xref: /kernel/linux/linux-5.10/net/dccp/qpolicy.c (revision 8c2ecf20) 
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  net/dccp/qpolicy.c
4 *
5 *  Policy-based packet dequeueing interface for DCCP.
6 *
7 *  Copyright (c) 2008 Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
8 */
9#include "dccp.h"
10
11/*
12 *	Simple Dequeueing Policy:
13 *	If tx_qlen is different from 0, enqueue up to tx_qlen elements.
14 */
15static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
16{
17	skb_queue_tail(&sk->sk_write_queue, skb);
18}
19
20static bool qpolicy_simple_full(struct sock *sk)
21{
22	return dccp_sk(sk)->dccps_tx_qlen &&
23	       sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
24}
25
26static struct sk_buff *qpolicy_simple_top(struct sock *sk)
27{
28	return skb_peek(&sk->sk_write_queue);
29}
30
31/*
32 *	Priority-based Dequeueing Policy:
33 *	If tx_qlen is different from 0 and the queue has reached its upper bound
34 *	of tx_qlen elements, replace older packets lowest-priority-first.
35 */
36static struct sk_buff *qpolicy_prio_best_skb(struct sock *sk)
37{
38	struct sk_buff *skb, *best = NULL;
39
40	skb_queue_walk(&sk->sk_write_queue, skb)
41		if (best == NULL || skb->priority > best->priority)
42			best = skb;
43	return best;
44}
45
46static struct sk_buff *qpolicy_prio_worst_skb(struct sock *sk)
47{
48	struct sk_buff *skb, *worst = NULL;
49
50	skb_queue_walk(&sk->sk_write_queue, skb)
51		if (worst == NULL || skb->priority < worst->priority)
52			worst = skb;
53	return worst;
54}
55
56static bool qpolicy_prio_full(struct sock *sk)
57{
58	if (qpolicy_simple_full(sk))
59		dccp_qpolicy_drop(sk, qpolicy_prio_worst_skb(sk));
60	return false;
61}
62
63/**
64 * struct dccp_qpolicy_operations  -  TX Packet Dequeueing Interface
65 * @push: add a new @skb to the write queue
66 * @full: indicates that no more packets will be admitted
67 * @top:  peeks at whatever the queueing policy defines as its `top'
68 */
69static struct dccp_qpolicy_operations {
70	void		(*push)	(struct sock *sk, struct sk_buff *skb);
71	bool		(*full) (struct sock *sk);
72	struct sk_buff*	(*top)  (struct sock *sk);
73	__be32		params;
74
75} qpol_table[DCCPQ_POLICY_MAX] = {
76	[DCCPQ_POLICY_SIMPLE] = {
77		.push   = qpolicy_simple_push,
78		.full   = qpolicy_simple_full,
79		.top    = qpolicy_simple_top,
80		.params = 0,
81	},
82	[DCCPQ_POLICY_PRIO] = {
83		.push   = qpolicy_simple_push,
84		.full   = qpolicy_prio_full,
85		.top    = qpolicy_prio_best_skb,
86		.params = DCCP_SCM_PRIORITY,
87	},
88};
89
90/*
91 *	Externally visible interface
92 */
93void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
94{
95	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
96}
97
98bool dccp_qpolicy_full(struct sock *sk)
99{
100	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
101}
102
103void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
104{
105	if (skb != NULL) {
106		skb_unlink(skb, &sk->sk_write_queue);
107		kfree_skb(skb);
108	}
109}
110
111struct sk_buff *dccp_qpolicy_top(struct sock *sk)
112{
113	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
114}
115
116struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
117{
118	struct sk_buff *skb = dccp_qpolicy_top(sk);
119
120	if (skb != NULL) {
121		/* Clear any skb fields that we used internally */
122		skb->priority = 0;
123		skb_unlink(skb, &sk->sk_write_queue);
124	}
125	return skb;
126}
127
128bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param)
129{
130	/* check if exactly one bit is set */
131	if (!param || (param & (param - 1)))
132		return false;
133	return (qpol_table[dccp_sk(sk)->dccps_qpolicy].params & param) == param;
134}
135