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Date: Fri, 13 Dec 2024 15:47:40 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>, brauner@kernel.org,
	cem@kernel.org, dchinner@redhat.com, hch@lst.de,
	ritesh.list@gmail.com, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	martin.petersen@oracle.com
Subject: Re: [PATCH v2 2/7] iomap: Add zero unwritten mappings dio support
Message-ID: <20241213144740.GA17593@lst.de>
References: <20241210125737.786928-1-john.g.garry@oracle.com> <20241210125737.786928-3-john.g.garry@oracle.com> <20241211234748.GB6678@frogsfrogsfrogs> <4d34e14f-6596-483b-86e8-d4b7e44acd9a@oracle.com> <20241212204007.GL6678@frogsfrogsfrogs>
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On Thu, Dec 12, 2024 at 12:40:07PM -0800, Darrick J. Wong wrote:
> > However, I still think that we should be able to atomic write mixed extents,
> > even though it is a pain to implement. To that end, I could be convinced
> > again that we don't require it...
> 
> Well... if you /did/ add a few entries to include/uapi/linux/fs.h for
> ways that an untorn write can fail, then we could define the programming
> interface as so:
> 
> "If you receive -EBADMAP, then call fallocate(FALLOC_FL_MAKE_OVERWRITE)
> to force all the mappings to pure overwrites."

Ewwwwwwwwwwwwwwwwwwwww.

That's not a sane API in any way.

> ...since there have been a few people who have asked about that ability
> so that they can write+fdatasync without so much overhead from file
> metadata updates.

And all of them fundamentally misunderstood file system semantics and/or
used weird bypasses that are dommed to corrupt the file system sooner
or later.