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Openvswitch source code(1)

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In this post, I try to study the soruce code of openvswitch to learn how does the openvswitch kernel module works.

Preface

Openvswitch support two modes for user to config, user mode and kernel mode.
we will discuss the kernel mode in this article.

Software version: openvswitch v.20

SourceCode

datapath.c

This file is the main part of the kernel module and it will be compiled to the datapath.ko.

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module_init(dp_init);
module_exit(dp_cleanup);

MODULE_DESCRIPTION("Open vSwitch switching datapath");
MODULE_LICENSE("GPL");
MODULE_VERSION(VERSION);

The kernel will call its init function dp_init after the kernel module has been loaded.

The following is the work flow of the dp_init.

  • ovs_workqueues_init()
  • ovs_flow_init()
  • ovs_vport_init
  • register_pernet_device(&ovs_net_ops);
  • register_netdevice_notifier(&ovs_dp_device_notifier);
  • dp_register_genl();
  • schedule_delayed_work(&rehash_flow_wq, REHASH_FLOW_INTERVAL);

ovs_workqueues_init

workqueue.c

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static struct task_struct *workq_thread;
spin_lock_init(&wq_lock);
INIT_LIST_HEAD(&workq);
init_waitqueue_head(&more_work);

workq_thread = kthread_create(worker_thread, NULL, "ovs_workq");
if (IS_ERR(workq_thread))
return PTR_ERR(workq_thread);

wake_up_process(workq_thread);
  • Initail the worker queue.
  • Create a kernel thread and the handler is worker_thread
  • start the kernel thread by calling wake_up_process
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static int worker_thread(void *dummy)
{
        for (;;) {
                wait_event_interruptible(more_work,
                                (kthread_should_stop() || !list_empty(&workq)));

                if (kthread_should_stop())
                        break;

                run_workqueue();
        }

        return 0;
}
  • wait_event_interruptible make the thread hibernation and add into the queue more_work.
  • The thread will wake up until the condition “kthread_should_stop() || !list_empty(&workq))” is true.
  • It will call the run_workqueue after it wake up.
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static void run_workqueue(void)
{
        spin_lock_irq(&wq_lock);
        while (!list_empty(&workq)) {
                struct work_struct *work = list_entry(workq.next,
                                struct work_struct, entry);

                work_func_t f = work->func;
                list_del_init(workq.next);
                current_work = work;
                spin_unlock_irq(&wq_lock);

                work_clear_pending(work);
                f(work);

                BUG_ON(in_interrupt());
                spin_lock_irq(&wq_lock);
                current_work = NULL;
        }
        spin_unlock_irq(&wq_lock);
}
  • Get the work from the workq list and call the fucntion.

ovs_flow_init

flow.c

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/* Initializes the flow module.
 * Returns zero if successful or a negative error code. */
int ovs_flow_init(void)
{
        BUILD_BUG_ON(__alignof__(struct sw_flow_key) % __alignof__(long));
        BUILD_BUG_ON(sizeof(struct sw_flow_key) % sizeof(long));

        flow_cache = kmem_cache_create("sw_flow", sizeof(struct sw_flow), 0,
                                        0, NULL);
        if (flow_cache == NULL)
                return -ENOMEM;

        return 0;
}
  • use the kmem_cache_create to create a kernel cache with size sw_flow
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struct sw_flow {
        struct rcu_head rcu;
        struct hlist_node hash_node[2];
        u32 hash;

        struct sw_flow_key key;
        struct sw_flow_key unmasked_key;
        struct sw_flow_mask *mask;
        struct sw_flow_actions __rcu *sf_acts;

        spinlock_t lock;        /* Lock for values below. */
        unsigned long used;     /* Last used time (in jiffies). */
        u64 packet_count;       /* Number of packets matched. */
        u64 byte_count;         /* Number of bytes matched. */
        u8 tcp_flags;           /* Union of seen TCP flags. */
};
  • This struct store the info of each flow, including count, flow_key and flow_mask.

ovs_vport_init

vport.c”

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/**
 *      ovs_vport_init - initialize vport subsystem
 *
 * Called at module load time to initialize the vport subsystem.
 */
int ovs_vport_init(void)
{
        dev_table = kzalloc(VPORT_HASH_BUCKETS * sizeof(struct hlist_head),
                            GFP_KERNEL);
        if (!dev_table)
                return -ENOMEM;

        return 0;
}

  • Use kzalloc malloc the memory from kernel.

register_pernet_device(&ovs_net_ops)

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register_pernet_device(&ovs_net_ops);
  • Register a network device ovs_net_ops
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static struct pernet_operations ovs_net_ops = {
        .init = ovs_init_net,
        .exit = ovs_exit_net,
        .id   = &ovs_net_id,
        .size = sizeof(struct ovs_net),
};
  • ovs_net_ops inherent from pernet_operations, it should implement some function (init, exit)
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static int __net_init ovs_init_net(struct net *net)
{
        struct ovs_net *ovs_net = net_generic(net, ovs_net_id);

        INIT_LIST_HEAD(&ovs_net->dps);
        INIT_WORK(&ovs_net->dp_notify_work, ovs_dp_notify_wq);
        return 0;
}
  • Use net_generic get the pointer to ovs_net.
  • Use INIT_WORK to create a worker and set the function (dp_notify_work) as its work.
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struct ovs_net {
        struct list_head dps;
        struct vport_net vport_net;
        struct work_struct dp_notify_work;
};
  • need to study later.
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void ovs_dp_notify_wq(struct work_struct *work)
{
        struct ovs_net *ovs_net = container_of(work, struct ovs_net, dp_notify_work);
        struct datapath *dp;

        ovs_lock();
        list_for_each_entry(dp, &ovs_net->dps, list_node) {
                int i;

                for (i = 0; i < DP_VPORT_HASH_BUCKETS; i++) {
                        struct vport *vport;
                        struct hlist_node *n;

                        hlist_for_each_entry_safe(vport, n, &dp->ports[i], dp_hash_node) {
                                struct netdev_vport *netdev_vport;

                                if (vport->ops->type != OVS_VPORT_TYPE_NETDEV)
                                        continue;

                                netdev_vport = netdev_vport_priv(vport);
                                if (netdev_vport->dev->reg_state == NETREG_UNREGISTERED ||
                                    netdev_vport->dev->reg_state == NETREG_UNREGISTERING)
                                        dp_detach_port_notify(vport);
                        }
                }
        }
        ovs_unlock();
}
  • search datapathes and list all its vport.
  • Delete the vport if its status is UNREGISTERED of UNREGISTERING.

register_netdevice_notifier

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register_netdevice_notifier(&ovs_dp_device_notifier);
  • Register the network notification chain, it will call ovs_dp_device_notifier when event occur.
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struct notifier_block ovs_dp_device_notifier = {
        .notifier_call = dp_device_event
};
  • ovs_dp_device_notifier contains a function pointer which point to dp_device_event.
  • This function will be call when the notification has occur.
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static int dp_device_event(struct notifier_block *unused, unsigned long event,
                           void *ptr)
{
        struct ovs_net *ovs_net;
        struct net_device *dev = ptr;
        struct vport *vport = NULL;

        if (!ovs_is_internal_dev(dev))
                vport = ovs_netdev_get_vport(dev);

        if (!vport)
                return NOTIFY_DONE;

        if (event == NETDEV_UNREGISTER) {
                ovs_net = net_generic(dev_net(dev), ovs_net_id);
                queue_work(&ovs_net->dp_notify_work);
        }

        return NOTIFY_DONE;
}
  • Need to study.

dp_register_genl

datapath.c

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static int dp_register_genl(void)
{
        int n_registered;
        int err;
        int i;

        n_registered = 0;
        for (i = 0; i < ARRAY_SIZE(dp_genl_families); i++) {
                const struct genl_family_and_ops *f = &dp_genl_families[i];

                err = genl_register_family_with_ops(f->family, f->ops,
                                                    f->n_ops);
                if (err)
                        goto error;
                n_registered++;

                if (f->group) {
                        err = genl_register_mc_group(f->family, f->group);
                        if (err)
                                goto error;
                }
        }

        return 0;

error:
        dp_unregister_genl(n_registered);
        return err;
}
  • Register four types of gereric netlink (datapath, vport, flow, packet).
  • You can see the detail info in dp_genl_families
  • genl_register_family_with_ops : register a generic netlink family with ops.
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static const struct genl_family_and_ops dp_genl_families[] = {
        { &dp_datapath_genl_family,
          dp_datapath_genl_ops, ARRAY_SIZE(dp_datapath_genl_ops),
          &ovs_dp_datapath_multicast_group },
        { &dp_vport_genl_family,
          dp_vport_genl_ops, ARRAY_SIZE(dp_vport_genl_ops),
          &ovs_dp_vport_multicast_group },
        { &dp_flow_genl_family,
          dp_flow_genl_ops, ARRAY_SIZE(dp_flow_genl_ops),
          &ovs_dp_flow_multicast_group },
        { &dp_packet_genl_family,
          dp_packet_genl_ops, ARRAY_SIZE(dp_packet_genl_ops),
          NULL },
};
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struct genl_family_and_ops {
        struct genl_family *family;
        struct genl_ops *ops;
        int n_ops;
        struct genl_multicast_group *group;
};
  • A genl_family_and_ops contains a pointer to its family and a pointer to its operations.
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static struct genl_family dp_datapath_genl_family = {
        .id = GENL_ID_GENERATE,
        .hdrsize = sizeof(struct ovs_header),
        .name = OVS_DATAPATH_FAMILY,
        .version = OVS_DATAPATH_VERSION,
        .maxattr = OVS_DP_ATTR_MAX,
        .netnsok = true,
         SET_PARALLEL_OPS
};



static struct genl_ops dp_datapath_genl_ops[] = {
        { .cmd = OVS_DP_CMD_NEW,
          .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
          .policy = datapath_policy,
          .doit = ovs_dp_cmd_new
        },
        { .cmd = OVS_DP_CMD_DEL,
          .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
          .policy = datapath_policy,
          .doit = ovs_dp_cmd_del
        },
        { .cmd = OVS_DP_CMD_GET,
          .flags = 0,               /* OK for unprivileged users. */
          .policy = datapath_policy,
          .doit = ovs_dp_cmd_get,
          .dumpit = ovs_dp_cmd_dump
        },
        { .cmd = OVS_DP_CMD_SET,
          .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
          .policy = datapath_policy,
          .doit = ovs_dp_cmd_set,
        },
};
  • Take dp_datapath_genl_ops for example. when the event is OVS_DP_CMD_NEW it will call it function handler ovs_dp_cmd_new.

schedule_delayed_work

  • Need to study

other

  • pr_info is printk(KERN_INFO,pr_fmt(fmt), ##VA_ARGS)

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