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Date: Tue, 19 Dec 2023 16:17:59 +0100
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>, "Darrick J. Wong" <djwong@kernel.org>,
	axboe@kernel.dk, kbusch@kernel.org, sagi@grimberg.me,
	jejb@linux.ibm.com, martin.petersen@oracle.com,
	viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com,
	jack@suse.cz, 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-scsi@vger.kernel.org,
	ming.lei@redhat.com, jaswin@linux.ibm.com, bvanassche@acm.org
Subject: Re: [PATCH v2 00/16] block atomic writes
Message-ID: <20231219151759.GA4468@lst.de>
References: <20231212110844.19698-1-john.g.garry@oracle.com> <20231212163246.GA24594@lst.de> <b8b0a9d7-88d2-45a9-877a-ecc5e0f1e645@oracle.com> <20231213154409.GA7724@lst.de> <c729b03c-b1d1-4458-9983-113f8cd752cd@oracle.com> <20231219051456.GB3964019@frogsfrogsfrogs> <20231219052121.GA338@lst.de> <76c85021-dd9e-49e3-80e3-25a17c7ca455@oracle.com>
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On Tue, Dec 19, 2023 at 12:41:37PM +0000, John Garry wrote:
> How about something based on fcntl, like below? We will prob also require 
> some per-FS flag for enabling atomic writes without HW support. That flag 
> might be also useful for XFS for differentiating forcealign for atomic 
> writes with just forcealign.

I would have just exposed it through a user visible flag instead of
adding yet another ioctl/fcntl opcode and yet another method.

And yes, for anything that doesn't always support atomic writes it would
need to be persisted.