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