linux-kernel - Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

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Message-ID: <20231109151531.GC32432@lst.de>
Date:   Thu, 9 Nov 2023 16:15:31 +0100
From:   Christoph Hellwig <hch@....de>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Bart Van Assche <bvanassche@....org>,
        John Garry <john.g.garry@...cle.com>,
        Eric Biggers <ebiggers@...nel.org>, 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,
        Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

On Mon, Oct 02, 2023 at 08:28:04PM -0400, Martin K. Petersen wrote:
> 
> Bart,
> 
> > Neither the SCSI SBC standard nor the NVMe standard defines a "minimum
> > atomic write unit". So why to introduce something in the Linux kernel
> > that is not defined in common storage standards?
> 
> >From SBC-5:
> 
> "The ATOMIC TRANSFER LENGTH GRANULARITY field indicates the minimum
> transfer length for an atomic write command."

I would suggest that we don't try to claim any atomic write capability
if this is not a logical block as such devices are completely useless.
In fact I'd add a big warning to the kernel log if a device claims this,
as this breaks all the implicit assumptions that a single logical
block write is atomic.