On Mon, Jul 27, 2020 at 12:11:19PM -0700, Ritika Srivastava wrote:

Hence block layer issues write zeroes in blkdev_issue_zeroout()

In response, the storage returns the following SCSI error
Sense Key : Illegal Request [current]
Add. Sense: Invalid command operation code

Once this error is received, the write zero capability of the device is disabled and write_zeroes_max_bytes is set to 0.
DM device queue limits are also set to 0 and device-mapper fails the path.
To avoid this, if BLK_STS_NOTSUPP could be returned, then device-mapper would not fail the paths.

Once the write zero capability has been disabled, blk-lib issues zeroes via __blkdev_issue_zero_pages().

Please let me know if I missed something.

Oh, the stupid SCSI runtime detection case again.  Can you please
document this in a comment?

Also please switch blk_cloned_rq_check_limits to just return the
blk_status_t directly.