/nvme/host/Kconfig
+++ b/drivers/nvme/host/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config NVME_CORE
 	tristate
+	select LIBMULTIPATH
 
 config BLK_DEV_NVME
 	tristate "NVM Express block device"
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 9b9a657fa330f..14947736744a5 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -1496,3 +1496,7 @@ void nvme_mpath_uninit(struct nvme_ctrl *ctrl)
 	ctrl->ana_log_buf = NULL;
 	ctrl->ana_log_size = 0;
 }
+
+__maybe_unused
+static const struct mpath_head_template mpdt = {
+};
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 824651cc898db..3e023948015ac 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -13,6 +13,7 @@
 #include <linux/blk-mq.h>
 #include <linux/sed-opal.h>
 #include <linux/fault-inject.h>
+#include <linux/multipath.h>
 #include <linux/rcupdate.h>
 #include <linux/wait.h>
 #include <linux/t10-pi.h>
@@ -560,6 +561,8 @@ struct nvme_ns_head {
 
 	u16			nr_plids;
 	u16			*plids;
+
+	struct mpath_head	mpath_head;
 #ifdef CONFIG_NVME_MULTIPATH
 	struct bio_list		requeue_list;
 	spinlock_t		requeue_lock;
@@ -590,6 +593,7 @@ enum nvme_ns_features {
 };
 
 struct nvme_ns {
+	struct mpath_device mpath_device;
 	struct list_head list;
 
 	struct nvme_ctrl *ctrl;
@@ -620,6 +624,10 @@ struct nvme_ns {
 	struct nvme_fault_inject fault_inject;
 };
 
+#define nvme_mpath_to_ns(d) container_of(d, struct nvme_ns, mpath_device)
+#define nvme_mpath_to_ns_head(h) \
+		container_of(h, struct nvme_ns_head, mpath_head)
+
 /* NVMe ns supports metadata actions by the controller (generate/strip) */
 static inline bool nvme_ns_has_pi(struct nvme_ns_head *head)
 {
-- 
2.43.7