sh: background dhcp at boot so the prompt is never blocked

dhcp's recv times out only after ~250*65536 pumps x3 retries, so
fork()+wait() left the screen stuck at 'dhcp: discovering' with no
prompt whenever no DHCP server answered (raw emulator, no bridge).
Fork without waiting: the prompt is immediate, the lease (or 'no
offer') lands a moment later, and the job is reaped by the main loop.

1 files changed, 6 insertions, 3 deletions

diff --git a/usr/sh.c b/usr/sh.c
index 3178894..a259b81 100644
--- a/usr/sh.c
+++ b/usr/sh.c
@@ -155,11 +155,14 @@ void main(void) {
     char *tok[16];
     char cwd[40];
     cwd[0] = '/'; cwd[1] = 0;
-    /* bring up networking first: run the DHCP client and wait for it to finish
-       (got a lease, or gave up). Only then drop to the prompt. */
+    /* bring up networking in the BACKGROUND: dhcp's recv blocks a long time when
+       no server answers, and wait()ing on it would leave the screen stuck at
+       "dhcp: discovering" with no prompt. Fork without waiting so the prompt is
+       immediate; the lease (or "no offer") lands a moment later and the job is
+       reaped by the loop below. */
     {
         unsigned char d = lookup("dhcp");
-        if (d != NOFD) { if (fork() == 0) exec(d); else wait(); }
+        if (d != NOFD && fork() == 0) exec(d);
     }
     for (;;) {
         unsigned char nt, i, pipepos, c, bg;