linux-kernel - Re: [PATCHv2 1/7] block: check for valid bio while splitting

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Message-ID: <aJjThNwGsrjFtWlg@infradead.org>
Date: Sun, 10 Aug 2025 10:14:44 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Keith Busch <kbusch@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>, Keith Busch <kbusch@...a.com>,
	linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, snitzer@...nel.org, axboe@...nel.dk,
	dw@...idwei.uk, brauner@...nel.org, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCHv2 1/7] block: check for valid bio while splitting

On Sun, Aug 10, 2025 at 09:39:50AM -0600, Keith Busch wrote:
> > >  	bytes = ALIGN_DOWN(bytes, bio_split_alignment(bio, lim));
> > > +	if (!bytes)
> > > +		return -EINVAL;
> > 
> > How is this related to the other hunk and the patch description?
> 
> The patchset allows you to submit an io with vectors that are partial
> logical blocks. Misuse could create a bio that exceeds the device max
> vectors or introduces virtual boundary gaps, requiring a split into
> something that is smaller than a block size. This check catches that.
> 
> Quick example: nvme with a 4k logical block size, and the usual 4k
> virtual boundary. Send an io with four vectors iov_len=1k. The total
> size is block sized, but there's no way that could split into a valid
> io. There's a test specifically for this in my reply about xfstests.

Can you turn the above into a comment explaining the check?