Re: block/t10-pi.c: blk_integrity_interval() prot_iter misalignment with extended metadata

[Christoph Hellwig <hch@infradead.org>]

On Wed, Aug 12, 2026 at 02:37:28PM +0200, Ricardo AlgRicSpain wrote:
> Hi,
> 
> blk_integrity_interval() (block/t10-pi.c:270-305) advances prot_iter
> inconsistently:
> 
> - fast path (t10-pi.c:282): advances metadata_size - pi_offset bytes
> - split-tuple path (t10-pi.c:285-287, 296-299): advances only
>   pi_tuple_size bytes via blk_integrity_copy_to_tuple/copy_from_tuple
> 
> When metadata_size - pi_offset > pi_tuple_size (e.g. NVMe extended
> metadata) and the tuple splits across bvec segments, prot_iter
> under-advances by the trailing opaque bytes, and the offset accumulates
> across subsequent intervals, breaking guard/data correspondence on
> verify and generate.
> 
> Suggested fix: after copy_to_tuple/copy_from_tuple, advance the
> remaining bytes:
> 
>     bvec_iter_advance(iter->bip->bip_vec, &iter->prot_iter,
>             iter->bi->metadata_size - iter->bi->pi_offset -
>             iter->bi->pi_tuple_size);
> 
> ...matching what blk_tuple_remap_end() already does (t10-pi.c:426-436).
> 
> Standalone C PoC reproducing the misalignment attached (poc.c).

Please send a patch with your proposed fix.  Wiring up your reproducer
in blktests would also be very helpful.