Re: [PATCH v7 0/5] Introduce provisioning primitives

Dave Chinner
2023-06-09T00:10:21Z

On Wed, Jun 07, 2023 at 10:03:40PM -0400, Martin K. Petersen wrote:
>
> Dave,
>
> > Possibly unintentionally, I didn't call it REQ_OP_PROVISION but that's
> > what I intended - the operation does not contain data at all. It's an
> > operation like REQ_OP_DISCARD or REQ_OP_WRITE_ZEROS - it contains a
> > range of sectors that need to be provisioned (or discarded), and
> > nothing else.
>
> Yep. That's also how SCSI defines it. The act of provisioning a block
> range is done through an UNMAP command using a special flag. All it does
> is pin down those LBAs so future writes to them won't result in ENOSPC.

*nod*

That I knew, and it's one of the reasons I'd like the filesystem <->
block layer provisioning model to head in this direction. i.e. we
don't have to do anything special to enable routing of provisioning
requests to hardware and/or remote block storage devices (e.g.
ceph-rbd, nbd, etc). Hence "external" devices can provide the same
guarantees as a native software-only block device implementations
like dm-thinp can provide and everything gets just that little bit
better behaved...

Cheers,

Dave.

--
Dave Chinner
david@fromorbit.com