I tried to startup the wireless interface wlan0 on my router with the command "ifconfig wlan0 up", and it return "SIOCSIFFLAGS: Operation not permitted". Does anybody know what is SIOCSIFFLAGS? Of course I am using root mode to excute the command. How to debug the source code for this? Thanks for your help.

SIOCSIFFLAGS is an ioctl() call for your interface specifying some options/mode of operation for the card. For more information see:

Some synthesis :

This man page describes the sockets interface which is used to configure network devices.
They pass an ifreq structure

SIOCGIFFLAGS, SIOCSIFFLAGS
Get or set the active flag word of the device. ifr_flags contains a bit mask. [IFF_*]
Setting the active flag word is a privileged operation, but any process may read it.

SIOCGIFADDR, SIOCSIFADDR
Get or set the address of the device using ifr_addr. Setting the interface address is a privileged operation. For compatibility, only AF_INET addresses are accepted or returned.

SIOCGIFDSTADDR, SIOCSIFDSTADDR
Get or set the destination address of a point-to-point device using ifr_dstaddr.

SIOCGIFBRDADDR, SIOCSIFBRDADDR
Get or set the broadcast address for a device using ifr_brdaddr.

SIOCGIFNETMASK, SIOCSIFNETMASK
Get or set the network mask for a device using ifr_netmask.

SIOCGIFMETRIC, SIOCSIFMETRIC
Get or set the metric of the device using ifr_metric. This is currently not implemented; it sets ifr_metric to 0 if you attempt to read it and returns EOPNOTSUPP if you attempt to set it.
[...]

SEE ALSO
proc(5), capabilities(7), ip(7), rtnetlink(7)