linux-kernel - Re: [PATCH v3 4/4] io_uring: add support for zone-append

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Message-ID: <CA+1E3r+DgR=vVCsUv0cCbPC4MV3Rxfyzee-HWwTogSQ-7F=MoA@mail.gmail.com>
Date:   Mon, 20 Jul 2020 22:32:45 +0530
From:   Kanchan Joshi <joshiiitr@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Kanchan Joshi <joshi.k@...sung.com>,
        viro@...iv.linux.org.uk, bcrl@...ck.org, Damien.LeMoal@....com,
        asml.silence@...il.com, linux-fsdevel@...r.kernel.org,
        "Matias Bj??rling" <mb@...htnvm.io>, linux-kernel@...r.kernel.org,
        linux-aio@...ck.org, io-uring@...r.kernel.org,
        linux-block@...r.kernel.org,
        Selvakumar S <selvakuma.s1@...sung.com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>
Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append

On Fri, Jul 10, 2020 at 7:13 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Fri, Jul 10, 2020 at 06:59:45PM +0530, Kanchan Joshi wrote:
> > > block doesn't work for the case of writes to files that don't have
> > > to be aligned in any way.  And that I think is the more broadly
> > > applicable use case than zone append on block devices.
> >
> > But when can it happen that we do zone-append on a file (zonefs I
> > asssume), and device returns a location (write-pointer essentially)
> > which is not in multiple of 512b?
>
> All the time.  You open a file with O_APPEND.  You write a record to
> it of any kind of size, then the next write will return the position
> it got written at, which can be anything.
I understand if this is about cached write and we are talking about
O_APPEND in general.
But for direct block I/O write and ZoneFS writes, page-cache is not
used, so write(and zone-append result) will be aligned to underlying
block size.
Even though this patchset uses O_APPEND, it filters regular files and
non zoned-block devices by using new FMODE_ZONE_APPEND flag.

-- 
Joshi