dax: Modify bdev_dax_pgoff() to handle NULL bdev

virtiofs does not have a block device but it has dax device.
Modify bdev_dax_pgoff() to be able to handle that.

If there is no bdev, that means dax offset is 0. (It can't be a partition
block device starting at an offset in dax device).

This is little hackish. There have been discussions about getting rid
of dax not supporting partitions.

https://lore.kernel.org/linux-fsdevel/[email protected]/

IMHO, this path can easily break exisitng users. For example
ioctl(BLKPG_ADD_PARTITION) will start breaking on block devices
supporting DAX. Also, I personally find it very useful to be able to
partition dax devices and still be able to use DAX.

Alternatively, I tried to store offset into dax device information in iomap
interface, but that got NACKed.

https://lore.kernel.org/linux-fsdevel/[email protected]/

I can't think of a good path to solve this issue properly. So to make
progress, it seems this patch is least bad option for now and I hope
we can take it.

Signed-off-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Vivek Goyal <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Vishal L Verma <[email protected]>
Cc: "Weiny, Ira" <[email protected]>
Cc: [email protected]
Signed-off-by: Miklos Szeredi <[email protected]>

0 files changed, 0 insertions, 0 deletions