Re: [PATCH] dax: Arrange for dax_supported check to span multiple devices

[Pankaj Gupta]

> 
> Pankaj reports that starting with commit ad428cdb525a "dax: Check the
> end of the block-device capacity with dax_direct_access()" device-mapper
> no longer allows dax operation. This results from the stricter checks in
> __bdev_dax_supported() that validate that the start and end of a
> block-device map to the same 'pagemap' instance.
> 
> Teach the dax-core and device-mapper to validate the 'pagemap' on a
> per-target basis. This is accomplished by refactoring the
> bdev_dax_supported() internals into generic_fsdax_supported() which
> takes a sector range to validate. Consequently generic_fsdax_supported()
> is suitable to be used in a device-mapper ->iterate_devices() callback.
> A new ->dax_supported() operation is added to allow composite devices to
> split and route upper-level bdev_dax_supported() requests.
> 
> Fixes: ad428cdb525a ("dax: Check the end of the block-device...")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Reported-by: Pankaj Gupta <pagupta@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Thank you for the patch. Looks good to me. 
I also tested the patch and it works well.

Reviewed-and-Tested-by: Pankaj Gupta <pagupta@xxxxxxxxxx> 

Best regards,
Pankaj