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Date: Tue, 15 Jul 2025 08:02:47 +0200
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>, Christoph Hellwig <hch@lst.de>,
	"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: <20250715060247.GC18349@lst.de>
References: <20250714131713.GA8742@lst.de> <6c3e1c90-1d3d-4567-a392-85870226144f@oracle.com> <aHULEGt3d0niAz2e@infradead.org> <6babdebb-45d1-4f33-b8b5-6b1c4e381e35@oracle.com>
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On Mon, Jul 14, 2025 at 04:53:49PM +0100, John Garry wrote:
> I see. I figure that something like a FS_XFLAG could be used for that. But 
> we should still protect bdev fops users as well.

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.

>
> JFYI, I have done a good bit of HW and SW-based atomic powerfail testing 
> with fio on a Linux dev board, so there is a decent method available for 
> users to verify their HW atomics. But then testing power failures is not 
> always practical. Crashing the kernel only tests AWUN, and AWUPF (for 
> NVMe).

Yes.  There's some ways to emulate power fail for file system level
power fail testing using dm-log-writes and similar, but that doesn't
help at all with testing the power fail behavior of the device which
we rely on here.