block: Add bio_copy_data()

This gets open coded quite a bit and it's tricky to get right, so make a
generic version and convert some existing users over to it instead.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Jens Axboe <axboe@kernel.dk>

1 files changed, 70 insertions, 0 deletions

diff --git a/fs/bio.c b/fs/bio.c
index 4ce24ee5dcd0..e437f9aae67d 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -829,6 +829,76 @@ void bio_advance(struct bio *bio, unsigned bytes)
 }
 EXPORT_SYMBOL(bio_advance);
 
+/**
+ * bio_copy_data - copy contents of data buffers from one chain of bios to
+ * another
+ * @src: source bio list
+ * @dst: destination bio list
+ *
+ * If @src and @dst are single bios, bi_next must be NULL - otherwise, treats
+ * @src and @dst as linked lists of bios.
+ *
+ * Stops when it reaches the end of either @src or @dst - that is, copies
+ * min(src->bi_size, dst->bi_size) bytes (or the equivalent for lists of bios).
+ */
+void bio_copy_data(struct bio *dst, struct bio *src)
+{
+        struct bio_vec *src_bv, *dst_bv;
+        unsigned src_offset, dst_offset, bytes;
+        void *src_p, *dst_p;
+
+        src_bv = bio_iovec(src);
+        dst_bv = bio_iovec(dst);
+
+        src_offset = src_bv->bv_offset;
+        dst_offset = dst_bv->bv_offset;
+
+        while (1) {
+                if (src_offset == src_bv->bv_offset + src_bv->bv_len) {
+                        src_bv++;
+                        if (src_bv == bio_iovec_idx(src, src->bi_vcnt)) {
+                                src = src->bi_next;
+                                if (!src)
+                                        break;
+
+                                src_bv = bio_iovec(src);
+                        }
+
+                        src_offset = src_bv->bv_offset;
+                }
+
+                if (dst_offset == dst_bv->bv_offset + dst_bv->bv_len) {
+                        dst_bv++;
+                        if (dst_bv == bio_iovec_idx(dst, dst->bi_vcnt)) {
+                                dst = dst->bi_next;
+                                if (!dst)
+                                        break;
+
+                                dst_bv = bio_iovec(dst);
+                        }
+
+                        dst_offset = dst_bv->bv_offset;
+                }
+
+                bytes = min(dst_bv->bv_offset + dst_bv->bv_len - dst_offset,
+                            src_bv->bv_offset + src_bv->bv_len - src_offset);
+
+                src_p = kmap_atomic(src_bv->bv_page);
+                dst_p = kmap_atomic(dst_bv->bv_page);
+
+                memcpy(dst_p + dst_bv->bv_offset,
+                       src_p + src_bv->bv_offset,
+                       bytes);
+
+                kunmap_atomic(dst_p);
+                kunmap_atomic(src_p);
+
+                src_offset += bytes;
+                dst_offset += bytes;
+        }
+}
+EXPORT_SYMBOL(bio_copy_data);
+
 struct bio_map_data {
         struct bio_vec *iovecs;
         struct sg_iovec *sgvecs;