##summary
IP4 route register a call back notify in IPv4 address.
When a address is added, fib_inetaddr_event will be called.

and then 4 route entry maybe added in fib_add_ifaddr

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SUMMARY

There is a struct in_device __rcu *ip_ptr under every net_device.
which stores all the IPv4 related information for this device.

Each IPv4 address is stored a struct in_ifaddr,
all the IPv4 address of a net device are stored into a list(netdev->ip_ptr->ifa_list).

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unregister_netdev is used to delete a net device. In fact, it equals:

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rtnl_lock();
rollback_registered_many( a temp list with a single net device);
list_add_tail(&dev->todo_list, &net_todo_list);
rtnl_unlock();

a temporary list stores a single net device, which is to be deleted.
net_todo_list stores all the net devices are being deleted.

The core function is rollback_registered_many, which efficiently deletes many devices in a list.
But here, in this case, one a single netdevice in the list.

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##summary

There is a struct rt_rq in struct rq. struct rt_rq is used to store all
the realtime task in current struct rq. which has a struct rt_prio_array active.

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summary

There are four sched_class,
stop_sched_class --> rt_sched_class --> fair_sched_class --> idle_sched_class

They are linked one by one staticly by struct sched_class->next by their defination.

Each sched_class has method pick_next_task, which is used to select
a perfect process to run from each sched_class‘s runqueue.

When we need schedule, the four pick_next_task will be called one by one.

As a optimization, most time there is no rt task in running state,
in this case we can directly call fair_sched_class.

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##summary:

1. struct rq is basic data structure.
2. there is a realtime process(es) and normal process(es) are stored in
   different sub-runqueue *_rq of rq?

   1 2	426 struct cfs_rq cfs; 427 struct rt_rq rt;

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Isolcpus

kthread has wrong affinity when use isolcpus in bootline

when boot kernel with isolcpus in grub command lines, only init thread has expected affinity, which exclude the isolated cpus.

while the kthreads affinity still includes isolated cpus.

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JUN 27TH, 2013 | COMMENTS
How to create a kernel thread

create a kthread by kthread_create

kthread_create(threadfn, data, namefmt, arg...)

example: file drivers/char/apm-emulation.c

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651 kapmd_tsk = kthread_create(kapmd, NULL, "kapmd");

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git send-email --annotate  --subject-prefix="PATCH v2 net-next" \
  --in-reply-to=The_previous_email_message_id_to_be_replied \
  --smtp-debug --to MAINTENACE_person_email --cc CCLIST HEAD^^

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summary

promisc is one bit of struct net_device’s flag, which is used to indicate if a device is in promisc status.

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30 /* Standard interface flags (netdevice->flags). */
31 #define IFF_UP          0x1             /* interface is up              */
32 #define IFF_BROADCAST   0x2             /* broadcast address valid      */
33 #define IFF_DEBUG       0x4             /* turn on debugging            */
34 #define IFF_LOOPBACK    0x8             /* is a loopback net            */
35 #define IFF_POINTOPOINT 0x10            /* interface is has p-p link    */
36 #define IFF_NOTRAILERS  0x20            /* avoid use of trailers        */
37 #define IFF_RUNNING     0x40            /* interface RFC2863 OPER_UP    */
38 #define IFF_NOARP       0x80            /* no ARP protocol              */
39 #define IFF_PROMISC     0x100           /* receive all packets          */
40 #define IFF_ALLMULTI    0x200           /* receive all multicast packets*/
...

There are two kinds of operataion, could cause a NIC enter/leave promisc status.

1. ip command
   run mutli on command, just need one off to recover.

   1 2	ip link set dev eth0 promisc on ip link set dev eth0 promisc off

2. tcpdump command
   When tcpdump starts, it let dev to promisc,
   and just before exit, tcpdump let dev left promisc.
   All these is done by call kernel api dev_set_promiscuity.

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