On Tue, Oct 24, 2017 at 11:44:26AM +0300, Max Gurtovoy wrote:

quoted

+ * Steal bios from a request.  The request must not have been partially
+ * completed before.
+ */

Maybe we can add to the comment that "list" is the destination for the 
stolen bio.

Sure.

quoted

+void blk_steal_bios(struct bio_list *list, struct request *rq)
+{
+	if (rq->bio) {
+		if (list->tail)
+			list->tail->bi_next = rq->bio;
+		else
+			list->head = rq->bio;
+		list->tail = rq->biotail;

if list->tail != NULL don't we lose the "list->tail->bi_next = rq->bio;" 
assignment after assigning "list->tail = rq->biotail;" ?

the biolists are a little weird, they are a single linked list of bi_next
plus a tail pointer.

So if the list is emptry (->tail == NULL) we assign the biolist
to ->head and point ->tail to end of the list in the request.

But if the list is not empty we let ->bi_next of the last entry
(as found in ->tail) point to the list we splice on, and still update
->tail to end of the list we spliced on.  So I think this looks all ok.

quoted

+	}
+
+	rq->bio = NULL;

we can add this NULL assignment inside the big "if", but I'm not sure 
regarding the next 2 assignments.
Anyway not a big deal.

We can move both the ->bio and ->biotail assignments, and I've done it.