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>

diff --git a/fs/bio.c b/fs/bio.c
index 4ce24ee..e437f9a 100644 (file)
--- 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;

diff --git a/include/linux/bio.h b/include/linux/bio.h
index b20a9cd..90d36c6 100644 (file)
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -286,6 +286,8 @@ static inline void bio_flush_dcache_pages(struct bio *bi)
 }
 #endif
 
+extern void bio_copy_data(struct bio *dst, struct bio *src);
+
 extern struct bio *bio_copy_user(struct request_queue *, struct rq_map_data *,
                                 unsigned long, unsigned int, int, gfp_t);
 extern struct bio *bio_copy_user_iov(struct request_queue *,