[9fans] Small patch to tftpd; command line announce strings.

[Dan Cross <cross@math.psu.edu>]

My new setup (which is still not on the Internet just yet, and probably
won't be for a few weeks at this point) is a little...weird.  I have
two interfaces bound to a single IP stack, one exposed to the net, one
not.  For a variety of reasons, this is more convenient than using
multiple stacks (in particular, I want to run services on both
interfaces, and listen doesn't seem to have a ``-x'' option, I don't
want to start everything twice, and I want to try and play some routing
tricks later where the internal interface will also answer requests
[from internal clients] for the external interface).  I'm running a
DHCP and tftpd server for internal clients, but I don't want any fool
with a tftp client to start downloading kernels from me.  DHCP I don't
care about since ip/dhcpd only answers for clients it knows about by
default, and the immediate subnet is pretty trustworthy.  The upshot
of all this is that I modified tftpd to add a ``-A'' option which takes
an announce string, so one can specify an interface to announce on.
E.g., ``ip/tftpd -A 'udp!192.168.1.4!69' '' sort of thing.  A diff in
diff -e format is below.  Are there any objections for adding this to
the distribution?

	- Dan C.

term% diff -e /n/sources/plan9/sys/src/cmd/ip/tftpd.c tftpd.c
102c
	sprint(buf, "%s/%s", net, a);
.
60a
	case 'A':
		a = ARGF();
		break;
.
58a
	a = "udp!*!69";
.
57c
	char *p, *a;
.
term%