What I have:
I have a system with two interfaces (eth0 and eth1) which are bonded (bond0).

What I want:
I want to know when a link goes up or down and in or out of promiscuous mode without polling each interface all the time. I need this information for logging purposes - to write to a log file automatically.

What I have already done:
I know how to get the link up /down status by polling each interface continuously but, I don't want to do that. I tried some of the example NETLINK socket programs which listen and receive interface names. Using the flags I was able to distinguish between link up and link down since there are only two flag values I saw when plugging / unplugging the link. However, I don't know what they mean. If they are listed in /usr/include/net/if.h , then I am not able to interpret them properly.
When the interfaces are not bonded I noted the flags integer:
eth0 :4098 For link down
eth0 :4099 For link up
When the interfaces are bonded I noted the flags integer:
eth0 :6146 For link down
eth0 :6147 For link up
And bond0 has a different flags integer which shows up when I change the active slave without touching eth0 or eth1.
However I do not receive the status of the bonded interface when in enters or leaves promiscuous mode.


My questions:
1) How do I understand the flags correctly?
2) I am okay with sending a single request per interface once I have received the bond0 status. Using sendmsg I have not been able to do this. How do I accomplish this ?
3) Is there any easier way around this ?

ifi_flags is bit map, bit 0 indicate link status.

That makes sense. The if.h file says that 0x001 is for LINK UP.
This must be why the link up and link down flag values differ by one.
I'd still like to know about the other flags.
And I would really appreciate it if someone told me an easier way around this mess.

Since I've run out of time, I've decided to use the netlink program as it is. This is what I have :
I will be printing the individual interface up / down status identified by the flags. When the active slave changes within the bond, I receive a message with a different flag (70723) - this seems to be the standard message when any slave changes within the bond. When I receive this I check /sys/class/net/bond0/bonding/active_slave for the current active slave. Then I print this to the log file.

All flags of interface status is in if.h. The flags of bond slave and individual interface are different because thier attrubutes are different, such as master, slave and so on.