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Date: Mon, 5 Oct 2026 15:11:26 +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 16/21] xfs: add data checksum support to zoned garbage
 collection
Message-ID: <20261005131126.GD26805@lst.de>
References: <20260924100032.2733101-1-hch@lst.de> <20260924100032.2733101-17-hch@lst.de> <20260929010639.GX2705364@frogsfrogsfrogs>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Sep 28, 2026 at 06:06:39PM -0700, Darrick J. Wong wrote:
> > +	/* Buffer for data checksums */
> > +	struct xfs_buf			*csum_bp;
> > +	void				*csum_buf;
> 
> Where is csum_buf used?

Nowhere, left from an earlier version.

> > +		error = xfs_rtcsum_read_async(mp, chunk->old_startblock,
> > +				&chunk->csum_bp);
> > +		if (error) {
> > +			xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
> > +			xfs_zone_gc_free_chunk(chunk);
> > +			return false;
> > +		}
> 
> Ok so this starts the csum block read asynchronously, and then submits
> the read bio.  chunk->csum_bp is the checksum buffer of the rtcsum file
> of the zone we're cleaning out, right?

Yes.

> > +		boff = xfs_rtb_to_rtcsumoff(mp, chunk->old_startblock);
> > +		error = xfs_rtcsum_log(chunk->oz, chunk->new_daddr, chunk->len,
> > +				chunk->csum_bp->b_addr + boff);
> 
> ...and then write the same checksum to the new daddr using the old
> checksum.  There's no explicit validation of the checksum in the garbage
> collector itself, but I gather the read ioend did this for us already,
> right?

Exactly.