Re: [PATCHv3] blk-integrity: support arbitrary buffer alignment

[Keith Busch <kbusch@kernel.org>]

On Fri, Nov 07, 2025 at 10:52:14PM -0500, Martin K. Petersen wrote:
> > +static void blk_crc(struct blk_integrity_iter *iter, void *data,
> > +		    unsigned int len)
> 
> Maybe blk_calculate_checksum() or blk_calculate_guard()? It's a bit
> weird to refer to the IP checksum as a CRC.

Sounds good.
 
> To my knowledge, no SCSI controller can handle PI split across segments
> and the PI tuples are required to be naturally aligned in memory. SCSI
> controllers probably can't handle split data segments either since the
> design constraint is one PI segment per protection interval sized data
> segment.

There are not many nvme controllers that can handle split pi segments
either. Anything setting ID_CTRL SGLS.MSDS can do it, but it's a rarely
advertised capability. For everyone else, metadata buffers have a single
segment limit.

As for interval data split across segments, that's totally fine for any
nvme that supports PI formats. That kind of data was mainly what I was
initially trying to handle here since that's sufficient to reinstate the
lower dma_alignment limit. It wasn't much more work to support split pi
though, unlikely as it is to have hardware capable of it.