xref: /linux/net/dccp/qpolicy.c (revision 2dbc0838bcf24ca59cabc3130cf3b1d6809cdcd4) 
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  */
15 static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
16 {
17 	skb_queue_tail(&sk->sk_write_queue, skb);
18 }
19 
20 static 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 
26 static 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  */
36 static 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 
46 static 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 
56 static 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  */
69 static 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  */
93 void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
94 {
95 	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
96 }
97 
98 bool dccp_qpolicy_full(struct sock *sk)
99 {
100 	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
101 }
102 
103 void 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 
111 struct sk_buff *dccp_qpolicy_top(struct sock *sk)
112 {
113 	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
114 }
115 
116 struct 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 
128 bool 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