[PATCH] block: only fail dma-buf bios that need block layer PI

[Christoph Hellwig]

On Wed, Oct 28, 2026 at 06:14:12PM +0000, Kyle Bader wrote:
> From: Kyle Bader <kbader at ibm.com>
> 
> Any dma-buf I/O to a device with a PI checksum fails today.
> blkdev_init_dma_buf_io_ctx() returns -EOPNOTSUPP at registration, and
> blk_mq_submit_bio() fails each dma-buf bio with BLK_STS_NOTSUPP. The
> checks prevent a crash: bi_dmabuf_map shares a union with bi_io_vec,
> and bio_integrity_generate() and bio_integrity_verify() walk bi_io_vec
> to compute the guards over the data.

Please cut down the commit log to the essentials.  It's basicallyr
currently all P2P I/O to devices advertizing integrity data is rejected,
but it should only reject those walking the bio_vecs.