netdev

qdisc study part1: qdisc_base

###Qdisc_ops is the core of a Qdisc.
All kinds of the Qdisc_ops are linked in a list by qdisc_base.
The key item of different Qdisc_ops is id[IFNAMSIZ].

Note: the list is a Singly-linked list, not a common list of kernel.

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158 struct Qdisc_ops {
159         struct Qdisc_ops        *next;
160         const struct Qdisc_class_ops    *cl_ops;
161         char                    id[IFNAMSIZ];
162         int                     priv_size;
163
164         int                     (*enqueue)(struct sk_buff *, struct Qdisc *);
165         struct sk_buff *        (*dequeue)(struct Qdisc *);
166         struct sk_buff *        (*peek)(struct Qdisc *);
167         unsigned int            (*drop)(struct Qdisc *);
168
169         int                     (*init)(struct Qdisc *, struct nlattr *arg);
170         void                    (*reset)(struct Qdisc *);
171         void                    (*destroy)(struct Qdisc *);
172         int                     (*change)(struct Qdisc *, struct nlattr *arg);
173         void                    (*attach)(struct Qdisc *);
174
175         int                     (*dump)(struct Qdisc *, struct sk_buff *);
176         int                     (*dump_stats)(struct Qdisc *, struct gnet_dump *);
177
178         struct module           *owner;
179 };

qdisc_base

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134 /* The list of all installed queueing disciplines. */
135
136 static struct Qdisc_ops *qdisc_base;

the default Qdisc_ops is default_qdisc_ops.

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33 /* Qdisc to use by default */
34 const struct Qdisc_ops *default_qdisc_ops = &pfifo_fast_ops;
35 EXPORT_SYMBOL(default_qdisc_ops);
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526 struct Qdisc_ops pfifo_fast_ops __read_mostly = {
527         .id             =       "pfifo_fast",
528         .priv_size      =       sizeof(struct pfifo_fast_priv),
529         .enqueue        =       pfifo_fast_enqueue,
530         .dequeue        =       pfifo_fast_dequeue,
531         .peek           =       pfifo_fast_peek,
532         .init           =       pfifo_fast_init,
533         .reset          =       pfifo_fast_reset,
534         .dump           =       pfifo_fast_dump,
535         .owner          =       THIS_MODULE,
536 };

register_qdisc

The list is not a sorted list, it would be better with sorted list,
but these reg/unreg functions are rarely used.
do some basic check for the methods of Qdisc_ops,
and set some default values.

for example, method peek must be empty if method dequeue is empty.

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138 /* Register/uregister queueing discipline */
139
140 int register_qdisc(struct Qdisc_ops *qops)
141 {
142         struct Qdisc_ops *q, **qp;
143         int rc = -EEXIST;
144
145         write_lock(&qdisc_mod_lock);
146         for (qp = &qdisc_base; (q = *qp) != NULL; qp = &q->next)
147                 if (!strcmp(qops->id, q->id))
148                         goto out;
149
150         if (qops->enqueue == NULL)
151                 qops->enqueue = noop_qdisc_ops.enqueue;
152         if (qops->peek == NULL) {
153                 if (qops->dequeue == NULL)
154                         qops->peek = noop_qdisc_ops.peek;
155                 else
156                         goto out_einval;
157         }
158         if (qops->dequeue == NULL)
159                 qops->dequeue = noop_qdisc_ops.dequeue;
160
161         if (qops->cl_ops) {
162                 const struct Qdisc_class_ops *cops = qops->cl_ops;
163
164                 if (!(cops->get && cops->put && cops->walk && cops->leaf))
165                         goto out_einval;
166
167                 if (cops->tcf_chain && !(cops->bind_tcf && cops->unbind_tcf))
168                         goto out_einval;
169         }
170
171         qops->next = NULL;
172         *qp = qops;
173         rc = 0;
174 out:
175         write_unlock(&qdisc_mod_lock);
176         return rc;
177
178 out_einval:
179         rc = -EINVAL;
180         goto out;
181 }
182 EXPORT_SYMBOL(register_qdisc);

unregister_qdisc

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184 int unregister_qdisc(struct Qdisc_ops *qops)
185 {
186         struct Qdisc_ops *q, **qp;
187         int err = -ENOENT;
188
189         write_lock(&qdisc_mod_lock);
190         for (qp = &qdisc_base; (q = *qp) != NULL; qp = &q->next)
191                 if (q == qops)
192                         break;
193         if (q) {
194                 *qp = q->next;
195                 q->next = NULL;
196                 err = 0;
197         }
198         write_unlock(&qdisc_mod_lock);
199         return err;
200 }
201 EXPORT_SYMBOL(unregister_qdisc);

all Qdisc_ops

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junwei@localhost:~/git/linux$ grep register_qdisc net/ -Rw
net/sched/sch_sfb.c:    return register_qdisc(&sfb_qdisc_ops);
net/sched/sch_fq.c:     ret = register_qdisc(&fq_qdisc_ops);
net/sched/sch_choke.c:  return register_qdisc(&choke_qdisc_ops);
net/sched/sch_codel.c:  return register_qdisc(&codel_qdisc_ops);
net/sched/sch_qfq.c:    return register_qdisc(&qfq_qdisc_ops);
net/sched/sch_atm.c:    return register_qdisc(&atm_qdisc_ops);
net/sched/sch_multiq.c: return register_qdisc(&multiq_qdisc_ops);
net/sched/sch_cbq.c:    return register_qdisc(&cbq_qdisc_ops);
net/sched/sch_fq_codel.c:       return register_qdisc(&fq_codel_qdisc_ops);
net/sched/sch_dsmark.c: return register_qdisc(&dsmark_qdisc_ops);
net/sched/sch_hfsc.c:   return register_qdisc(&hfsc_qdisc_ops);
net/sched/sch_htb.c:    return register_qdisc(&htb_qdisc_ops);
net/sched/sch_api.c:int register_qdisc(struct Qdisc_ops *qops)
net/sched/sch_api.c:EXPORT_SYMBOL(register_qdisc);
net/sched/sch_api.c:    register_qdisc(&pfifo_fast_ops);
net/sched/sch_api.c:    register_qdisc(&pfifo_qdisc_ops);
net/sched/sch_api.c:    register_qdisc(&bfifo_qdisc_ops);
net/sched/sch_api.c:    register_qdisc(&pfifo_head_drop_qdisc_ops);
net/sched/sch_api.c:    register_qdisc(&mq_qdisc_ops);
net/sched/sch_blackhole.c:      return register_qdisc(&blackhole_qdisc_ops);
net/sched/sch_drr.c:    return register_qdisc(&drr_qdisc_ops);
net/sched/sch_netem.c:  return register_qdisc(&netem_qdisc_ops);
net/sched/sch_prio.c:   return register_qdisc(&prio_qdisc_ops);
net/sched/sch_gred.c:   return register_qdisc(&gred_qdisc_ops);
net/sched/sch_ingress.c:        return register_qdisc(&ingress_qdisc_ops);
net/sched/sch_mqprio.c: return register_qdisc(&mqprio_qdisc_ops);
net/sched/sch_sfq.c:    return register_qdisc(&sfq_qdisc_ops);
net/sched/sch_tbf.c:    return register_qdisc(&tbf_qdisc_ops);
net/sched/sch_red.c:    return register_qdisc(&red_qdisc_ops);
net/sched/sch_plug.c:   return register_qdisc(&plug_qdisc_ops);
net/sched/sch_teql.c:           err = register_qdisc(&master->qops);
junwei@localhost:~/git/linux$