svn commit: r193199 - head/etc

John Baldwin jhb at
Tue Jun 2 19:45:46 UTC 2009

On Tuesday 02 June 2009 3:22:23 pm Doug Barton wrote:
> John Baldwin wrote:
> > I think more specifically, if you don't set 'ifconfig_<if>' to "DHCP", 
> > when you plug a <if> device in, nothing happens. 
> That's actually not correct, as devd will try to dhcp an interface as
> soon as it comes up.

That is completely wrong.  Checking the actual code would probably be helpful 
here.  From /etc/devd.conf:

# Try to start dhclient on Ethernet like interfaces when the link comes
# up.  Only devices that are configured to support DHCP will actually
# run it.  No link down rule exists because dhclient automaticly exits
# when the link goes down.
notify 0 {
        match "system"          "IFNET";
        match "type"            "LINK_UP";
        media-type              "ethernet";
        action "/etc/rc.d/dhclient start $subsystem";

Note the comment.  From /etc/rc.d/dhclient:


load_rc_config $name
load_rc_config network

if ! dhcpif $ifn; then
        return 1

run_rc_command "$1"

From /etc/network.subr:

# dhcpif if
#       Returns 0 if the interface is a DHCP interface and 1 otherwise.
        _tmpargs=`_ifconfig_getargs $1`
        for _arg in $_tmpargs; do
                case $_arg in
                        return 0
                        return 0
                        return 0
        return 1

Clearly if you do not have 'DHCP' set in your ifconfig_<if> variable, dhcpif 
will be false, and /etc/rc.d/dhclient will be a nop.

> > DHCP is opt-in, not 
> > opt-out.  The only reason one would want to limit network_interfaces is if 
> > you wanted to have an ifconfig_foo0 line in /etc/rc.conf but not have foo0 
> > configured automatically. 
> I've already said several times that I want to run through my own list
> of interfaces, configure the first one that comes up, and then stop.
> There is no support for that currently. Others have also chimed in
> with things that they do with the existing feature as well.

This is an interesting problem, though I think network_interfaces is a rather 
odd way of going about it.  Do you boot to single user and edit rc.conf all 
the time?  I don't see how else you are using network_interfaces to implement 
this.  I think a better solution to that problem would be to assign 
interfaces priority (if_priority_<if>="N" perhaps).  Also, note that 
the /etc/rc.d/defaultroute script does only hold up the boot until at least 
one interface gets a default route.  For the common wireless vs. wired case 
that works well, and even OS X will configure both wired and wireless 
interfaces if both work, it simply uses the priority to determine whose 
default route "wins".

John Baldwin

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