Re: [PATCH 16/17] blk-map/bio: remove superflous @len parameter fromblk_rq_map_user_iov()

From: Boaz Harrosh
Date: Wed Apr 01 2009 - 13:14:44 EST

On 04/01/2009 04:44 PM, Tejun Heo wrote:
> Impact: API cleanup
>
> blk_rq_map_user_iov() took @len parameter which contains duplicate
> information as the total length is available as the sum of all iov
> segments. This doesn't save anything either as the mapping function
> should walk the whole iov on entry to check for alignment anyway.
> Remove the superflous parameter.
>
> Removing the superflous parameter removes the pathological corner case
> where the caller passes in shorter @len than @iov but @iov mappings
> ends up capped due to queue limits and bio->bi_size ends up matching
> @len thus resulting in successful map.

I did not go to the bottom of this but how does that do not change user-space
API. It would now fail in code that would work before.

What if I want to try variable size commands, where I try the shorter
first, then a longer one (or vis versa). I would setup memory mapping to the biggest
command but issue a length that correspond to the encoded command inside the CDB.

The bi->bi_size is not only mapping size it is also the command size I want to
actually read/write.

But I might read this wrong though

> With the superflous parameter
> gone, blk-map/bio can now simply fail partial mappings.
>
> Move partial mapping detection to bio_create_from_sgl() which is
> shared by all map/copy paths and remove partial mapping handling from
> all other places.
>
> This change removes one of the two users of __blk_rq_unmap_user() and
> it gets collapsed into blk_rq_unmap_user().
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> ---
> block/blk-map.c | 47 +++++++++++++++--------------------------------
> block/scsi_ioctl.c | 11 +++--------
> drivers/scsi/sg.c | 2 +-
> fs/bio.c | 43 +++++++++++++++++--------------------------
> include/linux/blkdev.h | 2 +-
> 5 files changed, 37 insertions(+), 68 deletions(-)
>
> diff --git a/block/blk-map.c b/block/blk-map.c
> index dc4097c..f60f439 100644
> --- a/block/blk-map.c
> +++ b/block/blk-map.c
> @@ -8,20 +8,6 @@
>
> #include "blk.h"
>
> -static int __blk_rq_unmap_user(struct bio *bio)
> -{
> - int ret = 0;
> -
> - if (bio) {
> - if (bio_flagged(bio, BIO_USER_MAPPED))
> - bio_unmap_user(bio);
> - else
> - ret = bio_uncopy_user(bio);
> - }
> -
> - return ret;
> -}
> -
> /**
> * blk_rq_map_user_iov - map user data to a request, for REQ_TYPE_BLOCK_PC usage
> * @q: request queue where request should be inserted
> @@ -29,7 +15,6 @@ static int __blk_rq_unmap_user(struct bio *bio)
> * @md: pointer to the rq_map_data holding pages (if necessary)
> * @iov: pointer to the iovec
> * @count: number of elements in the iovec
> - * @len: I/O byte count
> * @gfp: memory allocation flags
> *
> * Description:
> @@ -47,7 +32,7 @@ static int __blk_rq_unmap_user(struct bio *bio)
> */
> int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
> struct rq_map_data *md, struct iovec *iov, int count,
> - unsigned int len, gfp_t gfp)
> + gfp_t gfp)
> {
> struct bio *bio = ERR_PTR(-EINVAL);
> int rw = rq_data_dir(rq);
> @@ -62,23 +47,17 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
> if (IS_ERR(bio))
> return PTR_ERR(bio);
>
> - if (bio->bi_size != len) {
> - /*
> - * Grab an extra reference to this bio, as bio_unmap_user()
> - * expects to be able to drop it twice as it happens on the
> - * normal IO completion path
> - */
> - bio_get(bio);
> - bio_endio(bio, 0);
> - __blk_rq_unmap_user(bio);
> - return -EINVAL;
> - }
> -
> if (!bio_flagged(bio, BIO_USER_MAPPED))
> rq->cmd_flags |= REQ_COPY_USER;
>
> - blk_queue_bounce(q, &bio);
> + /*
> + * Grab an extra reference to this bio, as bio_unmap_user()
> + * expects to be able to drop it twice as it happens on the
> + * normal IO completion path.
> + */
> bio_get(bio);
> +
> + blk_queue_bounce(q, &bio);
> blk_rq_bio_prep(q, rq, bio);
> rq->buffer = rq->data = NULL;
> return 0;
> @@ -116,7 +95,7 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
> iov.iov_base = ubuf;
> iov.iov_len = len;
>
> - return blk_rq_map_user_iov(q, rq, md, &iov, 1, len, gfp);
> + return blk_rq_map_user_iov(q, rq, md, &iov, 1, gfp);
> }
> EXPORT_SYMBOL(blk_rq_map_user);
>
> @@ -132,12 +111,16 @@ EXPORT_SYMBOL(blk_rq_map_user);
> int blk_rq_unmap_user(struct bio *bio)
> {
> struct bio *mapped_bio = bio;
> - int ret;
> + int ret = 0;
>
> if (unlikely(bio_flagged(bio, BIO_BOUNCED)))
> mapped_bio = bio->bi_private;
>
> - ret = __blk_rq_unmap_user(mapped_bio);
> + if (bio_flagged(bio, BIO_USER_MAPPED))
> + bio_unmap_user(mapped_bio);
> + else
> + ret = bio_uncopy_user(mapped_bio);
> +
> bio_put(bio);
> return ret;
> }
> diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
> index 73cfd91..fd538f8 100644
> --- a/block/scsi_ioctl.c
> +++ b/block/scsi_ioctl.c
> @@ -288,7 +288,6 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
>
> if (hdr->iovec_count) {
> const int size = sizeof(struct sg_iovec) * hdr->iovec_count;
> - size_t iov_data_len;
> struct iovec *iov;
>
> iov = kmalloc(size, GFP_KERNEL);
> @@ -304,15 +303,11 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
> }
>
> /* SG_IO howto says that the shorter of the two wins */
> - iov_data_len = iov_length(iov, hdr->iovec_count);
> - if (hdr->dxfer_len < iov_data_len) {
> - hdr->iovec_count = iov_shorten(iov, hdr->iovec_count,
> - hdr->dxfer_len);
> - iov_data_len = hdr->dxfer_len;
> - }
> + hdr->iovec_count = iov_shorten(iov, hdr->iovec_count,
> + hdr->dxfer_len);
>
> ret = blk_rq_map_user_iov(q, rq, NULL, iov, hdr->iovec_count,
> - iov_data_len, GFP_KERNEL);
> + GFP_KERNEL);
> kfree(iov);
> } else if (hdr->dxfer_len)
> ret = blk_rq_map_user(q, rq, NULL, hdr->dxferp, hdr->dxfer_len,
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index b4ef2f8..5fcf436 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1673,7 +1673,7 @@ static int sg_start_req(Sg_request *srp, unsigned char *cmd)
>
> if (iov_count)
> res = blk_rq_map_user_iov(q, rq, md, hp->dxferp, iov_count,
> - hp->dxfer_len, GFP_ATOMIC);
> + GFP_ATOMIC);
> else
> res = blk_rq_map_user(q, rq, md, hp->dxferp,
> hp->dxfer_len, GFP_ATOMIC);
> diff --git a/fs/bio.c b/fs/bio.c
> index fe796dc..9466b05 100644
> --- a/fs/bio.c
> +++ b/fs/bio.c
> @@ -956,14 +956,14 @@ static void bio_memcpy_sgl_sgl(struct scatterlist *dsgl, int dnents,
> * @nr_pages: number of pages in @sgl
> * @rw: the data direction of new bio
> *
> - * Populate @bio with the data area described by @sgl. Note that
> - * the resulting bio might not contain the whole @sgl area. This
> - * can be checked by testing bio->bi_size against total area
> - * length.
> + * Populate @bio with the data area described by @sgl.
> + *
> + * RETURNS:
> + * 0 on success, -errno on failure.
> */
> -static void bio_init_from_sgl(struct bio *bio, struct request_queue *q,
> - struct scatterlist *sgl, int nents,
> - int nr_pages, int rw)
> +static int bio_init_from_sgl(struct bio *bio, struct request_queue *q,
> + struct scatterlist *sgl, int nents,
> + int nr_pages, int rw)
> {
> struct scatterlist *sg;
> int i;
> @@ -979,15 +979,18 @@ static void bio_init_from_sgl(struct bio *bio, struct request_queue *q,
> while (len) {
> size_t bytes = min_t(size_t, len, PAGE_SIZE - offset);
>
> + /* doesn't support partial mappings */
> if (unlikely(bio_add_pc_page(q, bio, page,
> bytes, offset) < bytes))
> - break;
> + return -EINVAL;
>
> offset = 0;
> len -= bytes;
> page = nth_page(page, 1);
> }
> }
> +
> + return 0;
> }
>
> /**
> @@ -1009,12 +1012,17 @@ static struct bio *bio_create_from_sgl(struct request_queue *q,
> int nr_pages, int rw, int gfp)
> {
> struct bio *bio;
> + int ret;
>
> bio = bio_kmalloc(gfp, nr_pages);
> if (!bio)
> return ERR_PTR(-ENOMEM);
>
> - bio_init_from_sgl(bio, q, sgl, nents, nr_pages, rw);
> + ret = bio_init_from_sgl(bio, q, sgl, nents, nr_pages, rw);
> + if (ret) {
> + bio_put(bio);
> + return ERR_PTR(ret);
> + }
>
> return bio;
> }
> @@ -1170,10 +1178,6 @@ struct bio *bio_map_user_iov(struct request_queue *q, struct block_device *bdev,
> goto err_pages;
> }
>
> - /* release the pages we didn't map into the bio, if any */
> - for (i = bio->bi_vcnt; i < nr_pages; i++)
> - page_cache_release(pages[i]);
> -
> bio->bi_bdev = bdev;
> bio->bi_flags |= (1 << BIO_USER_MAPPED);
>
> @@ -1283,12 +1287,6 @@ struct bio *bio_map_kern_sg(struct request_queue *q, struct scatterlist *sgl,
> if (IS_ERR(bio))
> return bio;
>
> - /* doesn't support partial mappings */
> - if (bio->bi_size != tot_len) {
> - bio_put(bio);
> - return ERR_PTR(-EINVAL);
> - }
> -
> bio->bi_end_io = bio_map_kern_endio;
> return bio;
> }
> @@ -1343,17 +1341,10 @@ struct bio *bio_copy_kern_sg(struct request_queue *q, struct scatterlist *sgl,
> goto err_bci;
> }
>
> - /* doesn't support partial mappings */
> - ret= -EINVAL;
> - if (bio->bi_size != bci->len)
> - goto err_bio;
> -
> bio->bi_end_io = bio_copy_kern_endio;
> bio->bi_private = bci;
> return bio;
>
> -err_bio:
> - bio_put(bio);
> err_bci:
> bci_destroy(bci);
> return ERR_PTR(ret);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 40bec76..6876466 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -777,7 +777,7 @@ extern int blk_rq_unmap_user(struct bio *);
> extern int blk_rq_map_kern(struct request_queue *, struct request *, void *, unsigned int, gfp_t);
> extern int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
> struct rq_map_data *md, struct iovec *iov,
> - int count, unsigned int len, gfp_t gfp);
> + int count, gfp_t gfp);
> extern int blk_rq_map_kern_sg(struct request_queue *q, struct request *rq,
> struct scatterlist *sgl, int nents, gfp_t gfp);
> extern int blk_execute_rq(struct request_queue *, struct gendisk *,

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