openWRT自学---对官方的开发指导文档的解读和理解 记录1：编译一个package

针对的是：http://kamikaze.openwrt.org/docs/openwrt.html#x1-390002

1.If you want, you can also modify the kernel config for the selected target system. simply run "make kernel_menuconfig" and the build system will unpack the kernel sources (if necessary), run menuconfig inside of the kernel tree, and then copy the kernel config to target/linux/<platform>/config so that it is preserved over "make clean" calls.  ---- 如果你愿意，你也可以修改内核配置为选定的目标系统。简单地运行“make kernel_menuconfig”和构建系统将解压缩内核源代码（如果有必要）。此命令会展示针对内核的配置选择界面，然后其结果再复制内核配置到目标/ linux的/<platform>/配置。这样得到的针对内核的.config文件，在"make clean"后依然是保留的。

2.During the build process, buildroot will download all sources to the "dl" directory and will start patching and compiling them in the "build_dir/<arch> " directory. When finished, the resulting firmware will be in the "bin" directory and packages will be in the "bin/packages" directory -- 在编译过程中，buildroot会将所有的源下载到“dl”目录下，并在“build_dir/<arch>”目录中对它们进行patch和编译。完成后，所产生的固件将在“bin”目录，而各个package将在“bin/packages"目录中

3.openwrt中的一个典型的package目录结构：

• package/<name>/Makefile  --- 必须存在；其作用是定义下载包和编译包的步骤
• package/<name>/patches   --- 可有可无；是对所下载包的修复和优化，即补丁
• package/<name>/files        --- 可有可无；是此包特有的启动脚本和配置文件

4.openwrt中的一个典型的package目录结构（以backfire的package/bridge-utils为例）。其makefile的内容如下：

#
# Copyright (C) 2006-2008 OpenWrt.org
#
# This is free software, licensed under the GNU General Public License v2.
# See /LICENSE for more information.
#

include $(TOPDIR)/rules.mk
include $(INCLUDE_DIR)/kernel.mk

PKG_NAME:=bridge-utils    //The name of the package, as seen via menuconfig and ipkg。不过我在CPE上使用opkg list命令，看到的是bridge - 1.4-1；而通过make menuconfig看到的是 bridge（在Base System里面）。 此外，在package中有一个bridge-utils；在feeds/package中也有一个。到底这些如何对应呢？
PKG_RELEASE:=1  //The version of this package Makefile
PKG_SOURCE_URL:=@SF/bridge  //Where to download the sources from (no trailing slash), you can add multiple download sources by separating them with a and a carriage return. @SF表示从SourceForge下载

ifeq ($(CONFIG_LINUX_2_4),y)
  PKG_VERSION:=1.0.6
  PKG_MD5SUM:=9b7dc52656f5cbec846a7ba3299f73bd
endif

ifeq ($(CONFIG_LINUX_2_6),y)
  PKG_VERSION:=1.4  //The upstream version number that we are downloading
  PKG_MD5SUM:=0182fcac3a2b307113bbec34e5f1c673  //A checksum to validate the download
endif

PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz   //The filename of the original sources，这里就是 bridge-utils-1.4.tar.gz

include $(INCLUDE_DIR)/package.mk  //位于 backfire_10.03/include/package.mk，用于定义任何一个package下载的统一的方式脚本

define Package/bridge
  SECTION:=net   //The type of package (currently unused)
  CATEGORY:=Base system   //Which menu it appears in menuconfig: Network, Sound, Utilities, Multimedia ...
  TITLE:=Ethernet bridging configuration utility  //A short description of the package
  URL:=http://bridge.sourceforge.net/   //Where to find the original software
endef

define Package/bridge/description
 Manage ethernet bridging: a way to connect networks together to
 form a larger network.
endef

CONFIGURE_ARGS += \
    --with-linux-headers="$(LINUX_DIR)" \

define Build/Prepare   //这是可选项。A set of commands to unpack and patch the sources. You may safely leave this undefined.
$(call Build/Prepare/Default)
    ( cd $(PKG_BUILD_DIR) ; \   //PKG_BUILD_DIR定义在下载包后将此包解压缩到$(BUILD_DIR)的具体位置。对于此bridge-util包，其位置在backfire_10.03/build_dir/linux-brcm47xx/bridge-utils-1.4 中；同时这就说明用的是package中的，而不是feeds/package中的
        [ -f ./configure ] || { \
            ln -sf configure.in configure.ac ; \
            autoconf ; \
        } \
    )
endef

define Package/bridge/install
    $(INSTALL_DIR) $(1)/usr/sbin   //$(INSTALL_DIR)即为：install -d -m0755  
    $(INSTALL_BIN) $(PKG_BUILD_DIR)/brctl/brctl $(1)/usr/sbin/   //$(INSTALL_BIN)即为: install -m0755
endef

$(eval $(call BuildPackage,bridge))   //这是真正开始执行的位置。BuildPackage定义在package.mk中，其调用的参数是bridge。这样就会走到package.mk中的：define BuildPackage
  $(Build/IncludeOverlay)
  $(eval $(Package/Default))
  $(eval $(Package/$(1)))   //对应就是$(Package/bridge)，从而又找到package/bridge-utils/Makefile中的 define Package/bridge 位置。

再举一个稍微复杂的例子，package/dropbear（一个轻量级的ssh客户端与服务端开源），其目录中包含了：files（内含配置文件和启动脚本），patches（内含补丁）和Makefile；如下是Makefile：

#
# Copyright (C) 2006-2009 OpenWrt.org
#
# This is free software, licensed under the GNU General Public License v2.
# See /LICENSE for more information.
#

include $(TOPDIR)/rules.mk

PKG_NAME:=dropbear  //The name of the package, as seen via menuconfig and ipkg
PKG_VERSION:=0.52  //The upstream version number that we are downloading
PKG_RELEASE:=4  //The version of this package Makefile

PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz   //The filename of the original sources，这里就是 dropbear-0.52.tar.gz
PKG_SOURCE_URL:= \     //下载源码包的url地址，这里就写了多个地址，用回车换行+一个斜杠来排列表示
    http://matt.ucc.asn.au/dropbear/releases/ \
    http://www.mirrors.wiretapped.net/security/cryptography/apps/ssh/dropbear/
PKG_MD5SUM:=1c69ec674481d7745452f68f2ea5597e  //MD5校验和

include $(INCLUDE_DIR)/package.mk  //实际是include了 backfire_10.03/include/package.mk

define Package/dropbear/Default
  URL:=http://matt.ucc.asn.au/dropbear/  //Where to find the original software
endef

define Package/dropbear   //由 BuildPackage 命令调用
  $(call Package/dropbear/Default)
  SECTION:=net  //The type of package (currently unused)
  CATEGORY:=Base system  //Which menu it appears in menuconfig: Network, Sound, Utilities, Multimedia ...
  TITLE:=Small SSH2 client/server  //A short description of the package
endef

define Package/dropbear/description
 A small SSH2 server/client designed for small memory environments.
endef

define Package/dropbear/conffiles  //此项可选，A list of config files installed by this package, one file per line.表示此package会安装的一些配置文件
/etc/dropbear/dropbear_rsa_host_key
/etc/dropbear/dropbear_dss_host_key
/etc/config/dropbear
endef

define Package/dropbearconvert   //这是另一个package，也是从dropbear的源码包里面会得到的。
  $(call Package/dropbear/Default)
  SECTION:=utils
  CATEGORY:=Utilities
  TITLE:=Utility for converting SSH keys
endef

CONFIGURE_ARGS += \
    --with-shared \
    --disable-pam \
    --enable-openpty \
    --enable-syslog \
    $(if $(CONFIG_SHADOW_PASSWORDS),,--disable-shadow) \
    --disable-lastlog \
    --disable-utmp \
    --disable-utmpx \
    --disable-wtmp \
    --disable-wtmpx \
    --disable-loginfunc \
    --disable-pututline \
    --disable-pututxline \
    --disable-zlib

define Build/Configure  //此项可选。用于编译时传递一些自定义参数
    $(SED) 's,^/\* #define PKG_MULTI.*,#define PKG_MULTI,g' $(PKG_BUILD_DIR)/options.h
    $(SED) 's,^#define DO_HOST_LOOKUP,/* & */,g' $(PKG_BUILD_DIR)/options.h
    $(call Build/Configure/Default)
endef

define Build/Compile  //此项可选。表示如何编译源码包
    $(MAKE) -C $(PKG_BUILD_DIR) \
        $(TARGET_CONFIGURE_OPTS) \
        LD="$(TARGET_CC)" \
        PROGRAMS="dropbear dbclient dropbearkey scp" \
        MULTI=1 SCPPROGRESS=1
    $(MAKE) -C $(PKG_BUILD_DIR) \
        $(TARGET_CONFIGURE_OPTS) \
        LD="$(TARGET_CC)" \
        PROGRAMS="dropbearconvert"
endef

define Package/dropbear/install  //A set of commands to copy files out of the compiled source and into the ipkg which is represented by the $(1) directory
    $(INSTALL_DIR) $(1)/usr/sbin
    $(INSTALL_BIN) $(PKG_BUILD_DIR)/dropbearmulti $(1)/usr/sbin/dropbear
    $(INSTALL_DIR) $(1)/usr/bin
    ln -sf ../sbin/dropbear $(1)/usr/bin/scp
    ln -sf ../sbin/dropbear $(1)/usr/bin/ssh
    ln -sf ../sbin/dropbear $(1)/usr/bin/dbclient
    ln -sf ../sbin/dropbear $(1)/usr/bin/dropbearkey
    $(INSTALL_DIR) $(1)/etc/config
    $(INSTALL_DATA) ./files/dropbear.config $(1)/etc/config/dropbear
    $(INSTALL_DIR) $(1)/etc/init.d
    $(INSTALL_BIN) ./files/dropbear.init $(1)/etc/init.d/dropbear
    $(INSTALL_DIR) $(1)/usr/lib/opkg/info
    $(INSTALL_DIR) $(1)/etc/dropbear
    touch $(1)/etc/dropbear/dropbear_rsa_host_key
    touch $(1)/etc/dropbear/dropbear_dss_host_key
endef

define Package/dropbearconvert/install
    $(INSTALL_DIR) $(1)/usr/bin
    $(INSTALL_BIN) $(PKG_BUILD_DIR)/dropbearconvert $(1)/usr/bin/dropbearconvert
endef

$(eval $(call BuildPackage,dropbear))  //调用package.mk中的BuildPackage，开始编译dropbear
$(eval $(call BuildPackage,dropbearconvert))  //调用package.mk中的BuildPackage，开始编译dropbearconvert

在你创建你的 package/<NAME>/ Makefile文件后，新的软件包会自动在下一次运行“make menuconfig时”，出现在菜单中。如果选中，此该package将在下一次make中被自动编译