linux-kernel - Re: [PATCH v2 00/16] block atomic writes

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Date: Tue, 9 Jan 2024 17:02:23 +0100
From: Christoph Hellwig <hch@....de>
To: John Garry <john.g.garry@...cle.com>
Cc: Christoph Hellwig <hch@....de>, "Darrick J. Wong" <djwong@...nel.org>,
	axboe@...nel.dk, kbusch@...nel.org, sagi@...mberg.me,
	jejb@...ux.ibm.com, martin.petersen@...cle.com,
	viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com,
	jack@...e.cz, 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-scsi@...r.kernel.org,
	ming.lei@...hat.com, bvanassche@....org, ojaswin@...ux.ibm.com
Subject: Re: [PATCH v2 00/16] block atomic writes

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.