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    SubjectRe: [PATCH 16/17] blk-map/bio: remove superflous @len parameter from blk_rq_map_user_iov()
    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@kernel.org>
    > ---
    > 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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