Queue traffic until an explicit release command. More...

Attribute Modification
int	rtnl_qdisc_plug_buffer (struct rtnl_qdisc *qdisc)
	Insert a plug into the qdisc and buffer any incoming network traffic. More...

int	rtnl_qdisc_plug_release_one (struct rtnl_qdisc *qdisc)
	Unplug the qdisc, releasing packets from queue head to the last complete buffer, while new traffic continues to be buffered. More...

int	rtnl_qdisc_plug_release_indefinite (struct rtnl_qdisc *qdisc)
	Indefinitely unplug the qdisc, releasing all packets. More...

int	rtnl_qdisc_plug_set_limit (struct rtnl_qdisc *qdisc, int limit)
	Set limit of PLUG qdisc. More...

Detailed Description

Queue traffic until an explicit release command.

There are two ways to use this qdisc:

A simple "instantaneous" plug/unplug operation, by issuing an alternating sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands.

For network output buffering (a.k.a output commit) functionality. Output commit property is commonly used by applications using checkpoint based fault-tolerance to ensure that the checkpoint from which a system is being restored is consistent w.r.t outside world.

Consider for e.g. Remus - a Virtual Machine checkpointing system, wherein a VM is checkpointed, say every 50ms. The checkpoint is replicated asynchronously to the backup host, while the VM continues executing the next epoch speculatively.

The following is a typical sequence of output buffer operations: 1.At epoch i, start_buffer(i)
1. At end of epoch i (i.e. after 50ms): 2.1 Stop VM and take checkpoint(i). 2.2 start_buffer(i+1) and Resume VM
2. While speculatively executing epoch(i+1), asynchronously replicate checkpoint(i) to backup host.
3. When checkpoint_ack(i) is received from backup, release_buffer(i) Thus, this Qdisc would receive the following sequence of commands: TCQ_PLUG_BUFFER (epoch i) .. TCQ_PLUG_BUFFER (epoch i+1) ....TCQ_PLUG_RELEASE_ONE (epoch i) ......TCQ_PLUG_BUFFER (epoch i+2) ........

State of the queue, when used for network output buffering:

            plug(i+1)            plug(i)          head

---------------—+-----------------—+-------------—> | | | | pkts_current_epoch| pkts_last_epoch |pkts_to_release --------------—>|<-----—+------—>|+------------—> v v