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From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     "hch@infradead.org" <hch@infradead.org>
CC:     Kanchan Joshi <joshiiitr@gmail.com>, Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Kanchan Joshi <joshi.k@samsung.com>,
        "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
        "bcrl@kvack.org" <bcrl@kvack.org>,
        Matthew Wilcox <willy@infradead.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        "io-uring@vger.kernel.org" <io-uring@vger.kernel.org>,
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        "linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
        SelvaKumar S <selvakuma.s1@samsung.com>,
        Nitesh Shetty <nj.shetty@samsung.com>,
        Javier Gonzalez <javier.gonz@samsung.com>
Subject: Re: [PATCH v4 6/6] io_uring: add support for zone-append
Thread-Topic: [PATCH v4 6/6] io_uring: add support for zone-append
Thread-Index: AQHWYdbcc0q15qREKECGO7brHi6zEg==
Date:   Fri, 31 Jul 2020 06:59:45 +0000
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On 2020/07/31 15:45, hch@infradead.org wrote:=0A=
> On Fri, Jul 31, 2020 at 06:42:10AM +0000, Damien Le Moal wrote:=0A=
>>> - We may not be able to use RWF_APPEND, and need exposing a new=0A=
>>> type/flag (RWF_INDIRECT_OFFSET etc.) user-space. Not sure if this=0A=
>>> sounds outrageous, but is it OK to have uring-only flag which can be=0A=
>>> combined with RWF_APPEND?=0A=
>>=0A=
>> Why ? Where is the problem ? O_APPEND/RWF_APPEND is currently meaningles=
s for=0A=
>> raw block device accesses. We could certainly define a meaning for these=
 in the=0A=
>> context of zoned block devices.=0A=
> =0A=
> We can't just add a meaning for O_APPEND on block devices now,=0A=
> as it was previously silently ignored.  I also really don't think any=0A=
> of these semantics even fit the block device to start with.  If you=0A=
> want to work on raw zones use zonefs, that's what is exists for.=0A=
=0A=
Which is fine with me. Just trying to say that I think this is exactly the=
=0A=
discussion we need to start with. What interface do we implement...=0A=
=0A=
Allowing zone append only through zonefs as the raw block device equivalent=
, all=0A=
the O_APPEND/RWF_APPEND semantic is defined and the "return written offset"=
=0A=
implementation in VFS would be common for all file systems, including regul=
ar=0A=
ones. Beside that, there is I think the question of short writes... Not sur=
e if=0A=
short writes can currently happen with async RWF_APPEND writes to regular f=
iles.=0A=
I think not but that may depend on the FS.=0A=
=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=