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

[Keith Busch <kbusch@kernel.org>]

On Thu, Nov 13, 2025 at 08:02:37PM +0000, Eric Biggers wrote:
> On Thu, Nov 13, 2025 at 02:48:43PM -0500, Keith Busch wrote:
> > Like on real hardware? I'm a bit at a loss as to how, I've never seen
> > anything subscribe to this format, not even in emulation. The only thing
> > I can readily do to test this is run random data through the old code,
> > print the result, then run the same data through the new code and see if
> > they're the same. That test is successful. Not good enough?
> 
> ip_compute_csum() returns a folded 16-bit checksum, whereas
> csum_partial() returns an unfolded 32-bit checksum.

Sorry, I must be missing something. do_csum() returns an unfolded 32-bit
result, and it is just getting down cast to a 16-bit result. Where does
the folding happen?

__sum16 ip_compute_csum(const void *buff, int len)
{
        return (__force __sum16)~do_csum(buff, len);
}

In any case, I find that running any random data through it at block
interval lengths (4k or 512b) is always producing results that fit in 16
bits anyway, so maybe that's why it appears to be working?

> I don't see how the
> checksums can be the same as before.  Hence my concern about whether
> this was tested.  It could be with hardware, an emulator, or a unit
> test.

Martin pointed to a good in-kernel debug module that can do it.  I'll
set a test up with that.