Re: [PATCH 0/3] zone-append support in aio and io-uring

[Christoph Hellwig]

On Wed, Jun 17, 2020 at 10:53:36PM +0530, Kanchan Joshi wrote:
> This patchset enables issuing zone-append using aio and io-uring direct-io interface.
> 
> For aio, this introduces opcode IOCB_CMD_ZONE_APPEND. Application uses start LBA
> of the zone to issue append. On completion 'res2' field is used to return
> zone-relative offset.
> 
> For io-uring, this introduces three opcodes: IORING_OP_ZONE_APPEND/APPENDV/APPENDV_FIXED.
> Since io_uring does not have aio-like res2, cqe->flags are repurposed to return zone-relative offset

And what exactly are the semantics supposed to be?  Remember the
unix file abstractions does not know about zones at all.

I really don't think squeezing low-level not quite block storage
protocol details into the Linux read/write path is a good idea.

What could be a useful addition is a way for O_APPEND/RWF_APPEND writes
to report where they actually wrote, as that comes close to Zone Append
while still making sense at our usual abstraction level for file I/O.