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, 26 insertions, 0 deletions

diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 2590e91b328..75b58f81d53 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -260,6 +260,32 @@ config NET_SCH_INGRESS
           To compile this code as a module, choose M here: the
           module will be called sch_ingress.
 
+config NET_SCH_PLUG
+        tristate "Plug network traffic until release (PLUG)"
+        ---help---
+
+          This queuing discipline allows userspace to plug/unplug a network
+          output queue, using the netlink interface.  When it receives an
+          enqueue command it inserts a plug into the outbound queue that
+          causes following packets to enqueue until a dequeue command arrives
+          over netlink, causing the plug to be removed and resuming the normal
+          packet flow.
+
+          This module also provides a generic "network output buffering"
+          functionality (aka output commit), wherein upon arrival of a dequeue
+          command, only packets up to the first plug are released for delivery.
+          The Remus HA project uses this module to enable speculative execution
+          of virtual machines by allowing the generated network output to be rolled
+          back if needed.
+
+          For more information, please refer to http://wiki.xensource.com/xenwiki/Remus
+
+          Say Y here if you are using this kernel for Xen dom0 and
+          want to protect Xen guests with Remus.
+
+          To compile this code as a module, choose M here: the
+          module will be called sch_plug.
+
 comment "Classification"
 
 config NET_CLS