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Date: Thu, 9 Nov 2023 16:15:31 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
	John Garry <john.g.garry@oracle.com>,
	Eric Biggers <ebiggers@kernel.org>, axboe@kernel.dk,
	kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, jejb@linux.ibm.com,
	djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org,
	chandan.babu@oracle.com, dchinner@redhat.com,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
	linux-api@vger.kernel.org,
	Prasad Singamsetty <prasad.singamsetty@oracle.com>
Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx
Message-ID: <20231109151531.GC32432@lst.de>
References: <20230929102726.2985188-1-john.g.garry@oracle.com> <20230929102726.2985188-4-john.g.garry@oracle.com> <20230929224922.GB11839@google.com> <b9c266d2-d5d6-4294-9a95-764641e295b4@acm.org> <d3a8b9b0-b24c-a002-e77d-56380ee785a5@oracle.com> <2c929105-7c7f-43c5-a105-42d1813d0e29@acm.org> <yq1r0mctv2d.fsf@ca-mkp.ca.oracle.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

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.