Commit afdc1a78 authored Apr 11, 2008 by FUJITA Tomonori Committed by Jens Axboe Apr 21, 2008

block: add bio_copy_user_iov support to blk_rq_map_user_iov



With this patch, blk_rq_map_user_iov uses bio_copy_user_iov when a low
level driver needs padding or a buffer in sg_iovec isn't aligned. That
is, it uses temporary kernel buffers instead of mapping user pages
directly.

When a LLD needs padding, later blk_rq_map_sg needs to extend the last
entry of a scatter list. bio_copy_user_iov guarantees that there is
enough space for padding by using temporary kernel buffers instead of
user pages.

blk_rq_map_user_iov needs buffers in sg_iovec to be aligned. The
comment in blk_rq_map_user_iov indicates that drivers/scsi/sg.c also
needs buffers in sg_iovec to be aligned. Actually, drivers/scsi/sg.c
works with unaligned buffers in sg_iovec (it always uses temporary
kernel buffers).

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

parent c5dec1c3

block/blk-map.c

+17 −5

Original line number	Diff line number	Diff line
		@@ -5,6 +5,7 @@
		#include <linux/module.h>
		#include <linux/bio.h>
		#include <linux/blkdev.h>
		#include <scsi/sg.h> /* for struct sg_iovec */

		#include "blk.h"

		@@ -194,15 +195,26 @@ int blk_rq_map_user_iov(struct request_queue q, struct request rq,
		struct sg_iovec *iov, int iov_count, unsigned int len)
		{
		struct bio *bio;
		int i, read = rq_data_dir(rq) == READ;
		int unaligned = 0;

		if (!iov \|\| iov_count <= 0)
		return -EINVAL;

		/* we don't allow misaligned data like bio_map_user() does. If the
		* user is using sg, they're expected to know the alignment constraints
		* and respect them accordingly */
		bio = bio_map_user_iov(q, NULL, iov, iov_count,
		rq_data_dir(rq) == READ);
		for (i = 0; i < iov_count; i++) {
		unsigned long uaddr = (unsigned long)iov[i].iov_base;

		if (uaddr & queue_dma_alignment(q)) {
		unaligned = 1;
		break;
		}
		}

		if (unaligned \|\| (q->dma_pad_mask & len))
		bio = bio_copy_user_iov(q, iov, iov_count, read);
		else
		bio = bio_map_user_iov(q, NULL, iov, iov_count, read);

		if (IS_ERR(bio))
		return PTR_ERR(bio);