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   */
qpolicy_simple_push(struct sock * sk,struct sk_buff * skb)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  
qpolicy_simple_full(struct sock * sk)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  
qpolicy_simple_top(struct sock * sk)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   */
qpolicy_prio_best_skb(struct sock * sk)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  
qpolicy_prio_worst_skb(struct sock * sk)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  
qpolicy_prio_full(struct sock * sk)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   * @params: parameter passed to policy operation
69   */
70  struct dccp_qpolicy_operations {
71  	void		(*push)	(struct sock *sk, struct sk_buff *skb);
72  	bool		(*full) (struct sock *sk);
73  	struct sk_buff*	(*top)  (struct sock *sk);
74  	__be32		params;
75  };
76  
77  static struct dccp_qpolicy_operations qpol_table[DCCPQ_POLICY_MAX] = {
78  	[DCCPQ_POLICY_SIMPLE] = {
79  		.push   = qpolicy_simple_push,
80  		.full   = qpolicy_simple_full,
81  		.top    = qpolicy_simple_top,
82  		.params = 0,
83  	},
84  	[DCCPQ_POLICY_PRIO] = {
85  		.push   = qpolicy_simple_push,
86  		.full   = qpolicy_prio_full,
87  		.top    = qpolicy_prio_best_skb,
88  		.params = DCCP_SCM_PRIORITY,
89  	},
90  };
91  
92  /*
93   *	Externally visible interface
94   */
dccp_qpolicy_push(struct sock * sk,struct sk_buff * skb)95  void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
96  {
97  	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
98  }
99  
dccp_qpolicy_full(struct sock * sk)100  bool dccp_qpolicy_full(struct sock *sk)
101  {
102  	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
103  }
104  
dccp_qpolicy_drop(struct sock * sk,struct sk_buff * skb)105  void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
106  {
107  	if (skb != NULL) {
108  		skb_unlink(skb, &sk->sk_write_queue);
109  		kfree_skb(skb);
110  	}
111  }
112  
dccp_qpolicy_top(struct sock * sk)113  struct sk_buff *dccp_qpolicy_top(struct sock *sk)
114  {
115  	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
116  }
117  
dccp_qpolicy_pop(struct sock * sk)118  struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
119  {
120  	struct sk_buff *skb = dccp_qpolicy_top(sk);
121  
122  	if (skb != NULL) {
123  		/* Clear any skb fields that we used internally */
124  		skb->priority = 0;
125  		skb_unlink(skb, &sk->sk_write_queue);
126  	}
127  	return skb;
128  }
129  
dccp_qpolicy_param_ok(struct sock * sk,__be32 param)130  bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param)
131  {
132  	/* check if exactly one bit is set */
133  	if (!param || (param & (param - 1)))
134  		return false;
135  	return (qpol_table[dccp_sk(sk)->dccps_qpolicy].params & param) == param;
136  }
137