block: introduce bio_clone_bioset_partial()

md still need bio clone(not the fast version) for behind write,
and it is more efficient to use bio_clone_bioset_partial().

The idea is simple and just copy the bvecs range specified from
parameters.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Shaohua Li <shli@fb.com>

2 files changed, 57 insertions, 15 deletions

diff --git a/block/bio.c b/block/bio.c
index 2b375020fc49..9e2b33ddca0a 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -625,21 +625,20 @@ struct bio *bio_clone_fast(struct bio *bio, gfp_t gfp_mask, struct bio_set *bs)
 }
 EXPORT_SYMBOL(bio_clone_fast);
 
-/**
- *      bio_clone_bioset - clone a bio
- *      @bio_src: bio to clone
- *      @gfp_mask: allocation priority
- *      @bs: bio_set to allocate from
- *
- *      Clone bio. Caller will own the returned bio, but not the actual data it
- *      points to. Reference count of returned bio will be one.
- */
-struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
-                             struct bio_set *bs)
+static struct bio *__bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+                                      struct bio_set *bs, int offset,
+                                      int size)
 {
         struct bvec_iter iter;
         struct bio_vec bv;
         struct bio *bio;
+        struct bvec_iter iter_src = bio_src->bi_iter;
+
+        /* for supporting partial clone */
+        if (offset || size != bio_src->bi_iter.bi_size) {
+                bio_advance_iter(bio_src, &iter_src, offset);
+                iter_src.bi_size = size;
+        }
 
         /*
          * Pre immutable biovecs, __bio_clone() used to just do a memcpy from
@@ -663,7 +662,8 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
          *    __bio_clone_fast() anyways.
          */
 
-        bio = bio_alloc_bioset(gfp_mask, bio_segments(bio_src), bs);
+        bio = bio_alloc_bioset(gfp_mask, __bio_segments(bio_src,
+                               &iter_src), bs);
         if (!bio)
                 return NULL;
         bio->bi_bdev            = bio_src->bi_bdev;
@@ -680,7 +680,7 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
                 bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
                 break;
         default:
-                bio_for_each_segment(bv, bio_src, iter)
+                __bio_for_each_segment(bv, bio_src, iter, iter_src)
                         bio->bi_io_vec[bio->bi_vcnt++] = bv;
                 break;
         }
@@ -699,9 +699,44 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
 
         return bio;
 }
+
+/**
+ *      bio_clone_bioset - clone a bio
+ *      @bio_src: bio to clone
+ *      @gfp_mask: allocation priority
+ *      @bs: bio_set to allocate from
+ *
+ *      Clone bio. Caller will own the returned bio, but not the actual data it
+ *      points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
+                             struct bio_set *bs)
+{
+        return __bio_clone_bioset(bio_src, gfp_mask, bs, 0,
+                                  bio_src->bi_iter.bi_size);
+}
 EXPORT_SYMBOL(bio_clone_bioset);
 
 /**
+ *      bio_clone_bioset_partial - clone a partial bio
+ *      @bio_src: bio to clone
+ *      @gfp_mask: allocation priority
+ *      @bs: bio_set to allocate from
+ *      @offset: cloned starting from the offset
+ *      @size: size for the cloned bio
+ *
+ *      Clone bio. Caller will own the returned bio, but not the actual data it
+ *      points to. Reference count of returned bio will be one.
+ */
+struct bio *bio_clone_bioset_partial(struct bio *bio_src, gfp_t gfp_mask,
+                                     struct bio_set *bs, int offset,
+                                     int size)
+{
+        return __bio_clone_bioset(bio_src, gfp_mask, bs, offset, size);
+}
+EXPORT_SYMBOL(bio_clone_bioset_partial);
+
+/**
  *      bio_add_pc_page -       attempt to add page to bio
  *      @q: the target queue
  *      @bio: destination bio
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7cf8a6c70a3f..8e521194f6fc 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -183,7 +183,7 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 
 #define bio_iter_last(bvec, iter) ((iter).bi_size == (bvec).bv_len)
 
-static inline unsigned bio_segments(struct bio *bio)
+static inline unsigned __bio_segments(struct bio *bio, struct bvec_iter *bvec)
 {
         unsigned segs = 0;
         struct bio_vec bv;
@@ -205,12 +205,17 @@ static inline unsigned bio_segments(struct bio *bio)
                 break;
         }
 
-        bio_for_each_segment(bv, bio, iter)
+        __bio_for_each_segment(bv, bio, iter, *bvec)
                 segs++;
 
         return segs;
 }
 
+static inline unsigned bio_segments(struct bio *bio)
+{
+        return __bio_segments(bio, &bio->bi_iter);
+}
+
 /*
  * get a reference to a bio, so it won't disappear. the intended use is
  * something like:
@@ -384,6 +389,8 @@ extern void bio_put(struct bio *);
 extern void __bio_clone_fast(struct bio *, struct bio *);
 extern struct bio *bio_clone_fast(struct bio *, gfp_t, struct bio_set *);
 extern struct bio *bio_clone_bioset(struct bio *, gfp_t, struct bio_set *bs);
+extern struct bio *bio_clone_bioset_partial(struct bio *, gfp_t,
+                                            struct bio_set *, int, int);
 
 extern struct bio_set *fs_bio_set;