Subject: Re: pkgsrc/wakeup with multiple interfaces
To: None <email@example.com>
From: John F <firstname.lastname@example.org>
Date: 12/13/2005 00:35:46
> On Mon, Dec 12, 2005, David Young wrote:
> Reading your patch, it looks like it gets the interface-specific source
> using select_if, and then overwrites it with INADDR_ANY before calling
> bind(2). Maybe you are on the right track, you just have a bug?
I was getting embarrassed for a second there, but no, I believe it is not
a bug. There are two sockaddr_in structs, named client and server.
select_if is called on server and then s_addr = INADDR_ANY is declared on
client, or vice versa for try #2.
It may be a bit confusing to read the second patch I sent, since it was
based off the first patch. I was aiming for a smaller patch - I wanted to
avoid resending the entire select_if function a second time.
> For a multicast UDP socket, I specify the outbound interface by its
> ifindex, like this:
It looks like the fourth argument, &addr, is the key here.
Its a very interesting bit of code. The man page just talks about the
SOL_SOCKET level and you're working at the IP level instead of the higher
level socket level. I see that this is documented in the 'ip' man page -
which I haven't looked at carefully yet. (There is so much documentation
to read..) getsockopt says it uses &addr to access an option value, and
you've run htonl on that. So, ifindex has got to be a real IP address..
Well, I'll play with it and see what it does for me.
All of the above said...
net/wol... Excellent!! And, I wasn't aware that magic packets had a
security feature?! I don't believe my Mac OS X client computer implements
that.. (I haven't checked, could be wrong, but iirc the gui simply
provides a checkbox for en/disabling wake on lan.)
I think I'll continue to hack on the wakeup program a bit further, as at
this point its a good/simple way for me to tool around with socket
programming in C, but had I known about 'wol' earlier I would have never
begun toying with 'wakeup'. And, if I can't figure out how to do what I
set out to do with 'wakeup' and just want to be done with it, or I just
want to see a completely different approach to solving the problem, I will
be using wol. What a terrific suggestion!
Thank you David and thank you Daniel.