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Date: Thu, 15 Jan 2026 07:17:27 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Christian Brauner <brauner@kernel.org>,
	Carlos Maiolino <cem@kernel.org>, Qu Wenruo <wqu@suse.com>,
	Al Viro <viro@zeniv.linux.org.uk>, linux-block@vger.kernel.org,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 06/14] iomap: fix submission side handling of
 completion side errors
Message-ID: <20260115061727.GD9205@lst.de>
References: <20260114074145.3396036-1-hch@lst.de> <20260114074145.3396036-7-hch@lst.de> <20260114223558.GK15551@frogsfrogsfrogs>
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On Wed, Jan 14, 2026 at 02:35:58PM -0800, Darrick J. Wong wrote:
> On Wed, Jan 14, 2026 at 08:41:04AM +0100, Christoph Hellwig wrote:
> > The "if (dio->error)" in iomap_dio_bio_iter exists to stop submitting
> > more bios when a completion already return an error.  Commit cfe057f7db1f
> > ("iomap_dio_actor(): fix iov_iter bugs") made it revert the iov by
> > "copied", which is very wrong given that we've already consumed that
> > range and submitted a bio for it.
> 
> Is it possible for the error to be ENOTBLK and the caller wants to fall
> back to buffered IO?  I /think/ the answer is "no" because only the
> ->iomap_begin methods (and therefore iomap_iter()) should be doing that,
> and we mask the ENOTBLK and pretend it's a short write.  Right?

Yeah, returning that on completion is too late to fall back, because
the iov_iter is already consumed.