Messages in this thread | | | Date | Thu, 18 Jun 2020 23:22:58 +0530 | From | Kanchan Joshi <> | Subject | Re: [PATCH 0/3] zone-append support in aio and io-uring |
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On Wed, Jun 17, 2020 at 11:56:34PM -0700, Christoph Hellwig wrote: >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.
I was thinking of raw block-access to zone device rather than pristine file abstraction. And in that context, semantics, at this point, are unchanged (i.e. same as direct writes) while flexibility of async-interface gets added. Synchronous-writes on single-zone sound fine, but synchronous-appends on single-zone do not sound that fine.
>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.
Thanks for suggesting this. O and RWF_APPEND may not go well with block access as end-of-file will be picked from dev inode. But perhaps a new flag like RWF_ZONE_APPEND can help to transform writes (aio or uring) into append without introducing new opcodes. And, I think, this can fit fine on file-abstraction of ZoneFS as well.
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