commit 542af9092c905bf9bf12cdca04549827fab36c52
Author: David Gwynne <dlg@uq.edu.au>
Date:   Tue Feb 24 16:20:05 2015 +1000

    provide functions to requeue mbufs on mbuf_queues or mbuf_lists,
    and to requeue mbuf_lists on mbuf_queues.

diff --git a/share/man/man9/mbuf.9 b/share/man/man9/mbuf.9
index dc90145..8ba36b9 100644
--- a/share/man/man9/mbuf.9
+++ b/share/man/man9/mbuf.9
@@ -117,6 +117,8 @@
 .Fn "ml_enqueue" "struct mbuf_list *ml" "struct mbuf *m"
 .Ft struct mbuf *
 .Fn "ml_dequeue" "struct mbuf_list *ml"
+.Ft void
+.Fn "ml_requeue" "struct mbuf_list *ml" "struct mbuf *m"
 .Ft struct mbuf *
 .Fn "ml_dechain" "struct mbuf_list *ml"
 .Ft struct mbuf *
@@ -138,9 +140,13 @@
 .Ft struct mbuf *
 .Fn "mq_dequeue" "struct mbuf_queue *mq"
 .Ft int
+.Fn "mq_requeue" "struct mbuf_queue *mq" "struct mbuf *m"
+.Ft int
 .Fn "mq_enlist" "struct mbuf_queue *mq" "struct mbuf_list *ml"
 .Ft void
 .Fn "mq_delist" "struct mbuf_queue *mq" "struct mbuf_list *ml"
+.Ft int
+.Fn "mq_relist" "struct mbuf_queue *mq" "struct mbuf_list *ml"
 .Ft struct mbuf *
 .Fn "mq_dechain" "struct mbuf_queue *mq"
 .Ft struct mbuf *
@@ -789,6 +795,12 @@ mbuf list.
 Dequeue an mbuf from the front of the
 .Fa ml
 mbuf list.
+.It Fn "ml_requeue" "struct mbuf_list *ml" "struct mbuf *m"
+Enqueue mbuf
+.Fa m
+at the head of the
+.Fa ml
+mbuf list.
 .It Fn "ml_dechain" "struct mbuf_list *ml"
 Dequeues all mbufs from the
 .Fa ml
@@ -870,6 +882,14 @@ mbuf queue.
 Dequeue an mbuf from the front of the
 .Fa mq
 mbuf queue.
+.It Fn "mq_requeue" "struct mbuf_queue *mq" "struct mbuf *m"
+Enqueue mbuf
+.Fa m
+at the head of the
+.Fa mq
+mbuf queue.
+Note, this operation will succeed even if it will cause the queue to exceed its
+maximum length.
 .It Fn "mq_enlist" "struct mbuf_queue *mq" "struct mbuf_list *ml"
 Enqueue all the mbufs on the
 .Fa ml
@@ -883,6 +903,14 @@ Dequeue all the mbufs on the
 mbuf queue on to the
 .Fa ml
 mbuf list.
+.It Fn "mq_relist" "struct mbuf_queue *mq" "struct mbuf_list *ml"
+Enqueue all the mbufs on the
+.Fa ml
+mbuf list at the head of the
+.Fa mq
+mbuf queue.
+Note, this operation will succeed even if it will cause the queue to exceed its
+maximum length.
 .It Fn "mq_dechain" "struct mbuf_queue *mq"
 Dequeue all mbufs from the
 .Fa mq
@@ -933,6 +961,7 @@ already exist on the queue.
 .Fn ml_init ,
 .Fn ml_enqueue ,
 .Fn ml_dequeue ,
+.Fn ml_requeue ,
 .Fn ml_dechain ,
 .Fn ml_len ,
 .Fn ml_empty ,
@@ -941,8 +970,10 @@ already exist on the queue.
 .Fn mq_init ,
 .Fn mq_enqueue ,
 .Fn mq_dequeue ,
+.Fn mq_requeue ,
 .Fn mq_enlist ,
 .Fn mq_delist ,
+.Fn mq_relist ,
 .Fn mq_dechain ,
 .Fn mq_len ,
 .Fn mq_empty ,
@@ -994,10 +1025,17 @@ returns 0 if the mbuf was successfully queued, or non-zero if the
 mbuf was freed because it would cause the queue to exceed its maximum
 length.
 .Pp
+.Fn mq_requeue
+returns non-zero if the mbuf queue is full, otherwise 0.
+length.
+.Pp
 .Fn mq_enlist
 returns the number of mbufs that were dropped from the list if the
 length of the queue exceeded its maximum length.
 .Pp
+.Fn mq_relist
+returns non-zero if the mbuf queue is now full, otherwise 0.
+.Pp
 .Fn mq_drops
 returns the number of mbufs that were freed during
 .Fn mq_enqueue
diff --git a/sys/kern/uipc_mbuf.c b/sys/kern/uipc_mbuf.c
index c17c810..1a9cd03 100644
--- a/sys/kern/uipc_mbuf.c
+++ b/sys/kern/uipc_mbuf.c
@@ -1297,6 +1297,19 @@ ml_dequeue(struct mbuf_list *ml)
 	return (m);
 }
 
+void
+ml_requeue(struct mbuf_list *ml, struct mbuf *m)
+{
+	if (ml->ml_tail == NULL)
+		ml->ml_head = ml->ml_tail = m;
+	else {
+		m->m_nextpkt = ml->ml_head;
+		ml->ml_head = m;
+	}
+
+	ml->ml_len++;
+}
+
 struct mbuf *
 ml_dechain(struct mbuf_list *ml)
 {
@@ -1383,6 +1396,19 @@ mq_dequeue(struct mbuf_queue *mq)
 }
 
 int
+mq_requeue(struct mbuf_queue *mq, struct mbuf *m)
+{
+	int full;
+
+	mtx_enter(&mq->mq_mtx);
+	ml_requeue(&mq->mq_list, m);
+	full = mq_len(mq) >= mq->mq_maxlen;
+	mtx_leave(&mq->mq_mtx);
+
+	return (full);
+}
+
+int
 mq_enlist(struct mbuf_queue *mq, struct mbuf_list *ml)
 {
 	struct mbuf *m;
@@ -1414,6 +1440,28 @@ mq_delist(struct mbuf_queue *mq, struct mbuf_list *ml)
 	mtx_leave(&mq->mq_mtx);
 }
 
+int
+mq_relist(struct mbuf_queue *mq, struct mbuf_list *ml)
+{
+	int full;
+
+	if (ml_empty(ml))
+		return (mq_len(mq) > mq->mq_maxlen);
+
+	mtx_enter(&mq->mq_mtx);
+	if (ml_empty(&mq->mq_list))
+		mq->mq_list = *ml;
+	else {
+		ml->ml_tail->m_nextpkt = mq->mq_list.ml_head;
+		mq->mq_list.ml_head = ml->ml_head;
+		mq->mq_list.ml_len += ml->ml_len;
+	}
+	full = mq_len(mq) > mq->mq_maxlen;
+	mtx_leave(&mq->mq_mtx);
+
+	return (full);
+}
+
 struct mbuf *
 mq_dechain(struct mbuf_queue *mq)
 {
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
index b813d6b..34fe78e 100644
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -496,6 +496,7 @@ struct mbuf_list {
 void			ml_init(struct mbuf_list *);
 void			ml_enqueue(struct mbuf_list *, struct mbuf *);
 struct mbuf *		ml_dequeue(struct mbuf_list *);
+void			ml_requeue(struct mbuf_list *, struct mbuf *);
 struct mbuf *		ml_dechain(struct mbuf_list *);
 struct mbuf *		ml_filter(struct mbuf_list *,
 			    int (*)(void *, const struct mbuf *), void *);
@@ -523,8 +524,10 @@ struct mbuf_queue {
 void			mq_init(struct mbuf_queue *, u_int, int);
 int			mq_enqueue(struct mbuf_queue *, struct mbuf *);
 struct mbuf *		mq_dequeue(struct mbuf_queue *);
+int			mq_requeue(struct mbuf_queue *, struct mbuf *);
 int			mq_enlist(struct mbuf_queue *, struct mbuf_list *);
 void			mq_delist(struct mbuf_queue *, struct mbuf_list *);
+int			mq_relist(struct mbuf_queue *, struct mbuf_list *);
 struct mbuf *		mq_dechain(struct mbuf_queue *);
 struct mbuf *		mq_filter(struct mbuf_queue *,
 			    int (*)(void *, const struct mbuf *), void *);