tinyramfs/generate

#!/bin/sh
#
# tiny initramfs generation tool

# debugging
set -x

# check root
if [ "$(id -u)" != 0 ]; then
    echo "must be run as root!"
    exit 1
fi

# check files
[ -f ./config ] && . ./config || ( echo "config doesn't exists";exit 1 )
[ -x ./busybox ] && ldd ./busybox | grep -q "not a dynamic executable" || ( echo "busybox doesn't exists or dynamically linked. please download or/and build static busybox";exit 1 )
[ -f ./init ] || ( echo "init doesn't exists";exit 1 )

# variables
tmpdir="$(mktemp -d /tmp/initramfs.XXXXXXXX)"
kernel="$(uname -r)"
moddir="/lib/modules"

# structure
for d in bin dev etc usr/lib usr/bin mnt/root proc root sys; do
    mkdir -p "$tmpdir/$d"
done

# make libraries and binaries happy
ln -rs "$tmpdir/usr/lib" "$tmpdir/lib"
ln -rs "$tmpdir/usr/lib" "$tmpdir/lib64"
ln -rs "$tmpdir/usr/lib" "$tmpdir/lib32"
ln -rs "$tmpdir/usr/bin" "$tmpdir/bin"
ln -rs "$tmpdir/usr/bin" "$tmpdir/sbin"

# TODO parse fstab | crypttab
#while [ "$use_fstab" -eq 1 ] && read fs dir type opts; do thing; done < /etc/fstab

# TODO rewrite drivers installing | handle $drivers config var
# install drivers
find "$moddir/$kernel/kernel/drivers/virtio" "$moddir/$kernel/kernel/arch" "$moddir/$kernel/kernel/crypto" "$moddir/$kernel/kernel/fs" "$moddir/$kernel/kernel/lib" "$moddir/$kernel/kernel/drivers/block" "$moddir/$kernel/kernel/drivers/ata" "$moddir/$kernel/kernel/drivers/md" "$moddir/$kernel/kernel/drivers/scsi" "$moddir/$kernel/kernel/drivers/usb/storage" "$moddir/$kernel/kernel/drivers/usb/host" -type f -exec cp --parents "{}" "$tmpdir" ";"
cp "$moddir/$kernel/modules.softdep" "$moddir/$kernel/modules.builtin" "$moddir/$kernel/modules.order" "$tmpdir/$moddir/$kernel"

# create modules.* files
depmod -b "$tmpdir" "$kernel"

# install binaries
for b in $(echo $binaries); do
    cp "$(which $b)" "$tmpdir/usr/bin/$b" && chmod +x "$tmpdir/usr/bin/$b"
    # check statically linking
    ldd "$(which $b)" >/dev/null || continue

    # handle .so symlinks for dymanically linked binaries
    for l in $(ldd "$(which $b)" | sed -nre 's,.* (/.*lib.*/.*.so.*) .*,\1,p' -e 's,.*(/lib.*/ld.*.so.*) .*,\1,p'); do
	if [ -h "$l" ]; then
	    # regular
	    cp -n --parents "$(readlink -f $l)" "$tmpdir"
	    # symlink
	    cp -n -a --parents "$l" "$tmpdir"
	else
	    cp -n --parents "$(readlink -f $l)" "$tmpdir"
	fi
    done
done

# install files
cp ./init "$tmpdir/init" && chmod +x "$tmpdir/init"
cp ./busybox "$tmpdir/bin/busybox" && chmod +x "$tmpdir/bin/busybox"

# strip binaries and libraries
# uncomment this if your initramfs are huge
#find "$tmpdir" -type f -executable -exec strip -s "{}" ";"

# initialize config
cat <<EOF > "$tmpdir/config"
root="$root"
rootfstype="$rootfstype"
rootflags="$rootflags"
drivers="$drivers"
#use_lvm="$use_lvm"
#lvm_discard="$lvm_discard"
#use_luks="$use_luks"
#luks_header="$luks_header"
#luks_keyfile="$luks_keyfile"
#luks_discard="$luks_discard"
EOF

# packing
if ! ( cd "$tmpdir" && find . | cpio --create --verbose --format=newc | gzip --best ) > "./initramfs-$kernel.img.gz"; then
    echo "failed"
    exit 1
fi

rm -rf "$tmpdir"

echo "done! check out initramfs-$kernel.img.gz"