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Date: Mon, 5 Oct 2026 14:59:27 +0200
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Carlos Maiolino <cem@kernel.org>,
	Jens Axboe <axboe@kernel.dk>,
	Christian Brauner <brauner@kernel.org>, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 14/21] xfs: add support for reading with data checksums
Message-ID: <20261005125927.GA26805@lst.de>
References: <20260924100032.2733101-1-hch@lst.de> <20260924100032.2733101-15-hch@lst.de> <20260929004204.GV2705364@frogsfrogsfrogs>
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On Mon, Sep 28, 2026 at 05:42:04PM -0700, Darrick J. Wong wrote:
> > +	error = -EIO;
> > +	if (WARN_ON_ONCE(ioend->io_bio.bi_iter.bi_idx))
> 
> What does this warning mean?  That we've somehow already advanced the
> bvec iterator?

Yes.  I've added the following comment:

	/*
         * The main I/O end bio is either freshly build by iomap, and has both
         * bi_idx and bi_offset set to zero, or comes from a bvec iter for
         * direct I/O, in which case bi_offset can be non-zero, but bi_idx still
         * must be zero as the bio always points to the first actually used
         * bio_vec in the iov_iter.
         */


> > +	/* No bp for early xfs_rtcsum_prepare_read failures. */
> > +	if (!bp)
> > +		return error;
> 
> Is it possible for error to be zero here?

It shouldn't.  I've added an assert and clarified the comment.