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Date: Tue, 15 Jul 2025 13:29:52 +0200
From: Christoph Hellwig <hch@lst.de>
To: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, John Garry <john.g.garry@oracle.com>,
	Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-block@vger.kernel.org, linux-nvme@lists.infradead.org
Subject: Re: Do we need an opt-in for file systems use of hw atomic writes?
Message-ID: <20250715112952.GA23935@lst.de>
References: <20250714131713.GA8742@lst.de> <6c3e1c90-1d3d-4567-a392-85870226144f@oracle.com> <aHULEGt3d0niAz2e@infradead.org> <6babdebb-45d1-4f33-b8b5-6b1c4e381e35@oracle.com> <20250715060247.GC18349@lst.de> <20250715-rundreise-resignieren-34550a8d92e3@brauner>
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On Tue, Jul 15, 2025 at 12:02:06PM +0200, Christian Brauner wrote:
> > I'm not sure a XFLAG is all that useful.  It's not really a per-file
> > persistent thing.  It's more of a mount option, or better persistent
> > mount-option attr like we did for autofsck.
> 
> If we were to make this a mount option it would be really really ugly.
> Either it is a filesystem specific mount option and then we have the
> problem that we're ending up with different mount option names
> per-filesystem.

Not that I'm arguing for a mount option (this should be sticky), but
we've had plenty of fs parsed mount options with common semantics.

> It feels like this is something that needs to be done on the block
> layer. IOW, maybe add generic block layer ioctls or a per-device sysfs
> entry that allows to turn atomic writes on or off. That information
> would then also potentially available to the filesystem to e.g.,
> generate an info message during mount that hardware atomics are used or
> aren't used. Because ultimately the block layer is where the decision
> needs to be made.

The block layer just passes things through.