linux-kernel - Re: [PATCH 10/21] block: Add fops atomic write support

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Message-ID: <2bb2a4d0-4f1f-45f1-9196-f5d0d8ee1878@acm.org>
Date:   Fri, 6 Oct 2023 10:22:08 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Dave Chinner <david@...morbit.com>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        John Garry <john.g.garry@...cle.com>, axboe@...nel.dk,
        kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, djwong@...nel.org, viro@...iv.linux.org.uk,
        brauner@...nel.org, chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org
Subject: Re: [PATCH 10/21] block: Add fops atomic write support

On 10/5/23 21:31, Dave Chinner wrote:
> Then I don't see what your concern is.
> 
> Single sector writes are guaranteed atomic and have been for as long 
> as I've worked in this game. OTOH, multi-sector writes are not 
> guaranteed to be atomic - they can get torn on sector boundaries, but
> the individual sectors within that write are guaranteed to be 
> all-or-nothing.
> 
> Any hardware device that does not guarantee single sector write 
> atomicity (i.e. tears in the middle of a sector) is, by definition, 
> broken. And we all know that broken hardware means nothing in the 
> storage stack works as it should, so I just don't see what point you 
> are trying to make...

Do you agree that the above implies that it is not useful in patch 01/21
of this series to track atomic_write_unit_min_bytes in the block layer
nor to export this information to user space? The above implies that
this parameter will always be equal to the logical block size. Writes to
a single physical block happen atomically. If there are multiple logical
blocks per physical block, the block device must serialize 
read/modify/write cycles internally.

Thanks,

Bart.