When enabling multipath, if the block device of nvmet is
a nvme_ns_head disk, then we should get the lowlevel block
device to do bio split.

Signed-off-by: Ping Gan <jacky_gam_2001@163.com>
---
 drivers/nvme/host/multipath.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 0a88d7bdc5e3..f6063600e06e 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -371,6 +371,25 @@ static bool nvme_available_path(struct nvme_ns_head *head)
 	return false;
 }
 
+//for polling queue task to get lowlevel block device
+struct block_device *nvme_mpath_get_bdev(struct block_device *bdev)
+{
+	struct nvme_ns_head *head = bdev->bd_disk->private_data;
+	int srcu_idx;
+	struct nvme_ns *ns;
+	struct block_device *ret = NULL;
+
+	if (!multipath)
+		return NULL;
+	srcu_idx = srcu_read_lock(&head->srcu);
+	ns = nvme_find_path(head);
+	if (likely(ns))
+		ret = ns->disk->part0;
+	srcu_read_unlock(&head->srcu, srcu_idx);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(nvme_mpath_get_bdev);
+
 static void nvme_ns_head_submit_bio(struct bio *bio)
 {
 	struct nvme_ns_head *head = bio->bi_bdev->bd_disk->private_data;
@@ -452,6 +471,7 @@ const struct block_device_operations nvme_ns_head_ops = {
 	.report_zones	= nvme_ns_head_report_zones,
 	.pr_ops		= &nvme_pr_ops,
 };
+EXPORT_SYMBOL_GPL(nvme_ns_head_ops);
 
 static inline struct nvme_ns_head *cdev_to_ns_head(struct cdev *cdev)
 {
-- 
2.26.2

Hi Ping,

kernel test robot noticed the following build warnings:

[auto build test WARNING on v6.6-rc1]
[also build test WARNING on linus/master next-20230913]
[cannot apply to hch-configfs/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Ping-Gan/nvmet-Add-nvme-target-polling-queue-task-parameters/20230913-164112
base:   v6.6-rc1
patch link:    https://lore.kernel.org/r/006b6aefe94d73ee64931c769af4a908616439ad.1694592708.git.jacky_gam_2001%40163.com
patch subject: [PATCH 4/4] nvme-core: Get lowlevel disk for target polling queue task
config: m68k-allyesconfig (https://download.01.org/0day-ci/archive/20230913/202309131858.YUV19V9E-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20230913/202309131858.YUV19V9E-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309131858.YUV19V9E-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/nvme/host/multipath.c:375:22: warning: no previous prototype for 'nvme_mpath_get_bdev' [-Wmissing-prototypes]
     375 | struct block_device *nvme_mpath_get_bdev(struct block_device *bdev)
         |                      ^~~~~~~~~~~~~~~~~~~


vim +/nvme_mpath_get_bdev +375 drivers/nvme/host/multipath.c

   373	
   374	//for polling queue task to get lowlevel block device
 > 375	struct block_device *nvme_mpath_get_bdev(struct block_device *bdev)
   376	{
   377		struct nvme_ns_head *head = bdev->bd_disk->private_data;
   378		int srcu_idx;
   379		struct nvme_ns *ns;
   380		struct block_device *ret = NULL;
   381	
   382		if (!multipath)
   383			return NULL;
   384		srcu_idx = srcu_read_lock(&head->srcu);
   385		ns = nvme_find_path(head);
   386		if (likely(ns))
   387			ret = ns->disk->part0;
   388		srcu_read_unlock(&head->srcu, srcu_idx);
   389		return ret;
   390	}
   391	EXPORT_SYMBOL_GPL(nvme_mpath_get_bdev);
   392	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki