Hi Naohiro,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[cannot apply to v5.3-rc5 next-20190823]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Naohiro-Aota/btrfs-zoned-block-device-support/20190824-160033
config: x86_64-randconfig-g003-201933 (attached as .config)
compiler: gcc-7 (Debian 7.4.0-10) 7.4.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   fs/btrfs/hmzoned.c: In function 'btrfs_get_dev_zones':
>> fs/btrfs/hmzoned.c:25:8: error: implicit declaration of function 'blkdev_report_zones'; did you mean 'blkdev_nr_zones'? [-Werror=implicit-function-declaration]
     ret = blkdev_report_zones(device->bdev, pos >> SECTOR_SHIFT,
           ^~~~~~~~~~~~~~~~~~~
           blkdev_nr_zones
   cc1: some warnings being treated as errors

vim +25 fs/btrfs/hmzoned.c

    18	
    19	static int btrfs_get_dev_zones(struct btrfs_device *device, u64 pos,
    20				       struct blk_zone *zones,
    21				       unsigned int *nr_zones, gfp_t gfp_mask)
    22	{
    23		int ret;
    24	
  > 25		ret = blkdev_report_zones(device->bdev, pos >> SECTOR_SHIFT,
    26					  zones, nr_zones, gfp_mask);
    27		if (ret != 0) {
    28			btrfs_err_in_rcu(device->fs_info,
    29					 "get zone at %llu on %s failed %d", pos,
    30					 rcu_str_deref(device->name), ret);
    31			return ret;
    32		}
    33		if (!*nr_zones)
    34			return -EIO;
    35	
    36		return 0;
    37	}
    38	

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