Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN_RANGE operation

[Martin K. Petersen]

Kirill,

> One more thing to discuss. The new REQ_NOZERO flag won't be supported
> by many block devices (their number will be even less, than number of
> REQ_OP_WRITE_ZEROES supporters). Will this be a good thing, in case of
> we will be completing BLKDEV_ZERO_ALLOCATE bios in
> __blkdev_issue_write_zeroes() before splitting? I mean introduction of
> some flag in struct request_queue::limits.  Completion of them with
> -EOPNOTSUPP in block devices drivers looks suboptimal for me.

We already have the NOFALLBACK flag to let the user make that decision.

If that flag is not specified, and I receive an allocate request for a
SCSI device that does not support ANCHOR, my expectation would be that I
would do a regular write same.

If it's a filesystem that is the recipient of the operation and not a
SCSI device, how to react would depend on how the filesystem handles
unwritten extents, etc.

-- 
Martin K. Petersen	Oracle Linux Engineering