制作initrd(2):update-initramfs和mkinitramfs脚本分析

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制作initrd(2):update-initramfs和mkinitramfs脚本分析

2015-11-26 01:10 本站整理 浏览(90)

制作initrd(2):update-initramfs和mkinitramfs脚本分析，有需要的朋友可以参考下。

 

前一篇文章<制作initrd(1):向initrd内部更新驱动模块>提到更新initrd.img镜像时需要运行update-initramfs命令。

起初以为是二进制文件，网上胡乱搜索一通发现update-initramfs和mkinitramfs两个命令同为脚本文件，既然是shell脚本那必须得分析内容并备忘。

 

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root@ubuntu:~# file `which update-initramfs`
/usr/sbin/update-initramfs: POSIX shell script, ASCII text executable
root@ubuntu:~# file `which mkinitramfs`
/usr/sbin/mkinitramfs: POSIX shell script, ASCII text executable

 

总的来说，编译内核的最后一步执行make install时会调用update-initramfs，update-initramfs继而调用mkinitramfs生成initrd.img。因此，mkinitramfs是核心脚本，他的作用是啥？如果你有手工做过initrd.img的经历，一定记得这是一个往临时initrd目录copy文件的繁琐过程，mkinitramfs则用脚本替代了手工操作(真伟大，还把人逼失业了！)：

1).在临时initrd目录下构建FHS规定的文件系统;

2).按/etc/initramfs-tools/module和/etc/modules文件的配置，往lib/modules/目录拷贝模块，同时生成模块依赖文件modules.dep，以后内核启动后会从initramfs中(initrd.img被解压到内存中)按模块依赖关系modprobe模块;

3).拷贝/etc/initramfs-tools/scripts和/usr/share/initramfs-tools/scripts下的配置文件到conf/目录下,以后内核启动，创建第一个进程init(initrd.img根目录下init.sh文件)会从conf/*读取配置，按一定的顺序加载模块/执行程序;

4).模块的加载离不开modprobe工具集，因此需要拷贝modprobe工具集及其他工具到initrd目录结构下，同时解决这些工具的依赖关系(依赖的so文件的路径);

5).所有步骤完成，调用cpio和gzip工具打包压缩临时initrd目录结构。

上面是mkinitramfs整体流程的概括，下面直接贴注释后脚本，如注释有误请在留言栏告诉我，谢谢~

 

首先是update-initramfs脚本，仅注释了执行update-initramfs -u更新initrd.img时的脚本执行流。脚本的开始定义了一些变量，然后跳去执行L400+之后的while getopts... do--按命令参数设置不同的运行模式。之后，按运行模式，进入不同的函数，以执行update-initramfs -u为例，进入update函数。

 

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#!/bin/sh
 
STATEDIR=/var/lib/initramfs-tools
BOOTDIR=/boot
CONF=/etc/initramfs-tools/update-initramfs.conf
USETRIGGERS=true
mode=""
version=""
update_initramfs=yes
backup_initramfs=no
 
set -e
#CONF存在且可读 则source ${CONF}中的设置 即source <span style="font-family: Arial, Helvetica, sans-serif;">/etc/initramfs-tools/update-initramfs.conf文件里的变量</span>
 
[ -r ${CONF} ] && . ${CONF}
 
case "$DPKG_MAINTSCRIPT_PACKAGE" in
linux-image-*)
    #INITRAMFS_TOOLS_KERNEL_HOOK 长度为0
    if [ -z "$INITRAMFS_TOOLS_KERNEL_HOOK" ]; then
        # kernel maintainer script called us directly; ignore
        # it and let the hook script handle it instead
        echo "update-initramfs: deferring update (hook will be called later)"
        exit 0
    fi
    ;;
?*)
    if     $USETRIGGERS                     \ #USETRIGGERS=true
        && [ $# = 1 ]                       \ #参数数量==1
        && [ x"$1" = x-u ]                  \ #第一个参数是-u
        && dpkg-trigger --check-supported 2>/dev/null
    then
        if dpkg-trigger --no-await update-initramfs; then
            echo "update-initramfs: deferring update (trigger activated)"
            exit 0
        fi
    fi
    ;;
esac
#开始定义一些函数 先搜索getopts，定位到那继续
usage()
{
    if [ -n "${1:-}" ]; then
        printf "${*}\n\n" >&2
    fi
    cat >&2 << EOF
Usage: ${0} [OPTION]...
 
Options:
 -k [version]   Specify kernel version or 'all'
 -c     Create a new initramfs
 -u     Update an existing initramfs
 -d     Remove an existing initramfs
 -t     Take over a custom initramfs with this one
 -b     Set alternate boot directory
 -v     Be verbose
 -h     This message
 
EOF
    exit 1
}
 
# chroot check
chrooted()
{
    # borrowed from udev's postinst
    if [ "$(stat -c %d/%i /)" = "$(stat -Lc %d/%i /proc/1/root 2>/dev/null)" ]; then
        # the devicenumber/inode pair of / is the same as that of
        # /sbin/init's root, so we're *not* in a chroot and hence
        # return false.
        return 1
    fi
return 0
}
 
mild_panic()
{
    if [ -n "${1:-}" ]; then
        printf "${*}\n" >&2
    fi
    exit 0
}
 
panic()
{
    if [ -n "${1:-}" ]; then
        printf "${*}\n" >&2
    fi
    exit 1
}
 
verbose()
{
    if [ "${verbose}" = 1 ]; then
        printf "${*}\n"
    fi
}
 
version_exists()
{
    [ -e "${STATEDIR}/${1}" ] && [ -e "${initramfs}" ]
    return $?
}
 
set_initramfs()
{
    initramfs="${BOOTDIR}/initrd.img-${version}"
}
 
 
# backup initramfs while running
backup_initramfs()
{
    [ ! -r "${initramfs}" ] && return 0
    initramfs_bak="${initramfs}.dpkg-bak"
    [ -r "${initramfs_bak}" ] && rm -f "${initramfs_bak}"
    ln -f "${initramfs}" "${initramfs_bak}" \
        || cp -a "${initramfs}" "${initramfs_bak}"
    verbose "Keeping ${initramfs_bak}"
}
 
# keep booted initramfs
backup_booted_initramfs()
{
    initramfs_bak="${initramfs}.dpkg-bak"
 
    # first time run thus no backup
    [ ! -r "${initramfs_bak}" ] && return 0
 
    # chroot with no /proc
    [ ! -r /proc/uptime ] && rm -f "${initramfs_bak}" && return 0
 
    # no kept backup wanted
    [ "${backup_initramfs}" = "no" ] && rm -f "${initramfs_bak}" && return 0
 
    # no backup yet
    if [ ! -r "${initramfs}.bak" ]; then
        mv -f ${initramfs_bak} "${initramfs}.bak"
        verbose "Backup ${initramfs}.bak"
        return 0
    fi
 
    # keep booted initramfs
    boot_initramfs=
    uptime_days=$(awk '{printf "%d", $1 / 3600 / 24}' /proc/uptime)
    if [ -n "$uptime_days" ]; then
        boot_initramfs=$(find "${initramfs}.bak" -mtime +${uptime_days})
    fi
    if [ -n "${boot_initramfs}" ]; then
        mv -f "${initramfs_bak}" "${initramfs}.bak"
        verbose "Backup ${initramfs}.bak"
        return 0
    fi
    verbose "Removing current backup ${initramfs_bak}"
    rm -f ${initramfs_bak}
}
 
# nuke generated copy
remove_initramfs_bak()
{
    [ -z "${initramfs_bak:-}" ] && return 0
    rm -f "${initramfs_bak}"
    verbose "Removing ${initramfs_bak}"
}
 
 
generate_initramfs()
{
    echo "update-initramfs: Generating ${initramfs}"
    OPTS="-o"
    if [ "${verbose}" = 1 ]; then
        OPTS="-v ${OPTS}"
    fi
    #if分支其实做这两件事
    #mkinitramfs -o /boot/initrd.img-`uname -r`.new  ${version}
    #mv /boot/initrd.img-`uname -r`.new /boot/initrd.img-`uname -r`
     
    if mkinitramfs ${OPTS} "${initramfs}.new" "${version}"; then
        mv -f "${initramfs}.new" "${initramfs}"
        set_sha1
    else
        mkinitramfs_return="$?"
        remove_initramfs_bak
        rm -f "${initramfs}.new"
        if [ "$mkinitramfs_return" = "2" ]; then
            # minversion wasn't met, exit 0
            exit 0
        fi
        echo "update-initramfs: failed for ${initramfs} with $mkinitramfs_return." >&2
        exit $mkinitramfs_return
    fi
}
 
# lilo call
run_lilo()
{
    # show lilo errors on failure
    if ! lilo -t  > /dev/null 2>&1 ; then
        echo "ERROR lilo fails for new ${initramfs}:" >&2
        echo
        lilo -t
    fi
    lilo
}
 
# Invoke bootloader
run_bootloader()
{
    # invoke policy conformant bootloader hooks
    if [ -d /etc/initramfs/post-update.d/ ]; then
        run-parts --arg=${version} --arg=${initramfs} \
            /etc/initramfs/post-update.d/
        return 0
    fi
}
 
compare_sha1()
{
    sha1sum "${initramfs}" | diff "${STATEDIR}/${version}" - >/dev/null 2>&1
    return $?
}
 
# Note that this must overwrite so that updates work.
set_sha1()
{
    sha1sum "${initramfs}" > "${STATEDIR}/${version}"
}
 
delete_sha1()
{
    rm -f "${STATEDIR}/${version}"
}
 
# ro /boot is not modified
ro_boot_check()
{
    # check irrelevant inside of a chroot
    if [ ! -r /proc/mounts ] || chrooted; then
        return 0
    fi
 
    boot_opts=$(awk '/boot/{if ((match($4, /^ro/) || match($4, /,ro/)) \
        && $2 == "/boot") print "ro"}' /proc/mounts)
    if [ -n "${boot_opts}" ]; then
        echo "WARNING: /boot is ro mounted."
        echo "update-initramfs: Not updating ${initramfs}"
        exit 0
    fi
}
 
get_sorted_versions()
{
    version_list=""
 
    for gsv_x in "${STATEDIR}"/*; do
        gsv_x="$(basename "${gsv_x}")"
        if [ "${gsv_x}" = '*' ]; then
            return 0
        fi
        worklist=""
        for gsv_i in $version_list; do
            if dpkg --compare-versions "${gsv_x}" '>' "${gsv_i}"; then
                worklist="${worklist} ${gsv_x} ${gsv_i}"
                gsv_x=""
            else
                worklist="${worklist} ${gsv_i}"
            fi
        done
        if [ "${gsv_x}" != "" ]; then
            worklist="${worklist} ${gsv_x}"
        fi
        version_list="${worklist}"
    done
 
    verbose "Available versions: ${version_list}"
}
 
set_current_version()
{
    if [ -f /boot/initrd.img-`uname -r` ]; then
        version=`uname -r`
    fi
}
 
set_linked_version()
{
    linktarget=
    if [ -e /initrd.img ] && [ -L /initrd.img ]; then
        linktarget="$(basename "$(readlink /initrd.img)")"
    fi
 
    if [ -e /boot/initrd.img ] && [ -L /boot/initrd.img ]; then
        linktarget="$(basename "$(readlink /boot/initrd.img)")"
    fi
 
    if [ -z "${linktarget}" ]; then
        return
    fi
 
    version="${linktarget##initrd.img-}"
}
 
set_highest_version()
{
    get_sorted_versions
    if [ -z "${version_list}" ]; then
        version=
        return
    fi
    set -- ${version_list}
    version=${1}
}
 
create()
{
    if [ -z "${version}" ]; then
        usage "Create mode requires a version argument"
    fi
 
    set_initramfs
 
    if [ "${takeover}" = 0 ]; then
        if version_exists "${version}"; then
            panic "Cannot create version ${version}: already exists"
        fi
 
        if [ -e "${initramfs}" ]; then
            panic "${initramfs} already exists, cannot create."
        fi
    fi
 
    generate_initramfs
}
 
update()
{
    #update_initramfs定义在/etc/initramfs-tools/update_initramfs.conf文件中
    #在本文件开始处被包含进来，值为update_initramfs=yes
    if [ "${update_initramfs}" = "no" ]; then
        echo "update-initramfs: Not updating initramfs."
        exit 0
    fi
 
    if [ -z "${version}" ]; then
        set_highest_version
    fi
 
    if [ -z "${version}" ]; then
        set_linked_version
    fi
 
    if [ -z "${version}" ]; then
        #等效version=`uname -r`
        set_current_version
    fi
 
    if [ -z "${version}" ]; then
        verbose "Nothing to do, exiting."
        exit 0
    fi
    #initramfs="/boot/initrd.img-`uname -r`"
    set_initramfs
 
    ro_boot_check
 
    altered_check
 
    backup_initramfs
    #准备调用mkinitramfs,进入函数generate_initramfs
    generate_initramfs
    #如果系统中存在/etc/initramfs/post-update.d/，就调用函数run_bootloader,ubuntu12.04并不存在这个目录
    run_bootloader
 
    backup_booted_initramfs
}
 
delete()
{
    if [ -z "${version}" ]; then
        usage "Delete mode requires a version argument"
    fi
 
    set_initramfs
 
    if [ "${takeover}" = 0 ]; then
        if [ ! -e "${initramfs}" ]; then
            panic "Cannot delete ${initramfs}, doesn't exist."
        fi
 
        if ! version_exists "${version}"; then
            panic "Cannot delete version ${version}: Not created by this utility."
        fi
    fi
 
    altered_check
 
    echo "update-initramfs: Deleting ${initramfs}"
 
    delete_sha1
 
    rm -f "${initramfs}" "${initramfs}.bak"
}
 
# Check for update mode on existing and modified initramfs
altered_check()
{
    # No check on takeover
    [ "${takeover}" = 1 ] && return 0
    if [ ! -e "${initramfs}" ]; then
        mild_panic "${initramfs} does not exist. Cannot update."
    fi
    if ! compare_sha1; then
        echo "update-initramfs: ${initramfs} has been altered." >&2
        mild_panic "update-initramfs: Cannot update. Override with -t option."
    fi
}
 
# Defaults
verbose=0
yes=0
# We default to takeover=1 in Ubuntu, but not Debian
takeover=1
 
##
#可选参数-k和-b后面带其他参数
#参数存放到flag中，供case判断
while getopts "k:cudyvtb:h?" flag; do
    case "${flag}" in
    k)
        #-k 后面有值，则保存在OPTARG(-k kernel version)
        version="${OPTARG}"
        ;;
    c)
        mode="c"
        ;;
    d)
        mode="d"
        ;;
    u)
        mode="u"
        ;;
    v)
        verbose="1"
        ;;
    y)
        yes="1"
        ;;
    t)
        takeover="1"
        ;;
    b)
        BOOTDIR="${OPTARG}"
        if [ ! -d "${BOOTDIR}" ]; then
            echo "Error: ${BOOTDIR} is not a directory." >&2
            exit 1
        fi
        ;;
    h|?)
        usage
        ;;
    esac
done
#常见的获取参数的最后一项的方法
shift $((${OPTIND} - 1))
 
if [ $# -ne 0 ]; then
    echo "Invalid argument for option -k." >&2
    usage
fi
 
# Validate arguments
#${mode}为空
if [ -z "${mode}" ]; then
    usage "You must specify at least one of -c, -u, or -d."
fi
 
#如果输入-k all 或者/etc/initramfs-tools/update-initramfs中的update_initramfs的值为all
if [ "${version}" = "all" ] \
    || ( [ "${update_initramfs}" = "all" ] && [ -z "${version}" ] ); then
    : FIXME check for --yes, and if not ask are you sure
    get_sorted_versions
    if [ -z "${version_list}" ]; then
        verbose "Nothing to do, exiting."
        exit 0
    fi
 
    OPTS="-b ${BOOTDIR}"
    if [ "${verbose}" = "1" ]; then
        OPTS="${OPTS} -v"
    fi
    if [ "${takeover}" = "1" ]; then
        OPTS="${OPTS} -t"
    fi
    if [ "${yes}" = "1" ]; then
        OPTS="${OPTS} -y"
    fi
    for u_version in ${version_list}; do
        verbose "Execute: ${0} -${mode} -k \"${u_version}\" ${OPTS}"
        "${0}" -${mode} -k "${u_version}" ${OPTS}
    done
    exit 0
fi
 
#只讨论update-initramfs -u的情况
case "${mode}" in
    c)
        create
        ;;
    d)
        delete
        ;;
    u)
        #-u 则调用update函数
        update
        ;;
esac

 

如果你耐心够好，看到这，差不多也该跟着执行流进入到mkinitramfs脚本。update函数的结尾依次执行generate_initramfs函数和mkinitramfs命令。就此进入mkinitramfs脚本。mkinitramfs脚本开始处也是定义一些变量，然后include两个重要的辅助脚本/usr/share/initramfs-tools/scripts/functions和/usr/share/initramfs-tools/hook-functions。一些重要的函数定义在这两个脚本中。mkinitramfs在这两个脚本的辅助下完成了前述临时initrd目录的制作

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#!/bin/sh
 
umask 0022
export PATH='/usr/bin:/sbin:/bin'
 
# Defaults
keep="n"
CONFDIR="/etc/initramfs-tools"
verbose="n"
#如果/bin/busybox文件夹存在 变量BUSYBOXDIR=/bin
test -e /bin/busybox && BUSYBOXDIR=/bin
test -e /usr/lib/initramfs-tools/bin/busybox && BUSYBOXDIR=/usr/lib/initramfs-tools/bin
export BUSYBOXDIR
 
OPTIONS=`getopt -o c:d:ko:r:v -n "$0" -- "$@"`
 
# Check for non-GNU getopt
if [ $? != 0 ] ; then echo "W: non-GNU getopt" >&2 ; exit 1 ; fi
 
eval set -- "$OPTIONS"
#update-initramfs调用mkinitramfs时命令为
#mkinitramfs -o /boot/initrd.img-`uname -r`.new ${version},因此进入-o分支
while true; do
    case "$1" in
    -c)
        compress="$2"
        shift 2
        ;;
    -d)
        CONFDIR="$2"
        shift 2
        if [ ! -d "${CONFDIR}" ]; then
            echo "${0}: ${CONFDIR}: Not a directory" >&2
            exit 1
        fi
        ;;
    -o)
        #outfile=/boot/initrd.img-`uname -r`.new
        outfile="$2"
        shift 2
        ;;
    -k)
        keep="y"
        shift
        ;;
    -r)
        ROOT="$2"
        shift 2
        ;;
    -v)
        verbose="y"
        shift
        ;;
    --)
        shift
        break
        ;;
    *)
        echo "Internal error!" >&2
        exit 1
        ;;
    esac
done
 
# For dependency ordered mkinitramfs hook scripts.
#引用这两处的文件 这是一些帮助函数
. /usr/share/initramfs-tools/scripts/functions
. /usr/share/initramfs-tools/hook-functions
 
#引用/etc/initramfs-tools/initramfs.conf 这个文件有关于本地启动或者nfs启动的信息
. "${CONFDIR}/initramfs.conf"
EXTRA_CONF=''
#/usr/share/initramfs-tools/conf.d/目录下为空
#/etc/initramfs-tools/initramfs.conf/conf.d/ 目录下只有resume文件
for i in /usr/share/initramfs-tools/conf.d/* ${CONFDIR}/conf.d/*; do
    [ -e $i ] && EXTRA_CONF="${EXTRA_CONF} $(basename $i \
        | grep '^[[:alnum:]][[:alnum:]\._-]*$' | grep -v '\.dpkg-.*$')";
done
# FIXME: deprecated those settings on mkinitramfs run
#    these conf dirs are for boot scripts and land on initramfs
for i in ${EXTRA_CONF}; do
    if [ -e  ${CONFDIR}/conf.d/${i} ]; then
        . ${CONFDIR}/conf.d/${i}
    elif [ -e  /usr/share/initramfs-tools/conf.d/${i} ]; then
        . /usr/share/initramfs-tools/conf.d/${i}
    fi
done
 
# source package confs
for i in /usr/share/initramfs-tools/conf-hooks.d/*; do
    if [ -e "${i}" ]; then
        . "${i}"
    fi
done
#UMASK 非空 不过没找到何处设置了这个变量
if [ -n "${UMASK:-}" ]; then
    umask "${UMASK}"
fi
#outfile为空 也不成立
if [ -z "${outfile}" ]; then
    usage
fi
 
#生成新的空的initrd.img-`uname -r`文件
touch "$outfile"
outfile="$(readlink -f "$outfile")"
 
# And by "version" we really mean path to kernel modules
# This is braindead, and exists to preserve the interface with mkinitrd
if [ ${#} -ne 1 ]; then
    version="$(uname -r)"
else
    version="${1}"
fi
 
# Check that we're using a new enough kernel version, first for ourselves,
# then for each of the hooks, which can have a MINKVER variable defined
check_minkver ${version}
check_minkver ${version} /usr/share/initramfs-tools/hooks
check_minkver ${version} ${CONFDIR}/hooks
 
case "${version}" in
#/lib/modules/*/目录下除了/以外的文件，这是指除了该目录下除了子目录以外的所有文件?
/lib/modules/*/[!/]*)
    ;;
/lib/modules/[!/]*)
    version="${version#/lib/modules/}"
    version="${version%%/*}"
    ;;
esac
 
case "${version}" in
*/*)
    echo "$PROG: ${version} is not a valid kernel version" >&2
    exit 1
    ;;
esac
 
# Check userspace and kernel support for compressed initramfs images
if [ -z "${compress:-}" ]; then
    #COMPRESS=gzip gzip压缩
    compress=${COMPRESS}
else
    COMPRESS=${compress}
fi
 
if ! command -v "${compress}" >/dev/null 2>&1; then
    compress=gzip
    [ "${verbose}" = y ] && \
        echo "No ${COMPRESS} in ${PATH}, using gzip"
    COMPRESS=gzip
fi
 
#/boot/config-${version}匹配以config_rd_${COMPRESS%p}开头
if ! `grep -q -i ^config_rd_${COMPRESS%p} /boot/config-${version}` ; then
    compress=gzip
    [ "${verbose}" = y ] && \
        echo "linux-2.6 misses ${COMPRESS} support, using gzip"
fi
 
[ "${compress}" = lzop ] && compress="lzop -9"
[ "${compress}" = xz ] && compress="xz -8 --check=crc32"
 
if [ -d "${outfile}" ]; then
    echo "${outfile} is a directory" >&2
    exit 1
fi
#要编译内核的版本
MODULESDIR="/lib/modules/${version}"
 
if [ ! -e "${MODULESDIR}" ]; then
    echo "WARNING: missing ${MODULESDIR}"
    echo "Device driver support needs thus be built-in linux image!"
fi
#检测模块依赖性 不存在模块依赖文件 怎生成
if [ ! -e "${MODULESDIR}/modules.dep" ]; then
    depmod ${version}
fi
#在/tmp下生成名为mkinitramfs_fb9BN这样的文件
DESTDIR="$(mktemp -d ${TMPDIR:-/tmp}/mkinitramfs_XXXXXX)" || exit 1
chmod 755 "${DESTDIR}"
 
# do not execute cache_run_scripts() if mounted with noexec
NOEXEC=""
#找到临时文件的挂载点 fs=/
fs=$(df -P $DESTDIR | tail -1 | awk '{print $6}')
if [ -n "$fs" ] && mount | grep -q "on $fs .*noexec" ; then
    NOEXEC=1
fi
 
__TMPCPIOGZ="$(mktemp ${TMPDIR:-/tmp}/mkinitramfs-OL_XXXXXX)" || exit 1
 
DPKG_ARCH=`dpkg --print-architecture`
 
# Export environment for hook scripts.
#
export MODULESDIR
export version
export CONFDIR
export DESTDIR
export DPKG_ARCH
export verbose
export MODULES
export BUSYBOX
export COMPCACHE_SIZE
 
# Private, used by 'catenate_cpiogz'.
export __TMPCPIOGZ
 
#在/tmp/mkinitramfs_fb9BNB文件夹下生成bin conf/conf.d etc lib/modules run sbin scripts /lib/modules/${version}这些文件夹
#这是在制作根文件系统
for d in bin conf/conf.d etc lib/modules run sbin scripts ${MODULESDIR}; do
    mkdir -p "${DESTDIR}/${d}"
done
 
# Copy the modules.order file in
if [ -f "${MODULESDIR}/modules.order" ]; then
    cp -p "${MODULESDIR}/modules.order" \
        "${DESTDIR}${MODULESDIR}/modules.order"
fi
 
# MODULES=list case.  Always honour.
for x in "${CONFDIR}/modules" /usr/share/initramfs-tools/modules.d/*; do
    if [ -f "${x}" ]; then
        #add_modules_from_file定义在/usr/share/initramfs-tools/hook-functions中
        #这里就是add_modules_from_file /etc/initramfs-tools/modules
        #/etc/initramfs-tools/modules中含有要添加到initrd镜像中的modules
        add_modules_from_file "${x}"
    fi
done
 
# 没有找到MODULES定义的文件 按注释MODULES=most
# MODULES=most is default
case "${MODULES}" in
dep)
    dep_add_modules
    ;;
most)
    #auto_add_modules仍然定义在/usr/share/initramfs-tools/hook-functions中
    auto_add_modules
    ;;
netboot)
    auto_add_modules base
    auto_add_modules net
    ;;
list)
    # nothing to add
    ;;
*)
    echo "W: mkinitramfs: unsupported MODULES setting: ${MODULES}."
    echo "W: mkinitramfs: Falling back to MODULES=most."
    auto_add_modules
    ;;
esac
 
# Resolve hidden dependencies
hidden_dep_add_modules
 
# First file executed by linux-2.6
#拷贝init文件，init是系统启动后进入根文件系统之后启动的第一个进程
cp -p /usr/share/initramfs-tools/init ${DESTDIR}/init
 
# add existant boot scripts
#递归搜索/usr/share/initramfs-tools/scripts/目录下所有配置文件(init-top/all_generic_ide udev...)，如果文件中不含有"OPTION="字段，
#则在${DESTDIR}/scripts/目录中创建对应目录，并把文件拷贝到该目录中
for b in $(cd /usr/share/initramfs-tools/scripts/ && find . \
    -regextype posix-extended -regex '.*/[[:alnum:]\._-]+$' -type f); do
    option=$(sed '/^OPTION=/!d;$d;s/^OPTION=//;s/[[:space:]]*$//' "/usr/share/initramfs-tools/scripts/${b}")
    [ -z "${option}" ] || eval test -n \"\${$option}\" -a \"\${$option}\" != \"n\" || continue
 
    [ -d "${DESTDIR}/scripts/$(dirname "${b}")" ] \
        || mkdir -p "${DESTDIR}/scripts/$(dirname "${b}")"
    cp -p "/usr/share/initramfs-tools/scripts/${b}" \
        "${DESTDIR}/scripts/$(dirname "${b}")/"
done
#对于/etc/initramfs-tools/scripts下的文件使用同样的操作
for b in $(cd "${CONFDIR}/scripts" && find . \
    -regextype posix-extended -regex '.*/[[:alnum:]\._-]+$' -type f); do
    option=$(sed '/^OPTION=/!d;$d;s/^OPTION=//;s/[[:space:]]*$//' "${CONFDIR}/scripts/${b}")
    [ -z "${option}" ] || eval test -n \"\${$option}\" -a \"\${$option}\" != \"n\" || continue
 
    [ -d "${DESTDIR}/scripts/$(dirname "${b}")" ] \
        || mkdir -p "${DESTDIR}/scripts/$(dirname "${b}")"
    cp -p "${CONFDIR}/scripts/${b}" "${DESTDIR}/scripts/$(dirname "${b}")/"
done
 
echo "DPKG_ARCH=${DPKG_ARCH}" > ${DESTDIR}/conf/arch.conf
#把/etc/initramfs-tools/initramfs.conf拷贝到${DESTDIR}/conf目录下，
#这个文件涉及本地启动和nfs启动,以及加载的驱动MODULES=most
cp -p "${CONFDIR}/initramfs.conf" ${DESTDIR}/conf
for i in ${EXTRA_CONF}; do
    if [ -e "${CONFDIR}/conf.d/${i}" ]; then
        copy_exec "${CONFDIR}/conf.d/${i}" /conf/conf.d
    elif [ -e "/usr/share/initramfs-tools/conf.d/${i}" ]; then
        copy_exec "/usr/share/initramfs-tools/conf.d/${i}" /conf/conf.d
    fi
done
 
# ROOT hardcoding
if [ -n "${ROOT:-}" ]; then
    echo "ROOT=${ROOT}" > ${DESTDIR}/conf/conf.d/root
fi
 
if ! command -v ldd >/dev/null 2>&1 ; then
    echo "WARNING: no ldd around - install libc-bin" >&2
    exit 1
fi
#copy_exec定义在hook-functions中
copy_exec /usr/lib/initramfs-tools/bin/wait-for-root /sbin
 
# module-init-tools
copy_exec /sbin/modprobe /sbin
copy_exec /sbin/rmmod /sbin
mkdir -p "${DESTDIR}/etc/modprobe.d"
#拷贝/etc/modprobe.d/下文件到${DESTDIR}/etc/modprobe.d/下
#这些文件关系到modprobe mod时的行为
cp -a /etc/modprobe.d/* "${DESTDIR}/etc/modprobe.d/"
 
# util-linux
copy_exec /sbin/blkid /sbin
 
# workaround: libgcc always needed on old-abi arm
if [ "$DPKG_ARCH" = arm ] || [ "$DPKG_ARCH" = armeb ]; then
    cp -a /lib/libgcc_s.so.1 "${DESTDIR}/lib/"
fi
 
run_scripts /usr/share/initramfs-tools/hooks optional
run_scripts "${CONFDIR}"/hooks optional
 
# cache boot run order
if [ -n "$NOEXEC" ]; then
    echo "W: TMPDIR is mounted noexec, will not cache run scripts."
else
    for b in $(cd "${DESTDIR}/scripts" && find . -mindepth 1 -type d); do
        cache_run_scripts "${DESTDIR}" "/scripts/${b#./}"
    done
fi
 
# generate module deps
#生成模块依赖文件
depmod -a -b "${DESTDIR}" ${version}
rm -f "${DESTDIR}/lib/modules/${version}"/modules.*map
 
# make sure that library search path is up to date
#拷贝/etc/ld.so.conf*到initrd目录结构中对应位置，可执行程序可能依赖非标准路径下的so文件，
#因此在此调用ldconfig -r分析/${DESTDIR}/etc/ld.so.conf*中列出的非标准搜索路径，并生成
#缓存文件加速链接速度
#ldconfig -r ROOT : 此选项改变应用程序的根目录为ROOT(是调用chroot函数实现的).选择此项时,系统默认的配置文件
#/etc/ld.so.conf,实际对应的为 ROOT/etc/ld.so.conf.如用-r /usr/zzz时,打开配置文件 /etc/ld.so.conf时,实际打开的
#是/usr/zzz/etc/ld.so.conf文件.用此选项,可以大大增加动态链接库管理的灵活性
cp -ar /etc/ld.so.conf* "$DESTDIR"/etc/
if ! ldconfig -r "$DESTDIR" ; then
    [ $(id -u) != "0" ] \
    && echo "ldconfig might need uid=0 (root) for chroot()" >&2
fi
 
# Apply DSDT to initramfs
if [ -e "${CONFDIR}/DSDT.aml" ]; then
    copy_exec "${CONFDIR}/DSDT.aml" /
fi
 
# Remove any looping or broken symbolic links, since they break cpio.
[ "${verbose}" = y ] && xargs_verbose="-t"
(cd "${DESTDIR}" && find . -type l -printf '%p %Y\n' | sed -n 's/ [LN]$//p' \
    | xargs ${xargs_verbose:-} -rL1 rm -f)
 
# dirty hack for armhf's double-linker situation; if we have one of
# the two known eglibc linkers, nuke both and re-create sanity
if [ "$DPKG_ARCH" = armhf ]; then
    if [ -e "${DESTDIR}/lib/arm-linux-gnueabihf/ld-linux.so.3" ] || \
       [ -e "${DESTDIR}/lib/ld-linux-armhf.so.3" ]; then
        rm -f "${DESTDIR}/lib/arm-linux-gnueabihf/ld-linux.so.3"
        rm -f "${DESTDIR}/lib/ld-linux-armhf.so.3"
        cp -aL /lib/ld-linux-armhf.so.3 "${DESTDIR}/lib/"
        ln -sf /lib/ld-linux-armhf.so.3 "${DESTDIR}/lib/arm-linux-gnueabihf/ld-linux.so.3"
    fi
fi
 
[ "${verbose}" = y ] && echo "Building cpio ${outfile} initramfs"
(
# work around lack of "set -o pipefail" for the following pipe:
# cd "${DESTDIR}" && find . | cpio --quiet -R 0:0 -o -H newc | gzip >"${outfile}" || exit 1
#这是创建initramfs的最后一步了 调用cpio和gzip 打包并压缩initramfs目录
exec 3>&1
eval `
    # http://cfaj.freeshell.org/shell/cus-faq-2.html
    exec 4>&1 >&3 3>&-
    cd  "${DESTDIR}"
    {
        find . 4>&-; echo "ec1=$?;" >&4
    } | {
        cpio --quiet -R 0:0 -o -H newc 4>&-; echo "ec2=$?;" >&4
    } | ${compress} >"${outfile}"
    echo "ec3=$?;" >&4
`
if [ "$ec1" -ne 0 ]; then
    echo "E: mkinitramfs failure find $ec1 cpio $ec2 $compress $ec3"
    exit "$ec1"
fi
if [ "$ec2" -ne 0 ]; then
    echo "E: mkinitramfs failure cpio $ec2 $compress $ec3"
    exit "$ec2"
fi
if [ "$ec3" -ne 0 ]; then
    echo "E: mkinitramfs failure $compress $ec3"
    exit "$ec3"
fi
) || exit 1
 
if [ -s "${__TMPCPIOGZ}" ]; then
    cat "${__TMPCPIOGZ}" >>"${outfile}" || exit 1
fi
 
if [ "${keep}" = "y" ]; then
    echo "Working files in ${DESTDIR} and overlay in ${__TMPCPIOGZ}"
else
    rm -rf "${DESTDIR}"
    rm -rf "${__TMPCPIOGZ}"
fi
 
exit 0

 

最后贴出hook-functions中用到的几个函数的注释

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force_load() 
{ 
        manual_add_modules ${@} 
        #调用mkinitramfs时设置DESTDIR=/tmp/mkinitramfs_fb9BNB---一个临时根文件系统结构， 
        #把/etc/initramfs-tools/modules中读到的modules加入到/tmp/mkinitramfs_fb9BNB/conf/modules中 
        #前面已经说过update-initramfs -u时会将/etc/initramfs-tools/modules文件中的模块加入到initrd 
        #文件,作为引导加载modules，看来就是在这实现的 
        echo "${@}" >>"${DESTDIR}/conf/modules" 
} 

 

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add_modules_from_file() 
{ 
# Sanity check 
if [ ! -e "${1}" ]; then 
echo "W: add_modules_from_file: arg1='${1}' does not exist." >&2 
return 
fi 
#从/etc/initramfs-tools/modules中读取非注释的行，模块名和参数分别读入module和args 
#并调用force_load函数 
grep '^[^#]' ${1} | while read module args; do 
[ -n "$module" ] || continue 
force_load "${module}" "${args}" 
done 
} 

 

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# $1 = file to copy to ramdisk 
# $2 (optional) Name for the file on the ramdisk 
# Location of the image dir is assumed to be $DESTDIR 
# We never overwrite the target if it exists. 
#拷贝可执行程序到$DESTDIR对应目录下，同时解决可执行程序的依赖库(ldd) 
copy_exec() { 
local src target x nonoptlib 
local libname dirname 
   
   
src="${1}" 
#如果$2(可执行程序所在的目录)为空 则返回$1的值  
target="${2:-$1}" 
#可执行程序不存在就return，否则往下执行 
[ -f "${src}" ] || return 1 
if [ -d "${DESTDIR}/${target}" ]; then 
# check if already copied 
#目录存在并且exe存在则返回 
[ -e "${DESTDIR}/$target/${src##*/}" ] && return 0 
else 
#目录不存在 则创建目录 
[ -e "${DESTDIR}/$target" ] && return 0 
#FIXME: inst_dir 
mkdir -p "${DESTDIR}/${target%/*}" 
fi 
#拷贝host系统的exe文件到initrd目录结构中 
[ "${verbose}" = "y" ] && echo "Adding binary ${src}" 
cp -pL "${src}" "${DESTDIR}/${target}" 
# Copy the dependant libraries 
#ldd的输出形式为 xxx ==> yyy 
#for循环中的第一个sed是提取第3列中的yyy 
for x in $(ldd ${src} 2>/dev/null | sed -e ' 
/\//!d;/linux-gate/d;/ {s/.*=>[[:blank:]]*[[:blank:]]∗.*/\1/};s/[[:blank:]]*[[:blank:]]∗ (.*)/\1/' 2>/dev/null); do 
   
   
# Try to use non-optimised libraries where possible. 
# We assume that all HWCAP libraries will be in tls, 
# sse2, vfp or neon. 
nonoptlib=$(echo "${x}" | sed -e 's#/lib/tls∥i686∥sse2∥neon∥vfp.*/lib.∗#/lib/\2#') 
   
if [ -e "${nonoptlib}" ]; then 
x="${nonoptlib}" 
fi 
   
   
libname=$(basename "${x}") 
dirname=$(dirname "${x}") 
# FIXME inst_lib 
#从host机上拷贝依赖库到initrd目录结构中 
mkdir -p "${DESTDIR}/${dirname}" 
if [ ! -e "${DESTDIR}/${dirname}/${libname}" ]; then 
cp -pL "${x}" "${DESTDIR}/${dirname}" 
[ "${verbose}" = "y" ] && echo "Adding library ${x}" || true 
fi 
done 
} 

 

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