1. softgear@dcn.ssu.ac.kr

2. tc
Overview
User Space
include/linux/pkt_cls.h
include/linux/pkt_sched.h
net/netlink
struct sockaddr_nl
struct nlmsghdr
netlink socket
rtnetlink socket
net/core/rtnetlink.c
linux/include/rtnetlink.h
Kernel Space

3. Boot Time
__initfunc
pktsched_init
• declarations
• binding
net/core/dev.c
net/sched/sch_api.c

4. pktsched_init
struct rtnetlink_link *link_p;
if (link_p) {
link_p[RTM_NEWQDISC-RTM_BASE].doit = tc_ctl_qdisc;
link_p[RTM_DELQDISC-RTM_BASE].doit = tc_ctl_qdisc;
link_p[RTM_GETQDISC-RTM_BASE].doit = tc_ctl_qdisc;
link_p[RTM_GETQDISC-RTM_BASE].dumpit = tc_dump_qdisc;
link_p[RTM_NEWTCLASS-RTM_BASE].doit = tc_ctl_tclass;
link_p[RTM_DELTCLASS-RTM_BASE].doit = tc_ctl_tclass;
link_p[RTM_GETTCLASS-RTM_BASE].doit = tc_ctl_tclass;
link_p[RTM_GETTCLASS-RTM_BASE].dumpit = tc_dump_tclass;
}

5. User level Application
Create netlink socket
sendto
netlink_sendmsg
net/netlink/af_netlink.c
rtnetlink_rcv_msg
net/core/rtnetlink.c
call function in rtnetlink_link

6. nl_table
nl_table :
array of
INET socket linked list

7. rtnetlink_links
rtnetlink_links : array of
pointers to rtnetlink_link
rtnetlink_link : command

8. TC program
do_qdisc
tc_qdisc_modify
do_class
tc_qdisc_list
do_filter
usage

9. tc_qdisc_modify
allocate “req”
initialize it

10. tc_qdisc_modify (con’t)
rtnl_open : create ‘rtnetlink’ socket
family = AF_NETLINK
type = SOCK_RAW
protocol = NETLINK_ROUTE
setup and bind
local address, sockaddr_nl local
call “rtnl_talk”

11. rtnl_talk
allocate “msghdr msg”
call “sendmsg”
sys_sendmsg

12. sys_sendmsg
User space
req
msg
• sock_sendmsg
Kernel Space
Copy
req
msg
scm_cookie scm
call ‘scm_send’
call socket’s ‘sendmsg’ = netlink_ops
netlink_sendmsg

13. netlink_sendmsg
memcpy_from_iovec
msg
dstgroups
skbuff
msg
• netlink_broadcast
• netlink_unicast

14. netlink_unicast
socket’s protocol
pid
find ‘linked list’ in nl_tablel
add_wait_queue
skbuff
socket’s receive queue
call ‘data_ready’ = rtnetlink_rcv

15. rtnetlink_rcv
socket’s receive queue
invoke ‘rtnetlink_rcv_skb’
skbuff

16. rtnetlink_rcv_skb
skbuff
nlh
invoke ‘rtnetlink_rcv_msg’
passing ‘nlh’

17. rtnetlink_rcv_msg
invoke ‘doit’ in ‘rtnetlink_link’
In this case, doit = tc_modify_qdisc

18. middle summary
User Space
tc
nlmsghdr, tcmsg
netlink, rtnetlink
Kernel Space
rtnetlink_rcv
tc_get_qdisc
tc_modify_qdisc
tc_ctl_tfilter

19. tc_modify_qdisc
dev_get_by_index
index = tcm->tcm_ifindex
if qdisc parent is set,
call ‘qdisc_lookup’ : Find parent Q
call ‘qdisc_leaf’

20. tc_modify_qdisc (con’t)
if tcm->tcm_handle is not empty,
call ‘qdisc_lookup’ for band Q
fail
create_n_graft
graft

21. tc_modify_qdisc (con’t)
if tcm->tcm_handle is empty,
if q is empty
create_n_graft
else
create
graft

22. tc_modify_qdisc (con’t)
if (tcm->tcm_parent is not specified),
if (tcm->tcm->handle is not empty)
then call ‘qdisc_lookup’
call qdisc_change(q,tca)
‘qdisc_change’ call ‘prio_tune’

23. create_n_graft
dev, tcm->tcm_handle, tca, &err
qdisc_create

24. qdisc_create
find qdisc’s kind
using kind, get ‘Qdisc_ops’
allocate space for Q displine
call ‘skb_queue_head_init’
set up ‘enqueue’, ‘dequeue’
call ‘ops->init’
= prio_init
insert new Q into qdisc_list

25. graft
call ‘qdisc_graft’
connect ‘new’ to parent’s class
or dev
if parent Q displine is empty,
call ‘dev_graft_qdisc(dev,new)’
else call ‘get’ from class
call ‘qdisc_notify’

26. dev_graft_qdisc
dev_deactive
put old ‘qdisc_sleeping’ to ‘oqdisc’
if new Q is empty,
set new Q to noop_qdisc
then, set dev’s qdisc_sleeping to new Q,
dev->qdisc to noop_qdisc
Reactive device

27. prio_get
get minor class ID
prio_graft
using minor class ID as index which band

28. qdisc_chage
directly call ‘sch->ops->change’
chage = prio_tune

29. prio_tune
argument opt contains ‘bands’
outside band is set by ‘noop_qdisc’
update child Q by ‘prio2band array’
if Q == noop_qdisc
qdisc_create_dflt
qdisc_creat_dflt set up child Q
set up operator to ‘pfifo_qdisc_ops’