1/*
2 *  net/dccp/qpolicy.c
3 *
4 *  Policy-based packet dequeueing interface for DCCP.
5 *
6 *  Copyright (c) 2008 Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
7 *
8 *  This program is free software; you can redistribute it and/or
9 *  modify it under the terms of the GNU General Public License v2
10 *  as published by the Free Software Foundation.
11 */
12#include "dccp.h"
13
14/*
15 *	Simple Dequeueing Policy:
16 *	If tx_qlen is different from 0, enqueue up to tx_qlen elements.
17 */
18static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
19{
20	skb_queue_tail(&sk->sk_write_queue, skb);
21}
22
23static bool qpolicy_simple_full(struct sock *sk)
24{
25	return dccp_sk(sk)->dccps_tx_qlen &&
26	       sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
27}
28
29static struct sk_buff *qpolicy_simple_top(struct sock *sk)
30{
31	return skb_peek(&sk->sk_write_queue);
32}
33
34/*
35 *	Priority-based Dequeueing Policy:
36 *	If tx_qlen is different from 0 and the queue has reached its upper bound
37 *	of tx_qlen elements, replace older packets lowest-priority-first.
38 */
39static struct sk_buff *qpolicy_prio_best_skb(struct sock *sk)
40{
41	struct sk_buff *skb, *best = NULL;
42
43	skb_queue_walk(&sk->sk_write_queue, skb)
44		if (best == NULL || skb->priority > best->priority)
45			best = skb;
46	return best;
47}
48
49static struct sk_buff *qpolicy_prio_worst_skb(struct sock *sk)
50{
51	struct sk_buff *skb, *worst = NULL;
52
53	skb_queue_walk(&sk->sk_write_queue, skb)
54		if (worst == NULL || skb->priority < worst->priority)
55			worst = skb;
56	return worst;
57}
58
59static bool qpolicy_prio_full(struct sock *sk)
60{
61	if (qpolicy_simple_full(sk))
62		dccp_qpolicy_drop(sk, qpolicy_prio_worst_skb(sk));
63	return false;
64}
65
66/**
67 * struct dccp_qpolicy_operations  -  TX Packet Dequeueing Interface
68 * @push: add a new @skb to the write queue
69 * @full: indicates that no more packets will be admitted
70 * @top:  peeks at whatever the queueing policy defines as its `top'
71 */
72static struct dccp_qpolicy_operations {
73	void		(*push)	(struct sock *sk, struct sk_buff *skb);
74	bool		(*full) (struct sock *sk);
75	struct sk_buff*	(*top)  (struct sock *sk);
76	__be32		params;
77
78} qpol_table[DCCPQ_POLICY_MAX] = {
79	[DCCPQ_POLICY_SIMPLE] = {
80		.push   = qpolicy_simple_push,
81		.full   = qpolicy_simple_full,
82		.top    = qpolicy_simple_top,
83		.params = 0,
84	},
85	[DCCPQ_POLICY_PRIO] = {
86		.push   = qpolicy_simple_push,
87		.full   = qpolicy_prio_full,
88		.top    = qpolicy_prio_best_skb,
89		.params = DCCP_SCM_PRIORITY,
90	},
91};
92
93/*
94 *	Externally visible interface
95 */
96void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
97{
98	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
99}
100
101bool dccp_qpolicy_full(struct sock *sk)
102{
103	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
104}
105
106void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
107{
108	if (skb != NULL) {
109		skb_unlink(skb, &sk->sk_write_queue);
110		kfree_skb(skb);
111	}
112}
113
114struct sk_buff *dccp_qpolicy_top(struct sock *sk)
115{
116	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
117}
118
119struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
120{
121	struct sk_buff *skb = dccp_qpolicy_top(sk);
122
123	if (skb != NULL) {
124		/* Clear any skb fields that we used internally */
125		skb->priority = 0;
126		skb_unlink(skb, &sk->sk_write_queue);
127	}
128	return skb;
129}
130
131bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param)
132{
133	/* check if exactly one bit is set */
134	if (!param || (param & (param - 1)))
135		return false;
136	return (qpol_table[dccp_sk(sk)->dccps_qpolicy].params & param) == param;
137}
138