[SCSI] block: fix the partial mappings with struct rq_map_data

This fixes bio_copy_user_iov to properly handle the partial mappings
with struct rq_map_data (which only sg uses for now but st and osst
will shortly). It adds the offset member to struct rq_map_data and
changes blk_rq_map_user to update it so that bio_copy_user_iov can add
an appropriate page frame via bio_add_pc_page().

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

4 files changed, 14 insertions, 3 deletions

diff --git a/block/blk-map.c b/block/blk-map.c
index 2990447f45e9..c7e55b23a2bc 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -150,6 +150,9 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
                         bio = rq->bio;
                 bytes_read += ret;
                 ubuf += ret;
+
+                if (map_data)
+                        map_data->offset += ret;
         }
 
         if (!bio_flagged(bio, BIO_USER_MAPPED))
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 5103855242ae..7d0b3d9ee43b 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1669,6 +1669,7 @@ static int sg_start_req(Sg_request *srp, unsigned char *cmd)
                 md->pages = req_schp->pages;
                 md->page_order = req_schp->page_order;
                 md->nr_entries = req_schp->k_use_sg;
+                md->offset = 0;
         }
 
         if (iov_count)
diff --git a/fs/bio.c b/fs/bio.c
index 356e7423b923..13be075806b6 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -788,6 +788,7 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
         int i, ret;
         int nr_pages = 0;
         unsigned int len = 0;
+        unsigned int offset = map_data ? map_data->offset & ~PAGE_MASK : 0;
 
         for (i = 0; i < iov_count; i++) {
                 unsigned long uaddr;
@@ -814,12 +815,16 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
         bio->bi_rw |= (!write_to_vm << BIO_RW);
 
         ret = 0;
-        i = 0;
-        if (map_data)
+
+        if (map_data) {
                 nr_pages = 1 << map_data->page_order;
+                i = map_data->offset / PAGE_SIZE;
+        }
         while (len) {
                 unsigned int bytes = PAGE_SIZE;
 
+                bytes -= offset;
+
                 if (bytes > len)
                         bytes = len;
 
@@ -841,10 +846,11 @@ struct bio *bio_copy_user_iov(struct request_queue *q,
                         }
                 }
 
-                if (bio_add_pc_page(q, bio, page, bytes, 0) < bytes)
+                if (bio_add_pc_page(q, bio, page, bytes, offset) < bytes)
                         break;
 
                 len -= bytes;
+                offset = 0;
         }
 
         if (ret)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7035cec583b6..811e5342c452 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -690,6 +690,7 @@ struct rq_map_data {
         struct page **pages;
         int page_order;
         int nr_entries;
+        unsigned long offset;
 };
 
 struct req_iterator {