linux-imx

/*

 * sch_plug.c Queue traffic until an explicit release command

 *

 *             This program is free software; you can redistribute it and/or

 *             modify it under the terms of the GNU General Public License

 *             as published by the Free Software Foundation; either version

 *             2 of the License, or (at your option) any later version.

 *

 * There are two ways to use this qdisc:

 * 1. A simple "instantaneous" plug/unplug operation, by issuing an alternating

 *    sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands.

 *

 * 2. 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)

 *       2. 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

 *       3. While speculatively executing epoch(i+1), asynchronously replicate

 *          checkpoint(i) to backup host.

 *       4. 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)

 *       ........

 */

​

#include <linux/module.h>

#include <linux/types.h>

#include <linux/kernel.h>

#include <linux/errno.h>

#include <linux/netdevice.h>

#include <linux/skbuff.h>

#include <net/pkt_sched.h>

​

/*

 * 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

 *

 */

​

struct plug_sched_data {

    /* If true, the dequeue function releases all packets

     * from head to end of the queue. The queue turns into

     * a pass-through queue for newly arriving packets.