From: Liu Bo <bo.li.liu@oracle.com>
Date: Mon, 15 May 2017 17:43:31 -0700
Subject: [PATCH] Btrfs: new helper btrfs_bio_clone_partial
Git-commit: 2f8e9140426dff6091b7a40d441befc791882658
Patch-Mainline: v4.13-rc1
References: FATE#323952, FATE#322506

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>
Acked-by: Hannes Reinecke <hare@suse.de>
---
 fs/btrfs/extent_io.c | 18 ++++++++++++++++++
 fs/btrfs/extent_io.h |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 33cc67e..b895c79 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2742,6 +2742,24 @@ 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 89ac1f7..74778a1 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -463,6 +463,8 @@ struct bio *
 		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;
-- 
1.8.5.6