baseroot: add flagfile to indicate we're in an initramfs

This is used by udev to deal with firmware requests for firmware that is
not available until the real root. It will also be used by systemd to
detect what to do, if that is ever used.

ref: http://www.spinics.net/lists/linux-wireless/msg94522.html

Signed-off-by: Tom Gundersen <teg@jklm.no>

functions

@@ -618,7 +618,7 @@ initialize_buildroot() {
     fi
 
     # base directory structure
-    install -dm755 "$workdir/root"/{new_root,proc,sys,dev,run,tmp,usr/{local,lib,bin}}
+    install -dm755 "$workdir/root"/{new_root,proc,sys,dev,run,tmp,etc,usr/{local,lib,bin}}
     ln -s "usr/lib" "$workdir/root/lib"
     ln -s "../lib"  "$workdir/root/usr/local/lib"
     ln -s "bin"     "$workdir/root/usr/sbin"
@@ -629,6 +629,9 @@ initialize_buildroot() {
     # kernel module dir
     install -dm755 "$workdir/root/usr/lib/modules/$kernver/kernel"
 
+    # indicate that this is an initramfs
+    >"$workdir/root/etc/initrd-release"
+
     printf '%s' "$workdir"
 }