qpolicy.c

Go to the documentation of this file.

/*
 *  net/dccp/qpolicy.c
 *
 *  Policy-based packet dequeueing interface for DCCP.
 *
 *  Copyright (c) 2008 Tomasz Grobelny <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License v2
 *  as published by the Free Software Foundation.
 */
#include "dccp.h"

/*
 *  Simple Dequeueing Policy:
 *  If tx_qlen is different from 0, enqueue up to tx_qlen elements.
 */
static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
{
    skb_queue_tail(&sk->sk_write_queue, skb);
}

static bool qpolicy_simple_full(struct sock *sk)
{
    return dccp_sk(sk)->dccps_tx_qlen &&
           sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
}

static struct sk_buff *qpolicy_simple_top(struct sock *sk)
{
    return skb_peek(&sk->sk_write_queue);
}

/*
 *  Priority-based Dequeueing Policy:
 *  If tx_qlen is different from 0 and the queue has reached its upper bound
 *  of tx_qlen elements, replace older packets lowest-priority-first.
 */
static struct sk_buff *qpolicy_prio_best_skb(struct sock *sk)
{
    struct sk_buff *skb, *best = NULL;

    skb_queue_walk(&sk->sk_write_queue, skb)
        if (best == NULL || skb->priority > best->priority)
            best = skb;
    return best;
}

static struct sk_buff *qpolicy_prio_worst_skb(struct sock *sk)
{
    struct sk_buff *skb, *worst = NULL;

    skb_queue_walk(&sk->sk_write_queue, skb)
        if (worst == NULL || skb->priority < worst->priority)
            worst = skb;
    return worst;
}

static bool qpolicy_prio_full(struct sock *sk)
{
    if (qpolicy_simple_full(sk))
        dccp_qpolicy_drop(sk, qpolicy_prio_worst_skb(sk));
    return false;
}

static struct dccp_qpolicy_operations {
    void        (*push) (struct sock *sk, struct sk_buff *skb);
    bool        (*full) (struct sock *sk);
    struct sk_buff* (*top)  (struct sock *sk);
    __be32      params;

} qpol_table[DCCPQ_POLICY_MAX] = {
    [DCCPQ_POLICY_SIMPLE] = {
        .push   = qpolicy_simple_push,
        .full   = qpolicy_simple_full,
        .top    = qpolicy_simple_top,
        .params = 0,
    },
    [DCCPQ_POLICY_PRIO] = {
        .push   = qpolicy_simple_push,
        .full   = qpolicy_prio_full,
        .top    = qpolicy_prio_best_skb,
        .params = DCCP_SCM_PRIORITY,
    },
};

/*
 *  Externally visible interface
 */
void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
{
    qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
}

bool dccp_qpolicy_full(struct sock *sk)
{
    return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
}

void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
{
    if (skb != NULL) {
        skb_unlink(skb, &sk->sk_write_queue);
        kfree_skb(skb);
    }
}

struct sk_buff *dccp_qpolicy_top(struct sock *sk)
{
    return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
}

struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
{
    struct sk_buff *skb = dccp_qpolicy_top(sk);

    if (skb != NULL) {
        /* Clear any skb fields that we used internally */
        skb->priority = 0;
        skb_unlink(skb, &sk->sk_write_queue);
    }
    return skb;
}

bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param)
{
    /* check if exactly one bit is set */
    if (!param || (param & (param - 1)))
        return false;
    return (qpol_table[dccp_sk(sk)->dccps_qpolicy].params & param) == param;
}