udhcpc -x hostname:<name> not working on nommu

[Denys Vlasenko]

On Mon, May 8, 2017 at 3:41 AM, Ian Burns <Ian.Burns at rinstrum.com> wrote:
> Hi,
>
> As recommended, I've updated my udhcpc command line from "udhcpc -h <hostname> ..." to "udhcpc -x hostname:<hostname> ...".
> However when running as a daemon/background, the new "-x hostname" option ceases to send the hostname in the DHCP discover broadcast. I've confirmed this by looking at the network traffic. In foreground mode (--foreground), "-x hostname" works as expected.
>
> This issue may have come up previously: http://lists.busybox.net/pipermail/busybox/2012-July/078179.html but there was no resolution.
>
> I'm running busybox on a nommu platform, which compiles in some special case code in dhcpc.c
>
> Adding some debug prints before the call to bb_daemonize_or_rexec(), I get an argv of:
> "udhcpc", "--syslog", "--background", "-x", "hostname", "--interface", "eth0", NULL
>
> The "while (list_x) {" bit is modifying the hostname string with "*colon = ' ';" and the call to udhcp_str2optset(). The modified argv is then passed to bb_daemonize_or_rexec().
>
> My question is: Is there a way to know if the udhcpc instance is the original invocation, or the re-exec'd invocation?

There is a global bool variable, "re_execed".

> If there is a way to know, my proposed solution would be to conditionally run the "while (list_x) {" bit only once running as the re-exec'd udhcpc.

How about this:

--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -1365,6 +1365,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                /* now it looks similar to udhcpd's config file line:
                 * "optname optval", using the common routine: */
                udhcp_str2optset(optstr, &client_config.options);
+               if (colon)
+                       *colon = ':'; /* for NOMMU reexec */
        }

        if (udhcp_read_interface(client_config.interface,