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Date: Tue, 9 Jan 2024 17:02:23 +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,
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Subject: Re: [PATCH v2 00/16] block atomic writes
Message-ID: <20240109160223.GA7737@lst.de>
References: <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> <20231219151759.GA4468@lst.de> <fff50006-ccd2-4944-ba32-84cbb2dbd1f4@oracle.com> <20231221065031.GA25778@lst.de> <73d03703-6c57-424a-80ea-965e636c34d6@oracle.com>
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On Tue, Jan 09, 2024 at 09:55:24AM +0000, John Garry wrote:
> So a user can issue:
>
> >xfs_io -c "atomic-writes 64K" mnt/file
> >xfs_io -c "atomic-writes" mnt/file
> [65536] mnt/file

Let me try to decipher that:

 - the first call sets a 64k fsx_atomicwrites_size size
 - the secon call queries fsx_atomicwrites_size?

> The user will still have to issue statx to get the actual atomic write 
> limit for a file, as 'xfs_io -c "atomic-writes"' does not take into account 
> any HW/linux block layer atomic write limits.

So will the set side never fail?

> Is this the sort of userspace API which you would like to see?

What I had in mind (and that's doesn't mean it's right..) was that
the user just sets a binary flag, and the fs reports the best it
could.  But there might be reasons to do it differently.