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

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Message-ID: <a2077ddf-9a8f-4101-aeb9-605d6dee3c6e@acm.org>
Date:   Thu, 5 Oct 2023 10:10:45 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     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 10/4/23 11:17, Martin K. Petersen wrote:
> 
> Hi Bart!
> 
>> In other words, also for the above example it is guaranteed that 
>> writes of a single logical block (512 bytes) are atomic, no matter
>> what value is reported as the ATOMIC TRANSFER LENGTH GRANULARITY.
> 
> There is no formal guarantee that a disk drive sector 
> read-modify-write operation results in a readable sector after a 
> power failure. We have definitely seen blocks being mangled in the 
> field.

Aren't block devices expected to use a capacitor that provides enough
power to handle power failures cleanly?

How about blacklisting block devices that mangle blocks if a power
failure occurs? I think such block devices are not compatible with
journaling filesystems nor with log-structured filesystems.

Thanks,

Bart.