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

[Christoph Hellwig]

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?