1 files changed, 52 insertions, 1 deletions

diff --git a/block/bio.c b/block/bio.c
index 9d54aa37ce6c..94d697217887 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -539,6 +539,55 @@ void zero_fill_bio_iter(struct bio *bio, struct bvec_iter start)
 EXPORT_SYMBOL(zero_fill_bio_iter);
 
 /**
+ * bio_truncate - truncate the bio to small size of @new_size
+ * @bio:	the bio to be truncated
+ * @new_size:	new size for truncating the bio
+ *
+ * Description:
+ *   Truncate the bio to new size of @new_size. If bio_op(bio) is
+ *   REQ_OP_READ, zero the truncated part. This function should only
+ *   be used for handling corner cases, such as bio eod.
+ */
+void bio_truncate(struct bio *bio, unsigned new_size)
+{
+	struct bio_vec bv;
+	struct bvec_iter iter;
+	unsigned int done = 0;
+	bool truncated = false;
+
+	if (new_size >= bio->bi_iter.bi_size)
+		return;
+
+	if (bio_op(bio) != REQ_OP_READ)
+		goto exit;
+
+	bio_for_each_segment(bv, bio, iter) {
+		if (done + bv.bv_len > new_size) {
+			unsigned offset;
+
+			if (!truncated)
+				offset = new_size - done;
+			else
+				offset = 0;
+			zero_user(bv.bv_page, offset, bv.bv_len - offset);
+			truncated = true;
+		}
+		done += bv.bv_len;
+	}
+
+ exit:
+	/*
+	 * Don't touch bvec table here and make it really immutable, since
+	 * fs bio user has to retrieve all pages via bio_for_each_segment_all
+	 * in its .end_bio() callback.
+	 *
+	 * It is enough to truncate bio by updating .bi_size since we can make
+	 * correct bvec with the updated .bi_size for drivers.
+	 */
+	bio->bi_iter.bi_size = new_size;
+}
+
+/**
  * bio_put - release a reference to a bio
  * @bio:   bio to release reference to
  *
@@ -754,10 +803,12 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
 		return false;
 
-	if (bio->bi_vcnt > 0 && !bio_full(bio, len)) {
+	if (bio->bi_vcnt > 0) {
 		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
 		if (page_is_mergeable(bv, page, len, off, same_page)) {
+			if (bio->bi_iter.bi_size > UINT_MAX - len)
+				return false;
 			bv->bv_len += len;
 			bio->bi_iter.bi_size += len;
 			return true;