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

[Christoph Hellwig <hch@lst.de>]

On Sat, Nov 08, 2025 at 09:20:08AM -0700, Keith Busch wrote:
> > 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.

I guess we'll just need a flag to distinguish the SCSI vs NVMe
(or HBA vs integrated) semantics here.