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2874c5fd | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
c3059be1 SR |
2 | /* |
3 | * sch_plug.c Queue traffic until an explicit release command | |
4 | * | |
c3059be1 SR |
5 | * There are two ways to use this qdisc: |
6 | * 1. A simple "instantaneous" plug/unplug operation, by issuing an alternating | |
7 | * sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands. | |
8 | * | |
9 | * 2. For network output buffering (a.k.a output commit) functionality. | |
10 | * Output commit property is commonly used by applications using checkpoint | |
11 | * based fault-tolerance to ensure that the checkpoint from which a system | |
12 | * is being restored is consistent w.r.t outside world. | |
13 | * | |
14 | * Consider for e.g. Remus - a Virtual Machine checkpointing system, | |
15 | * wherein a VM is checkpointed, say every 50ms. The checkpoint is replicated | |
16 | * asynchronously to the backup host, while the VM continues executing the | |
17 | * next epoch speculatively. | |
18 | * | |
19 | * The following is a typical sequence of output buffer operations: | |
20 | * 1.At epoch i, start_buffer(i) | |
21 | * 2. At end of epoch i (i.e. after 50ms): | |
22 | * 2.1 Stop VM and take checkpoint(i). | |
23 | * 2.2 start_buffer(i+1) and Resume VM | |
24 | * 3. While speculatively executing epoch(i+1), asynchronously replicate | |
25 | * checkpoint(i) to backup host. | |
26 | * 4. When checkpoint_ack(i) is received from backup, release_buffer(i) | |
27 | * Thus, this Qdisc would receive the following sequence of commands: | |
28 | * TCQ_PLUG_BUFFER (epoch i) | |
29 | * .. TCQ_PLUG_BUFFER (epoch i+1) | |
30 | * ....TCQ_PLUG_RELEASE_ONE (epoch i) | |
31 | * ......TCQ_PLUG_BUFFER (epoch i+2) | |
32 | * ........ | |
33 | */ | |
34 | ||
35 | #include <linux/module.h> | |
36 | #include <linux/types.h> | |
37 | #include <linux/kernel.h> | |
38 | #include <linux/errno.h> | |
39 | #include <linux/netdevice.h> | |
40 | #include <linux/skbuff.h> | |
41 | #include <net/pkt_sched.h> | |
42 | ||
43 | /* | |
44 | * State of the queue, when used for network output buffering: | |
45 | * | |
46 | * plug(i+1) plug(i) head | |
47 | * ------------------+--------------------+----------------> | |
48 | * | | | |
49 | * | | | |
50 | * pkts_current_epoch| pkts_last_epoch |pkts_to_release | |
51 | * ----------------->|<--------+--------->|+---------------> | |
52 | * v v | |
53 | * | |
54 | */ | |
55 | ||
56 | struct plug_sched_data { | |
57 | /* If true, the dequeue function releases all packets | |
58 | * from head to end of the queue. The queue turns into | |
59 | * a pass-through queue for newly arriving packets. | |
60 | */ | |
61 | bool unplug_indefinite; | |
62 | ||
8fe6a79f ED |
63 | bool throttled; |
64 | ||
c3059be1 SR |
65 | /* Queue Limit in bytes */ |
66 | u32 limit; | |
67 | ||
68 | /* Number of packets (output) from the current speculatively | |
69 | * executing epoch. | |
70 | */ | |
71 | u32 pkts_current_epoch; | |
72 | ||
73 | /* Number of packets corresponding to the recently finished | |
74 | * epoch. These will be released when we receive a | |
75 | * TCQ_PLUG_RELEASE_ONE command. This command is typically | |
76 | * issued after committing a checkpoint at the target. | |
77 | */ | |
78 | u32 pkts_last_epoch; | |
79 | ||
80 | /* | |
81 | * Number of packets from the head of the queue, that can | |
82 | * be released (committed checkpoint). | |
83 | */ | |
84 | u32 pkts_to_release; | |
85 | }; | |
86 | ||
520ac30f ED |
87 | static int plug_enqueue(struct sk_buff *skb, struct Qdisc *sch, |
88 | struct sk_buff **to_free) | |
c3059be1 SR |
89 | { |
90 | struct plug_sched_data *q = qdisc_priv(sch); | |
91 | ||
92 | if (likely(sch->qstats.backlog + skb->len <= q->limit)) { | |
93 | if (!q->unplug_indefinite) | |
94 | q->pkts_current_epoch++; | |
95 | return qdisc_enqueue_tail(skb, sch); | |
96 | } | |
97 | ||
520ac30f | 98 | return qdisc_drop(skb, sch, to_free); |
c3059be1 SR |
99 | } |
100 | ||
101 | static struct sk_buff *plug_dequeue(struct Qdisc *sch) | |
102 | { | |
103 | struct plug_sched_data *q = qdisc_priv(sch); | |
104 | ||
8fe6a79f | 105 | if (q->throttled) |
c3059be1 SR |
106 | return NULL; |
107 | ||
108 | if (!q->unplug_indefinite) { | |
109 | if (!q->pkts_to_release) { | |
110 | /* No more packets to dequeue. Block the queue | |
111 | * and wait for the next release command. | |
112 | */ | |
8fe6a79f | 113 | q->throttled = true; |
c3059be1 SR |
114 | return NULL; |
115 | } | |
116 | q->pkts_to_release--; | |
117 | } | |
118 | ||
119 | return qdisc_dequeue_head(sch); | |
120 | } | |
121 | ||
e63d7dfd AA |
122 | static int plug_init(struct Qdisc *sch, struct nlattr *opt, |
123 | struct netlink_ext_ack *extack) | |
c3059be1 SR |
124 | { |
125 | struct plug_sched_data *q = qdisc_priv(sch); | |
126 | ||
127 | q->pkts_current_epoch = 0; | |
128 | q->pkts_last_epoch = 0; | |
129 | q->pkts_to_release = 0; | |
130 | q->unplug_indefinite = false; | |
131 | ||
132 | if (opt == NULL) { | |
348e3435 PS |
133 | q->limit = qdisc_dev(sch)->tx_queue_len |
134 | * psched_mtu(qdisc_dev(sch)); | |
c3059be1 SR |
135 | } else { |
136 | struct tc_plug_qopt *ctl = nla_data(opt); | |
137 | ||
138 | if (nla_len(opt) < sizeof(*ctl)) | |
139 | return -EINVAL; | |
140 | ||
141 | q->limit = ctl->limit; | |
142 | } | |
143 | ||
8fe6a79f | 144 | q->throttled = true; |
c3059be1 SR |
145 | return 0; |
146 | } | |
147 | ||
148 | /* Receives 4 types of messages: | |
149 | * TCQ_PLUG_BUFFER: Inset a plug into the queue and | |
150 | * buffer any incoming packets | |
151 | * TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head | |
152 | * to beginning of the next plug. | |
153 | * TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue. | |
154 | * Stop buffering packets until the next TCQ_PLUG_BUFFER | |
155 | * command is received (just act as a pass-thru queue). | |
156 | * TCQ_PLUG_LIMIT: Increase/decrease queue size | |
157 | */ | |
2030721c AA |
158 | static int plug_change(struct Qdisc *sch, struct nlattr *opt, |
159 | struct netlink_ext_ack *extack) | |
c3059be1 SR |
160 | { |
161 | struct plug_sched_data *q = qdisc_priv(sch); | |
162 | struct tc_plug_qopt *msg; | |
163 | ||
c3059be1 SR |
164 | msg = nla_data(opt); |
165 | if (nla_len(opt) < sizeof(*msg)) | |
166 | return -EINVAL; | |
167 | ||
168 | switch (msg->action) { | |
169 | case TCQ_PLUG_BUFFER: | |
170 | /* Save size of the current buffer */ | |
171 | q->pkts_last_epoch = q->pkts_current_epoch; | |
172 | q->pkts_current_epoch = 0; | |
173 | if (q->unplug_indefinite) | |
8fe6a79f | 174 | q->throttled = true; |
c3059be1 SR |
175 | q->unplug_indefinite = false; |
176 | break; | |
177 | case TCQ_PLUG_RELEASE_ONE: | |
178 | /* Add packets from the last complete buffer to the | |
179 | * packets to be released set. | |
180 | */ | |
181 | q->pkts_to_release += q->pkts_last_epoch; | |
182 | q->pkts_last_epoch = 0; | |
8fe6a79f | 183 | q->throttled = false; |
c3059be1 SR |
184 | netif_schedule_queue(sch->dev_queue); |
185 | break; | |
186 | case TCQ_PLUG_RELEASE_INDEFINITE: | |
187 | q->unplug_indefinite = true; | |
188 | q->pkts_to_release = 0; | |
189 | q->pkts_last_epoch = 0; | |
190 | q->pkts_current_epoch = 0; | |
8fe6a79f | 191 | q->throttled = false; |
c3059be1 SR |
192 | netif_schedule_queue(sch->dev_queue); |
193 | break; | |
194 | case TCQ_PLUG_LIMIT: | |
195 | /* Limit is supplied in bytes */ | |
196 | q->limit = msg->limit; | |
197 | break; | |
198 | default: | |
199 | return -EINVAL; | |
200 | } | |
201 | ||
202 | return 0; | |
203 | } | |
204 | ||
2132cf64 | 205 | static struct Qdisc_ops plug_qdisc_ops __read_mostly = { |
c3059be1 SR |
206 | .id = "plug", |
207 | .priv_size = sizeof(struct plug_sched_data), | |
208 | .enqueue = plug_enqueue, | |
209 | .dequeue = plug_dequeue, | |
8fc134fe | 210 | .peek = qdisc_peek_dequeued, |
c3059be1 SR |
211 | .init = plug_init, |
212 | .change = plug_change, | |
fe6bea7f | 213 | .reset = qdisc_reset_queue, |
c3059be1 SR |
214 | .owner = THIS_MODULE, |
215 | }; | |
241a94ab | 216 | MODULE_ALIAS_NET_SCH("plug"); |
c3059be1 SR |
217 | |
218 | static int __init plug_module_init(void) | |
219 | { | |
220 | return register_qdisc(&plug_qdisc_ops); | |
221 | } | |
222 | ||
223 | static void __exit plug_module_exit(void) | |
224 | { | |
225 | unregister_qdisc(&plug_qdisc_ops); | |
226 | } | |
227 | module_init(plug_module_init) | |
228 | module_exit(plug_module_exit) | |
229 | MODULE_LICENSE("GPL"); | |
f96118c5 | 230 | MODULE_DESCRIPTION("Qdisc to plug and unplug traffic via netlink control"); |