net/sched: sch_plug - Queue traffic until an explicit release command

The qdisc supports two operations - plug and unplug. When the
qdisc receives a plug command via netlink request, packets arriving
henceforth are buffered until a corresponding unplug command is received.
Depending on the type of unplug command, the queue can be unplugged
indefinitely or selectively.

This qdisc can be used to implement output buffering, an essential
functionality required for consistent recovery in checkpoint based
fault-tolerance systems. Output buffering enables speculative execution
by allowing generated network traffic to be rolled back. It is used to
provide network protection for Xen Guests in the Remus high availability
project, available as part of Xen.

This module is generic enough to be used by any other system that wishes
to add speculative execution and output buffering to its applications.

This module was originally available in the linux 2.6.32 PV-OPS tree,
used as dom0 for Xen.

For more information, please refer to http://nss.cs.ubc.ca/remus/
and http://wiki.xensource.com/xenwiki/Remus

Changes in V3:
  * Removed debug output (printk) on queue overflow
  * Added TCQ_PLUG_RELEASE_INDEFINITE - that allows the user to
    use this qdisc, for simple plug/unplug operations.
  * Use of packet counts instead of pointers to keep track of
    the buffers in the queue.

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Signed-off-by: Brendan Cully <brendan@cs.ubc.ca>
[author of the code in the linux 2.6.32 pvops tree]
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 0d5b79365d03..410b33d014d2 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -127,6 +127,27 @@ struct tc_multiq_qopt {
 	__u16	max_bands;		/* Maximum number of queues */
 };
 
+/* PLUG section */
+
+#define TCQ_PLUG_BUFFER                0
+#define TCQ_PLUG_RELEASE_ONE           1
+#define TCQ_PLUG_RELEASE_INDEFINITE    2
+#define TCQ_PLUG_LIMIT                 3
+
+struct tc_plug_qopt {
+	/* TCQ_PLUG_BUFFER: Inset a plug into the queue and
+	 *  buffer any incoming packets
+	 * TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head
+	 *   to beginning of the next plug.
+	 * TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue.
+	 *   Stop buffering packets until the next TCQ_PLUG_BUFFER
+	 *   command is received (just act as a pass-thru queue).
+	 * TCQ_PLUG_LIMIT: Increase/decrease queue size
+	 */
+	int             action;
+	__u32           limit;
+};
+
 /* TBF section */
 
 struct tc_tbf_qopt {