Btrfs: new helper btrfs_bio_clone_partial

This adds a new helper btrfs_bio_clone_partial, it'll allocate a cloned
bio that only owns a part of the original bio's data.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 292e458..db2bbf9 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2720,6 +2720,24 @@ struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
        return bio;
 }
 
+struct bio *btrfs_bio_clone_partial(struct bio *orig, gfp_t gfp_mask,
+                                   int offset, int size)
+{
+       struct bio *bio;
+       struct btrfs_io_bio *btrfs_bio;
+
+       /* this will never fail when it's backed by a bioset */
+       bio = bio_clone_fast(orig, gfp_mask, btrfs_bioset);
+       ASSERT(bio);
+
+       btrfs_bio = btrfs_io_bio(bio);
+       btrfs_bio->csum = NULL;
+       btrfs_bio->csum_allocated = NULL;
+       btrfs_bio->end_io = NULL;
+
+       bio_trim(bio, offset >> 9, size >> 9);
+       return bio;
+}
 
 static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
                                       unsigned long bio_flags)

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 1383afd..3df0185 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -467,6 +467,8 @@ btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
                gfp_t gfp_flags);
 struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs);
 struct bio *btrfs_bio_clone(struct bio *bio, gfp_t gfp_mask);
+struct bio *btrfs_bio_clone_partial(struct bio *orig, gfp_t gfp_mask,
+                                   int offset, int size);
 
 struct btrfs_fs_info;
 struct btrfs_inode;