block: simplify bio_add_page()

Since generic_make_request() can now handle arbitrary size bios, all we
have to do is make sure the bvec array doesn't overflow.
__bio_add_page() doesn't need to call ->merge_bvec_fn(), where
we can get rid of unnecessary code paths.

Removing the call to ->merge_bvec_fn() is also fine, as no driver that
implements support for BLOCK_PC commands even has a ->merge_bvec_fn()
method.

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
[dpark: rebase and resolve merge conflicts, change a couple of comments,
 make bio_add_page() warn once upon a cloned bio.]
Signed-off-by: Dongsu Park <dpark@posteo.net>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 55 insertions, 80 deletions

diff --git a/block/bio.c b/block/bio.c
index 911ae8f82752..ba9c4b0c0ff2 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -716,9 +716,23 @@ int bio_get_nr_vecs(struct block_device *bdev)
 }
 EXPORT_SYMBOL(bio_get_nr_vecs);
 
-static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
-                          *page, unsigned int len, unsigned int offset,
-                          unsigned int max_sectors)
+/**
+ *      bio_add_pc_page -       attempt to add page to bio
+ *      @q: the target queue
+ *      @bio: destination bio
+ *      @page: page to add
+ *      @len: vec entry length
+ *      @offset: vec entry offset
+ *
+ *      Attempt to add a page to the bio_vec maplist. This can fail for a
+ *      number of reasons, such as the bio being full or target block device
+ *      limitations. The target block device must allow bio's up to PAGE_SIZE,
+ *      so it is always possible to add a single page to an empty bio.
+ *
+ *      This should only be used by REQ_PC bios.
+ */
+int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
+                    *page, unsigned int len, unsigned int offset)
 {
         int retried_segments = 0;
         struct bio_vec *bvec;
@@ -729,7 +743,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
         if (unlikely(bio_flagged(bio, BIO_CLONED)))
                 return 0;
 
-        if (((bio->bi_iter.bi_size + len) >> 9) > max_sectors)
+        if (((bio->bi_iter.bi_size + len) >> 9) > queue_max_hw_sectors(q))
                 return 0;
 
         /*
@@ -742,28 +756,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
 
                 if (page == prev->bv_page &&
                     offset == prev->bv_offset + prev->bv_len) {
-                        unsigned int prev_bv_len = prev->bv_len;
                         prev->bv_len += len;
-
-                        if (q->merge_bvec_fn) {
-                                struct bvec_merge_data bvm = {
-                                        /* prev_bvec is already charged in
-                                           bi_size, discharge it in order to
-                                           simulate merging updated prev_bvec
-                                           as new bvec. */
-                                        .bi_bdev = bio->bi_bdev,
-                                        .bi_sector = bio->bi_iter.bi_sector,
-                                        .bi_size = bio->bi_iter.bi_size -
-                                                prev_bv_len,
-                                        .bi_rw = bio->bi_rw,
-                                };
-
-                                if (q->merge_bvec_fn(q, &bvm, prev) < prev->bv_len) {
-                                        prev->bv_len -= len;
-                                        return 0;
-                                }
-                        }
-
                         bio->bi_iter.bi_size += len;
                         goto done;
                 }
@@ -806,27 +799,6 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
                 blk_recount_segments(q, bio);
         }
 
-        /*
-         * if queue has other restrictions (eg varying max sector size
-         * depending on offset), it can specify a merge_bvec_fn in the
-         * queue to get further control
-         */
-        if (q->merge_bvec_fn) {
-                struct bvec_merge_data bvm = {
-                        .bi_bdev = bio->bi_bdev,
-                        .bi_sector = bio->bi_iter.bi_sector,
-                        .bi_size = bio->bi_iter.bi_size - len,
-                        .bi_rw = bio->bi_rw,
-                };
-
-                /*
-                 * merge_bvec_fn() returns number of bytes it can accept
-                 * at this offset
-                 */
-                if (q->merge_bvec_fn(q, &bvm, bvec) < bvec->bv_len)
-                        goto failed;
-        }
-
         /* If we may be able to merge these biovecs, force a recount */
         if (bio->bi_vcnt > 1 && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec)))
                 bio_clear_flag(bio, BIO_SEG_VALID);
@@ -843,28 +815,6 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
         blk_recount_segments(q, bio);
         return 0;
 }
-
-/**
- *      bio_add_pc_page -       attempt to add page to bio
- *      @q: the target queue
- *      @bio: destination bio
- *      @page: page to add
- *      @len: vec entry length
- *      @offset: vec entry offset
- *
- *      Attempt to add a page to the bio_vec maplist. This can fail for a
- *      number of reasons, such as the bio being full or target block device
- *      limitations. The target block device must allow bio's up to PAGE_SIZE,
- *      so it is always possible to add a single page to an empty bio.
- *
- *      This should only be used by REQ_PC bios.
- */
-int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page *page,
-                    unsigned int len, unsigned int offset)
-{
-        return __bio_add_page(q, bio, page, len, offset,
-                              queue_max_hw_sectors(q));
-}
 EXPORT_SYMBOL(bio_add_pc_page);
 
 /**
@@ -874,22 +824,47 @@ EXPORT_SYMBOL(bio_add_pc_page);
  *      @len: vec entry length
  *      @offset: vec entry offset
  *
- *      Attempt to add a page to the bio_vec maplist. This can fail for a
- *      number of reasons, such as the bio being full or target block device
- *      limitations. The target block device must allow bio's up to PAGE_SIZE,
- *      so it is always possible to add a single page to an empty bio.
+ *      Attempt to add a page to the bio_vec maplist. This will only fail
+ *      if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
  */
-int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
-                 unsigned int offset)
+int bio_add_page(struct bio *bio, struct page *page,
+                 unsigned int len, unsigned int offset)
 {
-        struct request_queue *q = bdev_get_queue(bio->bi_bdev);
-        unsigned int max_sectors;
+        struct bio_vec *bv;
 
-        max_sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
-        if ((max_sectors < (len >> 9)) && !bio->bi_iter.bi_size)
-                max_sectors = len >> 9;
+        /*
+         * cloned bio must not modify vec list
+         */
+        if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
+                return 0;
 
-        return __bio_add_page(q, bio, page, len, offset, max_sectors);
+        /*
+         * For filesystems with a blocksize smaller than the pagesize
+         * we will often be called with the same page as last time and
+         * a consecutive offset.  Optimize this special case.
+         */
+        if (bio->bi_vcnt > 0) {
+                bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
+
+                if (page == bv->bv_page &&
+                    offset == bv->bv_offset + bv->bv_len) {
+                        bv->bv_len += len;
+                        goto done;
+                }
+        }
+
+        if (bio->bi_vcnt >= bio->bi_max_vecs)
+                return 0;
+
+        bv              = &bio->bi_io_vec[bio->bi_vcnt];
+        bv->bv_page     = page;
+        bv->bv_len      = len;
+        bv->bv_offset   = offset;
+
+        bio->bi_vcnt++;
+done:
+        bio->bi_iter.bi_size += len;
+        return len;
 }
 EXPORT_SYMBOL(bio_add_page);