GNU Linux-libre 4.19.211-gnu1
[releases.git] / net / sched / sch_plug.c
1 /*
2  * sch_plug.c Queue traffic until an explicit release command
3  *
4  *             This program is free software; you can redistribute it and/or
5  *             modify it under the terms of the GNU General Public License
6  *             as published by the Free Software Foundation; either version
7  *             2 of the License, or (at your option) any later version.
8  *
9  * There are two ways to use this qdisc:
10  * 1. A simple "instantaneous" plug/unplug operation, by issuing an alternating
11  *    sequence of TCQ_PLUG_BUFFER & TCQ_PLUG_RELEASE_INDEFINITE commands.
12  *
13  * 2. For network output buffering (a.k.a output commit) functionality.
14  *    Output commit property is commonly used by applications using checkpoint
15  *    based fault-tolerance to ensure that the checkpoint from which a system
16  *    is being restored is consistent w.r.t outside world.
17  *
18  *    Consider for e.g. Remus - a Virtual Machine checkpointing system,
19  *    wherein a VM is checkpointed, say every 50ms. The checkpoint is replicated
20  *    asynchronously to the backup host, while the VM continues executing the
21  *    next epoch speculatively.
22  *
23  *    The following is a typical sequence of output buffer operations:
24  *       1.At epoch i, start_buffer(i)
25  *       2. At end of epoch i (i.e. after 50ms):
26  *          2.1 Stop VM and take checkpoint(i).
27  *          2.2 start_buffer(i+1) and Resume VM
28  *       3. While speculatively executing epoch(i+1), asynchronously replicate
29  *          checkpoint(i) to backup host.
30  *       4. When checkpoint_ack(i) is received from backup, release_buffer(i)
31  *    Thus, this Qdisc would receive the following sequence of commands:
32  *       TCQ_PLUG_BUFFER (epoch i)
33  *       .. TCQ_PLUG_BUFFER (epoch i+1)
34  *       ....TCQ_PLUG_RELEASE_ONE (epoch i)
35  *       ......TCQ_PLUG_BUFFER (epoch i+2)
36  *       ........
37  */
38
39 #include <linux/module.h>
40 #include <linux/types.h>
41 #include <linux/kernel.h>
42 #include <linux/errno.h>
43 #include <linux/netdevice.h>
44 #include <linux/skbuff.h>
45 #include <net/pkt_sched.h>
46
47 /*
48  * State of the queue, when used for network output buffering:
49  *
50  *                 plug(i+1)            plug(i)          head
51  * ------------------+--------------------+---------------->
52  *                   |                    |
53  *                   |                    |
54  * pkts_current_epoch| pkts_last_epoch    |pkts_to_release
55  * ----------------->|<--------+--------->|+--------------->
56  *                   v                    v
57  *
58  */
59
60 struct plug_sched_data {
61         /* If true, the dequeue function releases all packets
62          * from head to end of the queue. The queue turns into
63          * a pass-through queue for newly arriving packets.
64          */
65         bool unplug_indefinite;
66
67         bool throttled;
68
69         /* Queue Limit in bytes */
70         u32 limit;
71
72         /* Number of packets (output) from the current speculatively
73          * executing epoch.
74          */
75         u32 pkts_current_epoch;
76
77         /* Number of packets corresponding to the recently finished
78          * epoch. These will be released when we receive a
79          * TCQ_PLUG_RELEASE_ONE command. This command is typically
80          * issued after committing a checkpoint at the target.
81          */
82         u32 pkts_last_epoch;
83
84         /*
85          * Number of packets from the head of the queue, that can
86          * be released (committed checkpoint).
87          */
88         u32 pkts_to_release;
89 };
90
91 static int plug_enqueue(struct sk_buff *skb, struct Qdisc *sch,
92                         struct sk_buff **to_free)
93 {
94         struct plug_sched_data *q = qdisc_priv(sch);
95
96         if (likely(sch->qstats.backlog + skb->len <= q->limit)) {
97                 if (!q->unplug_indefinite)
98                         q->pkts_current_epoch++;
99                 return qdisc_enqueue_tail(skb, sch);
100         }
101
102         return qdisc_drop(skb, sch, to_free);
103 }
104
105 static struct sk_buff *plug_dequeue(struct Qdisc *sch)
106 {
107         struct plug_sched_data *q = qdisc_priv(sch);
108
109         if (q->throttled)
110                 return NULL;
111
112         if (!q->unplug_indefinite) {
113                 if (!q->pkts_to_release) {
114                         /* No more packets to dequeue. Block the queue
115                          * and wait for the next release command.
116                          */
117                         q->throttled = true;
118                         return NULL;
119                 }
120                 q->pkts_to_release--;
121         }
122
123         return qdisc_dequeue_head(sch);
124 }
125
126 static int plug_init(struct Qdisc *sch, struct nlattr *opt,
127                      struct netlink_ext_ack *extack)
128 {
129         struct plug_sched_data *q = qdisc_priv(sch);
130
131         q->pkts_current_epoch = 0;
132         q->pkts_last_epoch = 0;
133         q->pkts_to_release = 0;
134         q->unplug_indefinite = false;
135
136         if (opt == NULL) {
137                 q->limit = qdisc_dev(sch)->tx_queue_len
138                            * psched_mtu(qdisc_dev(sch));
139         } else {
140                 struct tc_plug_qopt *ctl = nla_data(opt);
141
142                 if (nla_len(opt) < sizeof(*ctl))
143                         return -EINVAL;
144
145                 q->limit = ctl->limit;
146         }
147
148         q->throttled = true;
149         return 0;
150 }
151
152 /* Receives 4 types of messages:
153  * TCQ_PLUG_BUFFER: Inset a plug into the queue and
154  *  buffer any incoming packets
155  * TCQ_PLUG_RELEASE_ONE: Dequeue packets from queue head
156  *   to beginning of the next plug.
157  * TCQ_PLUG_RELEASE_INDEFINITE: Dequeue all packets from queue.
158  *   Stop buffering packets until the next TCQ_PLUG_BUFFER
159  *   command is received (just act as a pass-thru queue).
160  * TCQ_PLUG_LIMIT: Increase/decrease queue size
161  */
162 static int plug_change(struct Qdisc *sch, struct nlattr *opt,
163                        struct netlink_ext_ack *extack)
164 {
165         struct plug_sched_data *q = qdisc_priv(sch);
166         struct tc_plug_qopt *msg;
167
168         if (opt == NULL)
169                 return -EINVAL;
170
171         msg = nla_data(opt);
172         if (nla_len(opt) < sizeof(*msg))
173                 return -EINVAL;
174
175         switch (msg->action) {
176         case TCQ_PLUG_BUFFER:
177                 /* Save size of the current buffer */
178                 q->pkts_last_epoch = q->pkts_current_epoch;
179                 q->pkts_current_epoch = 0;
180                 if (q->unplug_indefinite)
181                         q->throttled = true;
182                 q->unplug_indefinite = false;
183                 break;
184         case TCQ_PLUG_RELEASE_ONE:
185                 /* Add packets from the last complete buffer to the
186                  * packets to be released set.
187                  */
188                 q->pkts_to_release += q->pkts_last_epoch;
189                 q->pkts_last_epoch = 0;
190                 q->throttled = false;
191                 netif_schedule_queue(sch->dev_queue);
192                 break;
193         case TCQ_PLUG_RELEASE_INDEFINITE:
194                 q->unplug_indefinite = true;
195                 q->pkts_to_release = 0;
196                 q->pkts_last_epoch = 0;
197                 q->pkts_current_epoch = 0;
198                 q->throttled = false;
199                 netif_schedule_queue(sch->dev_queue);
200                 break;
201         case TCQ_PLUG_LIMIT:
202                 /* Limit is supplied in bytes */
203                 q->limit = msg->limit;
204                 break;
205         default:
206                 return -EINVAL;
207         }
208
209         return 0;
210 }
211
212 static struct Qdisc_ops plug_qdisc_ops __read_mostly = {
213         .id          =       "plug",
214         .priv_size   =       sizeof(struct plug_sched_data),
215         .enqueue     =       plug_enqueue,
216         .dequeue     =       plug_dequeue,
217         .peek        =       qdisc_peek_head,
218         .init        =       plug_init,
219         .change      =       plug_change,
220         .reset       =       qdisc_reset_queue,
221         .owner       =       THIS_MODULE,
222 };
223
224 static int __init plug_module_init(void)
225 {
226         return register_qdisc(&plug_qdisc_ops);
227 }
228
229 static void __exit plug_module_exit(void)
230 {
231         unregister_qdisc(&plug_qdisc_ops);
232 }
233 module_init(plug_module_init)
234 module_exit(plug_module_exit)
235 MODULE_LICENSE("GPL");