appliance/init: Allow daemon stack traces to be captured by gdb.

This fragment, not enabled by default, allows stack traces to be
captured and displayed by gdb in case the daemon crashes.

appliance/init

@@ -171,6 +171,19 @@ fi
 if test "$guestfs_network" = 1; then
     cmd="$cmd --network"
 fi
+if false; then
+    # To get a stack trace if the daemon crashes:
+    # (1) change this section to 'if true'
+    # (2) add 'gdb' to 'appliance/packagelist.in'
+    unset LD_PRELOAD
+    echo set pagination off  > /tmp/gdb-script
+    echo run                >> /tmp/gdb-script
+    echo info registers     >> /tmp/gdb-script
+    echo 'x/16i $pc'        >> /tmp/gdb-script
+    echo t a a bt           >> /tmp/gdb-script
+    echo quit               >> /tmp/gdb-script
+    cmd="gdb -batch -x /tmp/gdb-script --args $cmd"
+fi
 if ! test "$guestfs_rescue" = 1; then
     echo $cmd
     $cmd