linux-kernel - Re: [PATCH v4 6/6] io_uring: add support for zone-append

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Message-ID: <20220302205151.76f6wfqb2t3llnvf@garbanzo>
Date:   Wed, 2 Mar 2022 12:51:51 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     "hch@...radead.org" <hch@...radead.org>
Cc:     Damien Le Moal <Damien.LeMoal@....com>,
        Kanchan Joshi <joshiiitr@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        Kanchan Joshi <joshi.k@...sung.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "bcrl@...ck.org" <bcrl@...ck.org>,
        Matthew Wilcox <willy@...radead.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-aio@...ck.org" <linux-aio@...ck.org>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        SelvaKumar S <selvakuma.s1@...sung.com>,
        Nitesh Shetty <nj.shetty@...sung.com>,
        Javier Gonzalez <javier.gonz@...sung.com>,
        Adam Manzanares <a.manzanares@...sung.com>,
        "Remzi H. Arpaci-Dusseau" <remzi@...wisc.edu>
Subject: Re: [PATCH v4 6/6] io_uring: add support for zone-append

On Fri, Jul 31, 2020 at 07:45:26AM +0100, hch@...radead.org wrote:
> On Fri, Jul 31, 2020 at 06:42:10AM +0000, Damien Le Moal wrote:
> > > - We may not be able to use RWF_APPEND, and need exposing a new
> > > type/flag (RWF_INDIRECT_OFFSET etc.) user-space. Not sure if this
> > > sounds outrageous, but is it OK to have uring-only flag which can be
> > > combined with RWF_APPEND?
> > 
> > Why ? Where is the problem ? O_APPEND/RWF_APPEND is currently meaningless for
> > raw block device accesses. We could certainly define a meaning for these in the
> > context of zoned block devices.
> 
> We can't just add a meaning for O_APPEND on block devices now,

Make sense.

Is a new call system call for nameless writes called for instead then?
Then there is no baggage. Or is this completely stupid?

> as it was previously silently ignored.  I also really don't think any
> of these semantics even fit the block device to start with.  If you
> want to work on raw zones use zonefs, that's what is exists for.

Using zonefs adds a slight VFS overhead. Fine if we want to live with
that, but I have a feeling if we want to do something like just testing
hot paths alone to compare apples to apples we'd want something more
fine grained.

  Luis