linux-kernel - Re: [PATCH v7 0/6] block: Introduce REQ_ALLOCATE flag for REQ_OP_WRITE

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Date:   Thu, 26 Mar 2020 02:29:35 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, axboe@...nel.dk,
        bob.liu@...cle.com, agk@...hat.com, snitzer@...hat.com,
        dm-devel@...hat.com, song@...nel.org, tytso@....edu,
        adilger.kernel@...ger.ca, Chaitanya.Kulkarni@....com,
        ming.lei@...hat.com, osandov@...com, jthumshirn@...e.de,
        minwoo.im.dev@...il.com, damien.lemoal@....com,
        andrea.parri@...rulasolutions.com, hare@...e.com, tj@...nel.org,
        ajay.joshi@....com, sagi@...mberg.me, dsterba@...e.com,
        bvanassche@....org, dhowells@...hat.com, asml.silence@...il.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 0/6] block: Introduce REQ_ALLOCATE flag for
 REQ_OP_WRITE_ZEROES

On Wed, Mar 25, 2020 at 01:23:33PM -0400, Martin K. Petersen wrote:
> 
> Christoph,
> 
> > I am very much against that for the following reason:
> >
> >  - the current REQ_OP_DISCARD is purely a hint, and implementations can
> >    (and do) choose to ignore it
> >
> >  - REQ_OP_WRITE_ZEROES is an actual data integrity operation with
> >    everything that entails
> 
> If you want to keep emphasis on the "integrity operation" instead of the
> provisioning aspect, would you expect REQ_ALLOCATE (which may or may not
> zero blocks) to be considered a deterministic operation or a
> non-deterministic one? Should this depend on whether the device
> guarantees zeroing when provisioning blocks or not?

That's why I don't like the whole flags game very much.  I'd rather
have REQ_OP_WRITE_ZEROES as the integrity operation that gurantees
zeroing, and a REQ_ALLOCATE that doesn't guarantee zeroing, just some
deterministic state of the blocks.