Commit b1a000d3 authored by Keith Busch's avatar Keith Busch Committed by Jens Axboe
Browse files

block: relax direct io memory alignment 



Use the address alignment requirements from the block_device for direct
io instead of requiring addresses be aligned to the block size. User
space can discover the alignment requirements from the dma_alignment
queue attribute.

User space can specify any hardware compatible DMA offset for each
segment, but every segment length is still required to be a multiple of
the block size.

Signed-off-by: default avatarKeith Busch <kbusch@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220610195830.3574005-11-kbusch@fb.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 5debd969

block/bio.c

+9 −0
Original line number Diff line number Diff line
@@ -1220,7 +1220,16 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) 
	BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);

	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);



	/*

	 * Each segment in the iov is required to be a block size multiple.

	 * However, we may not be able to get the entire segment if it spans

	 * more pages than bi_max_vecs allows, so we have to ALIGN_DOWN the

	 * result to ensure the bio's total size is correct. The remainder of

	 * the iov data will be picked up in the next bio iteration.

	 */

	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);

	if (size > 0)

		size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev));

	if (unlikely(size <= 0))

		return size ? size : -EFAULT;

block/fops.c

+2 −2
Original line number Diff line number Diff line
@@ -45,8 +45,8 @@ static unsigned int dio_bio_write_op(struct kiocb *iocb) 
static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,

			      struct iov_iter *iter)

{

	return ((pos | iov_iter_alignment(iter)) &

	    (bdev_logical_block_size(bdev) - 1));

	return pos & (bdev_logical_block_size(bdev) - 1) ||

		!bdev_iter_is_aligned(bdev, iter);

}



#define DIO_INLINE_BIO_VECS 4

include/linux/blkdev.h

+5 −0
Original line number Diff line number Diff line
@@ -424,6 +424,11 @@ struct request_queue { 
	unsigned long		nr_requests;	/* Max # of requests */



	unsigned int		dma_pad_mask;

	/*

	 * Drivers that set dma_alignment to less than 511 must be prepared to

	 * handle individual bvec's that are not a multiple of a SECTOR_SIZE

	 * due to possible offsets.

	 */

	unsigned int		dma_alignment;



#ifdef CONFIG_BLK_INLINE_ENCRYPTION