Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 18 Jun 2020 23:22:58 +0530
From:   Kanchan Joshi <joshi.k@samsung.com>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     axboe@kernel.dk, viro@zeniv.linux.org.uk, bcrl@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-aio@kvack.org, io-uring@vger.kernel.org,
        linux-block@vger.kernel.org, selvakuma.s1@samsung.com,
        nj.shetty@samsung.com, javier.gonz@samsung.com
Subject: Re: [PATCH 0/3] zone-append support in aio and io-uring
Message-ID: <20200618175258.GA4141152@test-zns>
MIME-Version: 1.0
In-Reply-To: <20200618065634.GB24943@infradead.org>
User-Agent: Mutt/1.9.4 (2018-02-28)
Content-Type: multipart/mixed;
        boundary="----LJmyoXw8O9.Ba._wAgamKaSQQ_oizdakYzSktnuewvRJuSc2=_77fd7_"
CMS-TYPE: 105P
References: <CGME20200617172653epcas5p488de50090415eb802e62acc0e23d8812@epcas5p4.samsung.com>
        <1592414619-5646-1-git-send-email-joshi.k@samsung.com>
        <20200618065634.GB24943@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

------LJmyoXw8O9.Ba._wAgamKaSQQ_oizdakYzSktnuewvRJuSc2=_77fd7_
Content-Type: text/plain; charset="utf-8"; format="flowed"
Content-Disposition: inline

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.

------LJmyoXw8O9.Ba._wAgamKaSQQ_oizdakYzSktnuewvRJuSc2=_77fd7_
Content-Type: text/plain; charset="utf-8"


------LJmyoXw8O9.Ba._wAgamKaSQQ_oizdakYzSktnuewvRJuSc2=_77fd7_--