[RFC PATCH 0/6] dax: Replace bdev_dax_pgoff() with dax_pgoff()

[Vivek Goyal <vgoyal@redhat.com>]

Currently dax code assumes that there is always a block device
associated with it. And block device is passed around in few routines. I
am implementing DAX support for virtiofs and there is no block device
while we are using dax device. So I need dax code to move away from
this assumption that there is always a block device.

We seem to pass around block deivce only to calculate the partition
offset into dax device. bdev_dax_pgoff() does get_start_sect(bdev).

There are two proposed solutions to this problem.

- Get rid of kernel partition support for pmem devices.

- Caller stores offset into dax device and passes that in along with
  dax_device.

First solution was discussed recently in this thread.

https://lore.kernel.org/linux-fsdevel/20200107125159.GA15745@infradead.org/

I feel we already shipped partition support for dax block devices and
going back now will be painful and its easy to break users out there
which are using partitions.

Hence I thought of writing patches for second proposal and see how bad
it looks. To me patches are fairly small and don't break backward 
compatibility and seem like a good step in the direction of removing
dax assumptions about block device.

So I am posting this RFC patch series, which is just boot tested.

Any feedback or comments are welcome.

Thanks
Vivek
 

Vivek Goyal (6):
  dax: Define a helper dax_pgoff() which takes in dax_offset as argument
  dax,iomap,ext4,ext2,xfs: Save dax_offset in "struct iomap"
  fs/dax.c: Start using dax_pgoff() instead of bdev_dax_pgoff()
  dax, dm/md: Use dax_pgoff() instead of bdev_dax_pgoff()
  drivers/dax: Use dax_pgoff() instead of bdev_dax_pgoff()
  dax: Remove bdev_dax_pgoff() helper

 drivers/dax/super.c        | 11 +++++------
 drivers/md/dm-linear.c     |  9 ++++++---
 drivers/md/dm-log-writes.c |  9 ++++++---
 drivers/md/dm-stripe.c     |  8 +++++---
 fs/dax.c                   | 13 ++++++-------
 fs/ext2/inode.c            |  1 +
 fs/ext4/inode.c            |  1 +
 fs/xfs/xfs_iomap.c         |  2 ++
 include/linux/dax.h        |  2 +-
 include/linux/iomap.h      |  1 +
 10 files changed, 34 insertions(+), 23 deletions(-)

-- 
2.20.1
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