Re: [PATCHv4] blk-integrity: support arbitrary buffer alignment

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Nov 13, 2025 at 01:14:13PM -0500, Keith Busch wrote:
> On Thu, Nov 13, 2025 at 09:31:35AM -0800, Eric Biggers wrote:
> > On Thu, Nov 13, 2025 at 07:26:21AM -0800, Keith Busch wrote:
> > > +static void blk_set_ip_pi(struct t10_pi_tuple *pi,
> > > +			  struct blk_integrity_iter *iter)
> > >  {
> > > -	u8 offset = bi->pi_offset;
> > > -	unsigned int i;
> > > -
> > > -	for (i = 0 ; i < iter->data_size ; i += iter->interval) {
> > > -		struct crc64_pi_tuple *pi = iter->prot_buf + offset;
> > > +	__be16 csum = (__force __be16)~(lower_16_bits(iter->crc));
> > 
> > This just throws away half of the checksum instead of properly combining
> > the two halves.  How is this being tested?
> 
> Yeah, this is the only guard type I've never seen a device subscribe to,
> so not particularly easily tested on my side. I just forced the code
> path down here anyway and checked if the result matches the result from
> the existing code calling "ip_compute_csum()". Maybe I can just continue
> using that as I suspect devices using that can't handle split data
> intervals that I'm trying to enable.

Wouldn't csum_fold() combine the halves correctly?

Anyway, it needs to be tested.

- Eric