[dm-devel] block: Fix a WRITE SAME BUG_ON

[zhangxiaoxu (A)]

On 1/30/2019 10:08 PM, John Dorminy wrote:
> Alternately, could possibly WRITE_SAME bios be accepted with the
> minimum sector size of the stack rather than the max, e.g. 512 in this
> example rather than 4k? They'd need to have a granularity of the
> larger sector size, though, presumabily necessitating new queue limits
> write_same_{granularity,block_size}, which might be too much work. For
> devices with bigger sectors, the block layer or DM would need to
> expand the small-sector payload to an appropriate larger-sector
> payload, but it would preserve the ability to use WRITE_SAME with
> non-zero payloads.
> 
> (I use WRITE_SAME to fill devices with a particular pattern in order
> to catch failures to initialize disk structures appropriately,
> personally, but it's just for convenience/speed.)
I think two LBSs will produce ambiguity.
Reference spec
	Information technology -
	SCSI Block Commands – 4 (SBC-4)
	ISO/IEC 14776-324:201x
	BSR INCITS 506:201x
5.50 WRITE SAME (10) command
The WRITE SAME (10) command (see table 145) requests that the device server
**transfer a single logical block** from the Data-Out Buffer and for each LBA in
the specified range of LBAs: