initramfs: New modular initramfs for booting kernel from various media.

* Design principles:
* This initramfs just mounts roots and runs init on it, nothing else.
* Whenever possible, existing kernel parameters are used. When extended
  boot methods are provided, new parameters mimick/adhere to existing 
  conventions.
* System is modular/pluggable - each mount method is in own module with
  more or less well defined interface, it's possible to construct complete
  system with any combination of modules.
* Modules includes: initramfs-module-loop, initramfs-module-nfs, to boot
  from loop devices (including recursive loops) and NFS, correspondingly.

1 files changed, 65 insertions, 0 deletions

diff --git a/packages/initrdscripts/files/init.sh b/packages/initrdscripts/files/init.sh
new file mode 100644
index 0000000000..8c9803f21b
--- /dev/null
+++ b/packages/initrdscripts/files/init.sh
@@ -0,0 +1,65 @@
+#!/bin/sh
+
+MODULE_DIR=/initrd.d
+BOOT_ROOT=
+ROOT_DEVICE=/dev/null
+
+early_setup() {
+    mkdir /proc
+    mount -t proc proc /proc
+    mkdir /mnt
+
+    echo -n "creating device nodes: "
+    grep '^ *[0-9]' /proc/partitions | while read major minor blocks dev
+    do
+        if [ ! -e /dev/$dev ]; then
+            echo -n "$dev "
+            [ -e /dev/$dev ] || mknod /dev/$dev b $major $minor
+        fi
+    done
+    echo
+}
+
+read_args() {
+    CMDLINE=`cat /proc/cmdline`
+    for arg in $CMDLINE; do
+        optarg=`expr "x$arg" : 'x[^=]*=\(.*\)'`
+        case $arg in
+            root=*)
+                ROOT_DEVICE=$optarg ;;
+            rootdelay=*)
+                rootdelay=$optarg ;;
+        esac
+    done
+}
+
+load_modules() {
+    for module in $MODULE_DIR/*; do
+        source $module
+    done
+}
+
+boot_root() {
+    cd $BOOT_ROOT
+    exec switch_root -c /dev/console $BOOT_ROOT /sbin/init
+}
+
+boot_failed() {
+    echo "No valid root device was specified.  Please add root=/dev/something to"
+    echo "the kernel command-line and try again."
+    echo
+    exec sh
+}
+
+echo "Starting initramfs boot..."
+early_setup
+read_args
+
+if [ -n "$rootdelay" ]; then
+    echo "Waiting $rootdelay seconds for devices to settle..."
+    sleep $rootdelay
+fi
+
+load_modules
+[ -n "$BOOT_ROOT" ] && boot_root
+boot_failed