On 1/25/21 23:55, Shiyang Ruan wrote:

With the support of ->rmap(), it is possible to obtain the superblock on
a mapped device.

If a pmem device is used as one target of mapped device, we cannot
obtain its superblock directly.  With the help of SYSFS, the mapped
device can be found on the target devices.  So, we iterate the
bdev->bd_holder_disks to obtain its mapped device.

Signed-off-by: Shiyang Ruan <redacted>
---
  drivers/md/dm.c       | 61 +++++++++++++++++++++++++++++++++++++++++++
  drivers/nvdimm/pmem.c | 11 +++-----
  fs/block_dev.c        | 42 ++++++++++++++++++++++++++++-
  include/linux/genhd.h |  2 ++
  4 files changed, 107 insertions(+), 9 deletions(-)

I can't see md raid is involved here, perhaps dm-devel need to be cced 
instead of raid list. And the subject need to be changed as well.

Thanks,
Guoqing