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Date: Sat, 26 Sep 2026 08:15:02 +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 13/21] xfs: require file system block size alignment
 when using data checksums
Message-ID: <20260926061502.GF20636@lst.de>
References: <20260924100032.2733101-1-hch@lst.de> <20260924100032.2733101-14-hch@lst.de> <20260925232456.GH2705364@frogsfrogsfrogs>
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On Fri, Sep 25, 2026 at 04:24:56PM -0700, Darrick J. Wong wrote:
> > +	/*
> > +	 * Each checksums covers a whole file system block, and thus sub-fsblock
> > +	 * reads are not supported for file systems using data checksums.
> > +	 */
> > +	if (xfs_is_rtcsum_inode(ip))
> > +		stat->dio_read_offset_align = xfs_inode_alloc_unitsize(ip);
> 
> The allocation unit could be larger than the fsblock size, why is it
> necessary to have such large directio reads on a checksummed file?
> Though come to think of it zoned mode doesn't allow rtextsize > 1fsb
> so this question might be hair-splitting.

Exactly, allocsize is always the blocksize here.

> 
> I think you could reuse xfs_read_bounce_minsize() here.

Not a bad idea.  Let's see if our header mess allows doing that as an
inline, as doing function call for it would be a bit silly.