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>

diff --git a/block/bio.c b/block/bio.c
index 2b375020fc49bab0bfcabda4fc3d16118b5f1512..9e2b33ddca0a774fbb5b0098611fbc1d9cd53967 100644 (file)
--- 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;
        }
@@ -699,8 +699,43 @@ 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

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7cf8a6c70a3f71c5eca6100dfda8d67f10b20e3b..8e521194f6fc4ad32138a51c962a365c74debaed 100644 (file)
--- 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;