1、研究背景
我们在开发的过程中可能需要移植OpenWRT上没有的软件包，而这些软件包又比较特殊。例如，像busybox那样自带kconfig配置文件供生成菜单配置界面的软件包。我们可以直接在这个软件包根目录下执行make
menuconfig来配置我们需要的功能，保存配置后在这个软件包的源码根目录下直接执行make命令即可编译该软件包。
但是，想将这样的软件包集成到OpenWRT中，就需要把这些配置项都集成到OpenWRT的配置中。考虑到在OpenWRT中，busybox就是一个很典型的集成案例。所以，我们在集成这样的软件包时就可以参考它的集成方式。
下面，我们就以busybox为例进行说明，源码摘自github，如下：
https://github.com/openwrt/openwrt/tree/master/package/utils/busybox
2、OpenWRT如何集成busybox的配置项
busybox本身也自带了很多配置选项，但实际上我们却可以在OpenWRT总的配置项中对其进行配置，而不需要进入busybox目录单独对其做进行配置。
通过查看busybox包的顶层Makefile，可以发现，OpenWRT是这样集成busybox的配置项的。不改动busybox原来的配置项，而是针对busybox每个配置项都另外生成一个对应的配置项，用于集成到OpenWRT中。
这些配置项被定义在openwrt/package/utils/busybox/config目录中。并通过 openwrt/package/utils/busybox/Config.in文件连接到OpenWRT总的配置项中。
接下来，我们就结合代码(openwrt/package/utils/busybox/Makefile)来分析一下这个OpenWRT集成busybox配置项的过程，代码如下所示：
1 # SPDX-License-Identifier: GPL-2.0-or-later 2 # 3 # Copyright (C) 2006-2021 OpenWrt.org 4 5 include $(TOPDIR)/rules.mk 6 7 PKG_NAME:=busybox 8 PKG_VERSION:=1.33.1 9 PKG_RELEASE:=$(AUTORELEASE) 10 PKG_FLAGS:=essential 11 12 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2 13 PKG_SOURCE_URL:=https://www.busybox.net/downloads \ 14 http://sources.buildroot.net 15 PKG_HASH:=12cec6bd2b16d8a9446dd16130f2b92982f1819f6e1c5f5887b6db03f5660d28 16 17 PKG_BUILD_DEPENDS:=BUSYBOX_CONFIG_PAM:libpam 18 PKG_BUILD_PARALLEL:=1 19 PKG_CHECK_FORMAT_SECURITY:=0 20 21 PKG_LICENSE:=GPL-2.0 22 PKG_LICENSE_FILES:=LICENSE archival/libarchive/bz/LICENSE 23 PKG_CPE_ID:=cpe:/a:busybox:busybox 24 25 BUSYBOX_SYM=$(if $(CONFIG_BUSYBOX_CUSTOM),CONFIG,DEFAULT) 26 BUSYBOX_IF_ENABLED=$(if $(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_$(1)),$(2)) 27 28 ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_FEATURE_SUID),) 29 PKG_FILE_MODES:=/bin/busybox:root:root:4755 30 endif 31 32 include $(INCLUDE_DIR)/package.mk 33 34 ifeq ($(DUMP),) 35 STAMP_CONFIGURED:=$(strip $(STAMP_CONFIGURED))_$(shell grep '^CONFIG_BUSYBOX_' $(TOPDIR)/.config | $(MKHASH) md5) 36 endif 37 38 # All files provided by busybox will serve as fallback alternatives by opkg. 39 # There should be no need to enumerate ALTERNATIVES entries here 40 define Package/busybox/Default 41 SECTION:=base 42 CATEGORY:=Base system 43 MAINTAINER:=Felix Fietkau <nbd@nbd.name> 44 TITLE:=Core utilities for embedded Linux 45 URL:=http://busybox.net/ 46 DEPENDS:=+BUSYBOX_CONFIG_PAM:libpam +BUSYBOX_CONFIG_NTPD:jsonfilter 47 USERID:=ntp=123:ntp=123 48 endef 49 50 define Package/busybox 51 $(call Package/busybox/Default) 52 CONFLICTS:=busybox-selinux 53 VARIANT:=default 54 endef 55 56 define Package/busybox-selinux 57 $(call Package/busybox/Default) 58 TITLE += with SELinux support 59 DEPENDS += +libselinux 60 VARIANT:=selinux 61 PROVIDES:=busybox 62 endef 63 64 define Package/busybox/description 65 The Swiss Army Knife of embedded Linux. 66 It slices, it dices, it makes Julian Fries. 67 endef 68 69 define Package/busybox/config 70 source "$(SOURCE)/Config.in" 71 endef 72 73 ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_FEATURE_SYSLOG)$(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_FEATURE_SYSLOGD_CFG),) 74 define Package/busybox/conffiles/syslog 75 /etc/syslog.conf 76 endef 77 endif 78 79 ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_CROND),) 80 define Package/busybox/conffiles/crond 81 /etc/crontabs/ 82 endef 83 endif 84 85 define Package/busybox/conffiles 86 $(Package/busybox/conffiles/syslog) 87 $(Package/busybox/conffiles/crond) 88 endef 89 90 Package/busybox-selinux/conffiles = $(Package/busybox/conffiles) 91 92 ifndef CONFIG_USE_MUSL 93 LDLIBS:=m crypt 94 endif 95 96 LDLIBS += $(call BUSYBOX_IF_ENABLED,PAM,pam pam_misc pthread) 97 98 ifeq ($(CONFIG_USE_GLIBC),y) 99 LDLIBS += $(call BUSYBOX_IF_ENABLED,NSLOOKUP,resolv) 100 endif 101 102 ifeq ($(BUILD_VARIANT),selinux) 103 LDLIBS += selinux sepol 104 endif 105 106 TARGET_CFLAGS += -flto 107 TARGET_LDFLAGS += -flto=jobserver -fuse-linker-plugin 108 109 MAKE_VARS := 110 MAKE_FLAGS += \ 111 EXTRA_CFLAGS="$(TARGET_CFLAGS) $(TARGET_CPPFLAGS)" \ 112 EXTRA_LDFLAGS="$(TARGET_LDFLAGS)" \ 113 LDLIBS="$(LDLIBS)" \ 114 LD="$(TARGET_CC)" \ 115 SKIP_STRIP=y 116 ifneq ($(findstring c,$(OPENWRT_VERBOSE)),) 117 MAKE_FLAGS += V=1 118 endif 119 120 define Build/Configure 121 rm -f $(PKG_BUILD_DIR)/.config 122 touch $(PKG_BUILD_DIR)/.config 123 ifeq ($(DEVICE_TYPE),nas) 124 echo "CONFIG_HDPARM=y" >> $(PKG_BUILD_DIR)/.config 125 endif 126 ifeq ($(BUILD_VARIANT),selinux) 127 cat $(TOPDIR)/$(SOURCE)/selinux.config >> $(PKG_BUILD_DIR)/.config 128 endif 129 grep 'CONFIG_BUSYBOX_$(BUSYBOX_SYM)' $(TOPDIR)/.config | sed -e "s,\\(# \)\\?CONFIG_BUSYBOX_$(BUSYBOX_SYM)_\\(.*\\),\\1CONFIG_\\2,g" >> $(PKG_BUILD_DIR)/.config 130 yes 'n' | $(MAKE) -C $(PKG_BUILD_DIR) $(MAKE_FLAGS) oldconfig 131 endef 132 133 define Build/Compile 134 $(call Build/Compile/Default, \ 135 CONFIG_PREFIX="$(PKG_INSTALL_DIR)" \ 136 all install \ 137 ) 138 endef 139 140 define Package/busybox/install 141 $(INSTALL_DIR) $(1)/etc/init.d 142 $(INSTALL_DIR) $(1)/usr/sbin 143 $(CP) $(PKG_INSTALL_DIR)/* $(1)/ 144 ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_FEATURE_SYSLOG)$(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_FEATURE_SYSLOGD_CFG),) 145 touch $(1)/etc/syslog.conf 146 endif 147 ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_CROND),) 148 $(INSTALL_BIN) ./files/cron $(1)/etc/init.d/cron 149 $(INSTALL_DIR) $(1)/etc/crontabs 150 endif 151 ifneq ($(CONFIG_BUSYBOX_$(BUSYBOX_SYM)_NTPD),) 152 $(INSTALL_BIN) ./files/sysntpd $(1)/etc/init.d/sysntpd 153 $(INSTALL_BIN) ./files/ntpd-hotplug $(1)/usr/sbin/ntpd-hotplug 154 $(INSTALL_DIR) $(1)/etc/capabilities $(1)/usr/share/acl.d 155 $(INSTALL_DATA) ./files/ntpd.capabilities $(1)/etc/capabilities/ntpd.json 156 $(INSTALL_DATA) ./files/ntpd_acl.json $(1)/usr/share/acl.d/ntpd.json 157 endif 158 -rm -rf $(1)/lib64 159 endef 160 161 Package/busybox-selinux/install = $(Package/busybox/install) 162 163 $(eval $(call BuildPackage,busybox)) 164 $(eval $(call BuildPackage,busybox-selinux))
从该Makefile的第69~71行可以看出，对于OpenWRT而言，busybox的配置项就来源于$(SOURCE)/Config.in文件。
接下来，我们看下openwrt/package/utils/busybox/Config.in这个busybox总的配置文件。代码如下所示：
1 if PACKAGE_busybox || PACKAGE_busybox-selinux 2 3 config BUSYBOX_CUSTOM 4 bool "Customize busybox options" 5 default n 6 help 7 Enabling this allows full customization of busybox settings. 8 Note that there are many options here that can result in a build 9 that doesn't work properly. Enabling customization will mark your 10 build as "tainted" for the purpose of bug reports. 11 See the variables written to /etc/openwrt_release 12 13 Unless you know what you are doing, you should leave this as 'n' 14 15 source "Config-defaults.in" 16 17 if BUSYBOX_CUSTOM 18 source "config/Config.in" 19 endif 20 21 endif
可以看到，配置文件Config.in中定义了一个名为BUSYBOX_CUSTOM的配置项。当没有选中该配置项的时候，只导入默认配置文件”Config-default.in”中的配置。当我们选中该配置项的时，就再导入config目录下对应于busybox原生配置项的配置文件，进而允许用户自定义busybox的全部功能。
我们暂且看Config.in文件中自定义配置的内容。此时，Config.in只导入了Config-defaults.in文件中的配置项。打开Config-defaults.in这个文件可以看到，里面定义了一系列以BUSYBOX_DEFAULT开头的配置项。具体的代码如下所示：
1 #
2 # For a description of the syntax of this configuration file,
3 # see docs/Kconfig-language.txt.
4 #
5
6
7 config BUSYBOX_CONFIG_HAVE_DOT_CONFIG
8 bool
9 default BUSYBOX_DEFAULT_HAVE_DOT_CONFIG
10
11 menu "Settings"
12
13 config BUSYBOX_CONFIG_DESKTOP
14 bool "Enable compatibility for full-blown desktop systems (8kb)"
15 default BUSYBOX_DEFAULT_DESKTOP
16 help
17 Enable applet options and features which are not essential.
18 Many applet options have dedicated config options to (de)select them
19 under that applet; this options enables those options which have no
20 individual config item for them.
21
22 Select this if you plan to use busybox on full-blown desktop machine
23 with common Linux distro, which needs higher level of command-line
24 compatibility.
25
26 If you are preparing your build to be used on an embedded box
27 where you have tighter control over the entire set of userspace
28 tools, you can unselect this option for smaller code size.
29
30 config BUSYBOX_CONFIG_EXTRA_COMPAT
31 bool "Provide compatible behavior for rare corner cases (bigger code)"
32 default BUSYBOX_DEFAULT_EXTRA_COMPAT
33 help
34 This option makes grep, sed etc handle rare corner cases
35 (embedded NUL bytes and such). This makes code bigger and uses
36 some GNU extensions in libc. You probably only need this option
37 if you plan to run busybox on desktop.
38
39 config BUSYBOX_CONFIG_FEDORA_COMPAT
40 bool "Building for Fedora distribution"
41 default BUSYBOX_DEFAULT_FEDORA_COMPAT
42 help
43 This option makes some tools behave like they do on Fedora.
44
45 At the time of this writing (2017-08) this only affects uname:
46 normally, uname -p (processor) and uname -i (platform)
47 are shown as "unknown", but with this option uname -p
48 shows the same string as uname -m (machine type),
49 and so does uname -i unless machine type is i486/i586/i686 -
50 then uname -i shows "i386".
51
52 config BUSYBOX_CONFIG_INCLUDE_SUSv2
53 bool "Enable obsolete features removed before SUSv3"
54 default BUSYBOX_DEFAULT_INCLUDE_SUSv2
55 help
56 This option will enable backwards compatibility with SuSv2,
57 specifically, old-style numeric options ('command -1 <file>')
58 will be supported in head, tail, and fold. (Note: should
59 affect renice too.)
60
61 config BUSYBOX_CONFIG_LONG_OPTS
62 bool "Support --long-options"
63 default BUSYBOX_DEFAULT_LONG_OPTS
64 help
65 Enable this if you want busybox applets to use the gnu --long-option
66 style, in addition to single character -a -b -c style options.
67
68 config BUSYBOX_CONFIG_SHOW_USAGE
69 bool "Show applet usage messages"
70 default BUSYBOX_DEFAULT_SHOW_USAGE
71 help
72 Enabling this option, applets will show terse help messages
73 when invoked with wrong arguments.
74 If you do not want to show any (helpful) usage message when
75 issuing wrong command syntax, you can say 'N' here,
76 saving approximately 7k.
77
78 config BUSYBOX_CONFIG_FEATURE_VERBOSE_USAGE
79 bool "Show verbose applet usage messages"
80 default BUSYBOX_DEFAULT_FEATURE_VERBOSE_USAGE
81 depends on BUSYBOX_CONFIG_SHOW_USAGE
82 help
83 All applets will show verbose help messages when invoked with --help.
84 This will add a lot of text to the binary.
85
86 config BUSYBOX_CONFIG_FEATURE_COMPRESS_USAGE
87 bool "Store applet usage messages in compressed form"
88 default BUSYBOX_DEFAULT_FEATURE_COMPRESS_USAGE
89 depends on BUSYBOX_CONFIG_SHOW_USAGE
90 help
91 Store usage messages in .bz2 compressed form, uncompress them
92 on-the-fly when "APPLET --help" is run.
93
94 If you have a really tiny busybox with few applets enabled (and
95 bunzip2 isn't one of them), the overhead of the decompressor might
96 be noticeable. Also, if you run executables directly from ROM
97 and have very little memory, this might not be a win. Otherwise,
98 you probably want this.
99
100 config BUSYBOX_CONFIG_LFS
101 bool
102 default BUSYBOX_DEFAULT_LFS
103 help
104 If you need to work with large files, enable this option.
105 This will have no effect if your kernel or your C
106 library lacks large file support for large files. Some of the
107 programs that can benefit from large file support include dd, gzip,
108 cp, mount, tar.
109
110 config BUSYBOX_CONFIG_PAM
111 bool "Support PAM (Pluggable Authentication Modules)"
112 default BUSYBOX_DEFAULT_PAM
113 help
114 Use PAM in some applets (currently login and httpd) instead
115 of direct access to password database.
116
117 config BUSYBOX_CONFIG_FEATURE_DEVPTS
118 bool "Use the devpts filesystem for Unix98 PTYs"
119 default BUSYBOX_DEFAULT_FEATURE_DEVPTS
120 help
121 Enable if you want to use Unix98 PTY support. If enabled,
122 busybox will use /dev/ptmx for the master side of the pseudoterminal
123 and /dev/pts/<number> for the slave side. Otherwise, BSD style
124 /dev/ttyp<number> will be used. To use this option, you should have
125 devpts mounted.
126
127 config BUSYBOX_CONFIG_FEATURE_UTMP
128 bool "Support utmp file"
129 default BUSYBOX_DEFAULT_FEATURE_UTMP
130 help
131 The file /var/run/utmp is used to track who is currently logged in.
132 With this option on, certain applets (getty, login, telnetd etc)
133 will create and delete entries there.
134 "who" applet requires this option.
135
136 config BUSYBOX_CONFIG_FEATURE_WTMP
137 bool "Support wtmp file"
138 default BUSYBOX_DEFAULT_FEATURE_WTMP
139 depends on BUSYBOX_CONFIG_FEATURE_UTMP
140 help
141 The file /var/run/wtmp is used to track when users have logged into
142 and logged out of the system.
143 With this option on, certain applets (getty, login, telnetd etc)
144 will append new entries there.
145 "last" applet requires this option.
146
147 config BUSYBOX_CONFIG_FEATURE_PIDFILE
148 bool "Support writing pidfiles"
149 default BUSYBOX_DEFAULT_FEATURE_PIDFILE
150 help
151 This option makes some applets (e.g. crond, syslogd, inetd) write
152 a pidfile at the configured PID_FILE_PATH. It has no effect
153 on applets which require pidfiles to run.
154
155 config BUSYBOX_CONFIG_PID_FILE_PATH
156 string "Directory for pidfiles"
157 default BUSYBOX_DEFAULT_PID_FILE_PATH
158 depends on BUSYBOX_CONFIG_FEATURE_PIDFILE || BUSYBOX_CONFIG_FEATURE_CROND_SPECIAL_TIMES
159 help
160 This is the default path where pidfiles are created. Applets which
161 allow you to set the pidfile path on the command line will override
162 this value. The option has no effect on applets that require you to
163 specify a pidfile path. When crond has the 'Support special times'
164 option enabled, the 'crond.reboot' file is also stored here.
165
166 config BUSYBOX_CONFIG_BUSYBOX
167 bool "Include busybox applet"
168 default BUSYBOX_DEFAULT_BUSYBOX
169 help
170 The busybox applet provides general help message and allows
171 the included applets to be listed. It also provides
172 optional --install command to create applet links. If you unselect
173 this option, running busybox without any arguments will give
174 just a cryptic error message:
175
176 $ busybox
177 busybox: applet not found
178
179 Running "busybox APPLET [ARGS...]" will still work, of course.
180
181 config BUSYBOX_CONFIG_FEATURE_SHOW_SCRIPT
182 bool "Support --show SCRIPT"
183 default BUSYBOX_DEFAULT_FEATURE_SHOW_SCRIPT
184 depends on BUSYBOX_CONFIG_BUSYBOX
185
186 config BUSYBOX_CONFIG_FEATURE_INSTALLER
187 bool "Support --install [-s] to install applet links at runtime"
188 default BUSYBOX_DEFAULT_FEATURE_INSTALLER
189 depends on BUSYBOX_CONFIG_BUSYBOX
190 help
191 Enable 'busybox --install [-s]' support. This will allow you to use
192 busybox at runtime to create hard links or symlinks for all the
193 applets that are compiled into busybox.
194
195 config BUSYBOX_CONFIG_INSTALL_NO_USR
196 bool "Don't use /usr"
197 default BUSYBOX_DEFAULT_INSTALL_NO_USR
198 help
199 Disable use of /usr. "busybox --install" and "make install"
200 will install applets only to /bin and /sbin,
201 never to /usr/bin or /usr/sbin.
202
203 config BUSYBOX_CONFIG_FEATURE_SUID
204 bool "Drop SUID state for most applets"
205 default BUSYBOX_DEFAULT_FEATURE_SUID
206 help
207 With this option you can install the busybox binary belonging
208 to root with the suid bit set, enabling some applets to perform
209 root-level operations even when run by ordinary users
210 (for example, mounting of user mounts in fstab needs this).
211
212 With this option enabled, busybox drops privileges for applets
213 that don't need root access, before entering their main() function.
214
215 If you are really paranoid and don't want even initial busybox code
216 to run under root for every applet, build two busybox binaries with
217 different applets in them (and the appropriate symlinks pointing
218 to each binary), and only set the suid bit on the one that needs it.
219
220 Some applets which require root rights (need suid bit on the binary
221 or to be run by root) and will refuse to execute otherwise:
222 crontab, login, passwd, su, vlock, wall.
223
224 The applets which will use root rights if they have them
225 (via suid bit, or because run by root), but would try to work
226 without root right nevertheless:
227 findfs, ping[6], traceroute[6], mount.
228
229 Note that if you DO NOT select this option, but DO make busybox
230 suid root, ALL applets will run under root, which is a huge
231 security hole (think "cp /some/file /etc/passwd").
232
233 config BUSYBOX_CONFIG_FEATURE_SUID_CONFIG
234 bool "Enable SUID configuration via /etc/busybox.conf"
235 default BUSYBOX_DEFAULT_FEATURE_SUID_CONFIG
236 depends on BUSYBOX_CONFIG_FEATURE_SUID
237 help
238 Allow the SUID/SGID state of an applet to be determined at runtime
239 by checking /etc/busybox.conf. (This is sort of a poor man's sudo.)
240 The format of this file is as follows:
241
242 APPLET = [Ssx-][Ssx-][x-] [USER.GROUP]
243
244 s: USER or GROUP is allowed to execute APPLET.
245 APPLET will run under USER or GROUP
246 (regardless of who's running it).
247 S: USER or GROUP is NOT allowed to execute APPLET.
248 APPLET will run under USER or GROUP.
249 This option is not very sensical.
250 x: USER/GROUP/others are allowed to execute APPLET.
251 No UID/GID change will be done when it is run.
252 -: USER/GROUP/others are not allowed to execute APPLET.
253
254 An example might help:
255
256 |[SUID]
257 |su = ssx root.0 # applet su can be run by anyone and runs with
258 | # euid=0,egid=0
259 |su = ssx # exactly the same
260 |
261 |mount = sx- root.disk # applet mount can be run by root and members
262 | # of group disk (but not anyone else)
263 | # and runs with euid=0 (egid is not changed)
264 |
265 |cp = --- # disable applet cp for everyone
266
267 The file has to be owned by user root, group root and has to be
268 writeable only by root:
269 (chown 0.0 /etc/busybox.conf; chmod 600 /etc/busybox.conf)
270 The busybox executable has to be owned by user root, group
271 root and has to be setuid root for this to work:
272 (chown 0.0 /bin/busybox; chmod 4755 /bin/busybox)
273
274 Robert 'sandman' Griebl has more information here:
275 <url: http://www.softforge.de/bb/suid.html >.
276
277 config BUSYBOX_CONFIG_FEATURE_SUID_CONFIG_QUIET
278 bool "Suppress warning message if /etc/busybox.conf is not readable"
279 default BUSYBOX_DEFAULT_FEATURE_SUID_CONFIG_QUIET
280 depends on BUSYBOX_CONFIG_FEATURE_SUID_CONFIG
281 help
282 /etc/busybox.conf should be readable by the user needing the SUID,
283 check this option to avoid users to be notified about missing
284 permissions.
285
286 config BUSYBOX_CONFIG_FEATURE_PREFER_APPLETS
287 bool "exec prefers applets"
288 default BUSYBOX_DEFAULT_FEATURE_PREFER_APPLETS
289 help
290 This is an experimental option which directs applets about to
291 call 'exec' to try and find an applicable busybox applet before
292 searching the PATH. This is typically done by exec'ing
293 /proc/self/exe.
294
295 This may affect shell, find -exec, xargs and similar applets.
296 They will use applets even if /bin/APPLET -> busybox link
297 is missing (or is not a link to busybox). However, this causes
298 problems in chroot jails without mounted /proc and with ps/top
299 (command name can be shown as 'exe' for applets started this way).
300
301 config BUSYBOX_CONFIG_BUSYBOX_EXEC_PATH
302 string "Path to busybox executable"
303 default BUSYBOX_DEFAULT_BUSYBOX_EXEC_PATH
304 help
305 When applets need to run other applets, busybox
306 sometimes needs to exec() itself. When the /proc filesystem is
307 mounted, /proc/self/exe always points to the currently running
308 executable. If you haven't got /proc, set this to wherever you
309 want to run busybox from.
310
311 config BUSYBOX_CONFIG_SELINUX
312 bool "Support NSA Security Enhanced Linux"
313 default BUSYBOX_DEFAULT_SELINUX
314 help
315 Enable support for SELinux in applets ls, ps, and id. Also provide
316 the option of compiling in SELinux applets.
317
318 If you do not have a complete SELinux userland installed, this stuff
319 will not compile. Specifially, libselinux 1.28 or better is
320 directly required by busybox. If the installation is located in a
321 non-standard directory, provide it by invoking make as follows:
322
323 CFLAGS=-I<libselinux-include-path> \
324 LDFLAGS=-L<libselinux-lib-path> \
325 make
326
327 Most people will leave this set to 'N'.
328
329 config BUSYBOX_CONFIG_FEATURE_CLEAN_UP
330 bool "Clean up all memory before exiting (usually not needed)"
331 default BUSYBOX_DEFAULT_FEATURE_CLEAN_UP
332 help
333 As a size optimization, busybox normally exits without explicitly
334 freeing dynamically allocated memory or closing files. This saves
335 space since the OS will clean up for us, but it can confuse debuggers
336 like valgrind, which report tons of memory and resource leaks.
337
338 Don't enable this unless you have a really good reason to clean
339 things up manually.
340
341 config BUSYBOX_CONFIG_FEATURE_SYSLOG_INFO
342 bool "Support LOG_INFO level syslog messages"
343 default BUSYBOX_DEFAULT_FEATURE_SYSLOG_INFO
344 depends on BUSYBOX_CONFIG_FEATURE_SYSLOG
345 help
346 Applets which send their output to syslog use either LOG_INFO or
347 LOG_ERR log levels, but by disabling this option all messages will
348 be logged at the LOG_ERR level, saving just under 200 bytes.
349
350 # These are auto-selected by other options
351
352 config BUSYBOX_CONFIG_FEATURE_SYSLOG
353 bool #No description makes it a hidden option
354 default BUSYBOX_DEFAULT_FEATURE_SYSLOG
355 #help
356 #This option is auto-selected when you select any applet which may
357 #send its output to syslog. You do not need to select it manually.
358
359 comment 'Build Options'
360
361 config BUSYBOX_CONFIG_STATIC
362 bool "Build static binary (no shared libs)"
363 default BUSYBOX_DEFAULT_STATIC
364 help
365 If you want to build a static binary, which does not use
366 or require any shared libraries, enable this option.
367 Static binaries are larger, but do not require functioning
368 dynamic libraries to be present, which is important if used
369 as a system rescue tool.
370
371 config BUSYBOX_CONFIG_PIE
372 bool "Build position independent executable"
373 default BUSYBOX_DEFAULT_PIE
374 depends on !BUSYBOX_CONFIG_STATIC
375 help
376 Hardened code option. PIE binaries are loaded at a different
377 address at each invocation. This has some overhead,
378 particularly on x86-32 which is short on registers.
379
380 Most people will leave this set to 'N'.
381
382 config BUSYBOX_CONFIG_NOMMU
383 bool "Force NOMMU build"
384 default BUSYBOX_DEFAULT_NOMMU
385 help
386 Busybox tries to detect whether architecture it is being
387 built against supports MMU or not. If this detection fails,
388 or if you want to build NOMMU version of busybox for testing,
389 you may force NOMMU build here.
390
391 Most people will leave this set to 'N'.
392
393 # PIE can be made to work with BUILD_LIBBUSYBOX, but currently
394 # build system does not support that
395 config BUSYBOX_CONFIG_BUILD_LIBBUSYBOX
396 bool "Build shared libbusybox"
397 default BUSYBOX_DEFAULT_BUILD_LIBBUSYBOX
398 depends on !BUSYBOX_CONFIG_FEATURE_PREFER_APPLETS && !BUSYBOX_CONFIG_PIE && !BUSYBOX_CONFIG_STATIC
399 help
400 Build a shared library libbusybox.so.N.N.N which contains all
401 busybox code.
402
403 This feature allows every applet to be built as a really tiny
404 separate executable linked against the library:
405 |$ size 0_lib/l*
406 | text data bss dec hex filename
407 | 939 212 28 1179 49b 0_lib/last
408 | 939 212 28 1179 49b 0_lib/less
409 | 919138 8328 1556 929022 e2cfe 0_lib/libbusybox.so.1.N.M
410
411 This is useful on NOMMU systems which are not capable
412 of sharing executables, but are capable of sharing code
413 in dynamic libraries.
414
415 config BUSYBOX_CONFIG_FEATURE_LIBBUSYBOX_STATIC
416 bool "Pull in all external references into libbusybox"
417 default BUSYBOX_DEFAULT_FEATURE_LIBBUSYBOX_STATIC
418 depends on BUSYBOX_CONFIG_BUILD_LIBBUSYBOX
419 help
420 Make libbusybox library independent, not using or requiring
421 any other shared libraries.
422
423 config BUSYBOX_CONFIG_FEATURE_INDIVIDUAL
424 bool "Produce a binary for each applet, linked against libbusybox"
425 default BUSYBOX_DEFAULT_FEATURE_INDIVIDUAL
426 depends on BUSYBOX_CONFIG_BUILD_LIBBUSYBOX
427 help
428 If your CPU architecture doesn't allow for sharing text/rodata
429 sections of running binaries, but allows for runtime dynamic
430 libraries, this option will allow you to reduce memory footprint
431 when you have many different applets running at once.
432
433 If your CPU architecture allows for sharing text/rodata,
434 having single binary is more optimal.
435
436 Each applet will be a tiny program, dynamically linked
437 against libbusybox.so.N.N.N.
438
439 You need to have a working dynamic linker.
440
441 config BUSYBOX_CONFIG_FEATURE_SHARED_BUSYBOX
442 bool "Produce additional busybox binary linked against libbusybox"
443 default BUSYBOX_DEFAULT_FEATURE_SHARED_BUSYBOX
444 depends on BUSYBOX_CONFIG_BUILD_LIBBUSYBOX
445 help
446 Build busybox, dynamically linked against libbusybox.so.N.N.N.
447
448 You need to have a working dynamic linker.
449
450 ### config BUILD_AT_ONCE
451 ### bool "Compile all sources at once"
452 ### default n
453 ### help
454 ### Normally each source-file is compiled with one invocation of
455 ### the compiler.
456 ### If you set this option, all sources are compiled at once.
457 ### This gives the compiler more opportunities to optimize which can
458 ### result in smaller and/or faster binaries.
459 ###
460 ### Setting this option will consume alot of memory, e.g. if you
461 ### enable all applets with all features, gcc uses more than 300MB
462 ### RAM during compilation of busybox.
463 ###
464 ### This option is most likely only beneficial for newer compilers
465 ### such as gcc-4.1 and above.
466 ###
467 ### Say 'N' unless you know what you are doing.
468
469 config BUSYBOX_CONFIG_CROSS_COMPILER_PREFIX
470 string "Cross compiler prefix"
471 default BUSYBOX_DEFAULT_CROSS_COMPILER_PREFIX
472 help
473 If you want to build busybox with a cross compiler, then you
474 will need to set this to the cross-compiler prefix, for example,
475 "i386-uclibc-".
476
477 Note that CROSS_COMPILE environment variable or
478 "make CROSS_COMPILE=xxx ..." will override this selection.
479
480 Native builds leave this empty.
481
482 config BUSYBOX_CONFIG_SYSROOT
483 string "Path to sysroot"
484 default BUSYBOX_DEFAULT_SYSROOT
485 help
486 If you want to build busybox with a cross compiler, then you
487 might also need to specify where /usr/include and /usr/lib
488 will be found.
489
490 For example, busybox can be built against an installed
491 Android NDK, platform version 9, for ARM ABI with
492
493 CONFIG_SYSROOT=/opt/android-ndk/platforms/android-9/arch-arm
494
495 Native builds leave this empty.
496
497 config BUSYBOX_CONFIG_EXTRA_CFLAGS
498 string "Additional CFLAGS"
499 default BUSYBOX_DEFAULT_EXTRA_CFLAGS
500 help
501 Additional CFLAGS to pass to the compiler verbatim.
502
503 config BUSYBOX_CONFIG_EXTRA_LDFLAGS
504 string "Additional LDFLAGS"
505 default BUSYBOX_DEFAULT_EXTRA_LDFLAGS
506 help
507 Additional LDFLAGS to pass to the linker verbatim.
508
509 config BUSYBOX_CONFIG_EXTRA_LDLIBS
510 string "Additional LDLIBS"
511 default BUSYBOX_DEFAULT_EXTRA_LDLIBS
512 help
513 Additional LDLIBS to pass to the linker with -l.
514
515 config BUSYBOX_CONFIG_USE_PORTABLE_CODE
516 bool "Avoid using GCC-specific code constructs"
517 default BUSYBOX_DEFAULT_USE_PORTABLE_CODE
518 help
519 Use this option if you are trying to compile busybox with
520 compiler other than gcc.
521 If you do use gcc, this option may needlessly increase code size.
522
523 config BUSYBOX_CONFIG_STACK_OPTIMIZATION_386
524 bool "Use -mpreferred-stack-boundary=2 on i386 arch"
525 default BUSYBOX_DEFAULT_STACK_OPTIMIZATION_386
526 help
527 This option makes for smaller code, but some libc versions
528 do not work with it (they use SSE instructions without
529 ensuring stack alignment).
530
531 config BUSYBOX_CONFIG_STATIC_LIBGCC
532 bool "Use -static-libgcc"
533 default BUSYBOX_DEFAULT_STATIC_LIBGCC
534 help
535 This option instructs gcc to link in a static version of its
536 support library, libgcc. This means that the binary will require
537 one fewer dynamic library at run time.
538
539 comment 'Installation Options ("make install" behavior)'
540
541 choice
542 prompt "What kind of applet links to install"
543 default BUSYBOX_CONFIG_INSTALL_APPLET_SYMLINKS
544 help
545 Choose what kind of links to applets are created by "make install".
546
547 config BUSYBOX_CONFIG_INSTALL_APPLET_SYMLINKS
548 bool "as soft-links"
549 help
550 Install applets as soft-links to the busybox binary. This needs some
551 free inodes on the filesystem, but might help with filesystem
552 generators that can't cope with hard-links.
553
554 config BUSYBOX_CONFIG_INSTALL_APPLET_HARDLINKS
555 bool "as hard-links"
556 help
557 Install applets as hard-links to the busybox binary. This might
558 count on a filesystem with few inodes.
559
560 config BUSYBOX_CONFIG_INSTALL_APPLET_SCRIPT_WRAPPERS
561 bool "as script wrappers"
562 help
563 Install applets as script wrappers that call the busybox binary.
564
565 config BUSYBOX_CONFIG_INSTALL_APPLET_DONT
566 bool "not installed"
567 help
568 Do not install applet links. Useful when you plan to use
569 busybox --install for installing links, or plan to use
570 a standalone shell and thus don't need applet links.
571
572 endchoice
573
574 choice
575 prompt "/bin/sh applet link"
576 default BUSYBOX_CONFIG_INSTALL_SH_APPLET_SYMLINK
577 depends on BUSYBOX_CONFIG_INSTALL_APPLET_SCRIPT_WRAPPERS
578 help
579 Choose how you install /bin/sh applet link.
580
581 config BUSYBOX_CONFIG_INSTALL_SH_APPLET_SYMLINK
582 bool "as soft-link"
583 help
584 Install /bin/sh applet as soft-link to the busybox binary.
585
586 config BUSYBOX_CONFIG_INSTALL_SH_APPLET_HARDLINK
587 bool "as hard-link"
588 help
589 Install /bin/sh applet as hard-link to the busybox binary.
590
591 config BUSYBOX_CONFIG_INSTALL_SH_APPLET_SCRIPT_WRAPPER
592 bool "as script wrapper"
593 help
594 Install /bin/sh applet as script wrapper that calls
595 the busybox binary.
596
597 endchoice
598
599 config BUSYBOX_CONFIG_PREFIX
600 string "Destination path for 'make install'"
601 default BUSYBOX_DEFAULT_PREFIX
602 help
603 Where "make install" should install busybox binary and links.
604
605 comment 'Debugging Options'
606
607 config BUSYBOX_CONFIG_DEBUG
608 bool "Build with debug information"
609 default BUSYBOX_DEFAULT_DEBUG
610 help
611 Say Y here to compile with debug information.
612 This increases the size of the binary considerably, and
613 should only be used when doing development.
614
615 This adds -g option to gcc command line.
616
617 Most people should answer N.
618
619 config BUSYBOX_CONFIG_DEBUG_PESSIMIZE
620 bool "Disable compiler optimizations"
621 default BUSYBOX_DEFAULT_DEBUG_PESSIMIZE
622 depends on BUSYBOX_CONFIG_DEBUG
623 help
624 The compiler's optimization of source code can eliminate and reorder
625 code, resulting in an executable that's hard to understand when
626 stepping through it with a debugger. This switches it off, resulting
627 in a much bigger executable that more closely matches the source
628 code.
629
630 This replaces -Os/-O2 with -O0 in gcc command line.
631
632 config BUSYBOX_CONFIG_DEBUG_SANITIZE
633 bool "Enable runtime sanitizers (ASAN/LSAN/USAN/etc...)"
634 default BUSYBOX_DEFAULT_DEBUG_SANITIZE
635 help
636 Say Y here if you want to enable runtime sanitizers. These help
637 catch bad memory accesses (e.g. buffer overflows), but will make
638 the executable larger and slow down runtime a bit.
639
640 This adds -fsanitize=foo options to gcc command line.
641
642 If you aren't developing/testing busybox, say N here.
643
644 config BUSYBOX_CONFIG_UNIT_TEST
645 bool "Build unit tests"
646 default BUSYBOX_DEFAULT_UNIT_TEST
647 help
648 Say Y here if you want to build unit tests (both the framework and
649 test cases) as an applet. This results in bigger code, so you
650 probably don't want this option in production builds.
651
652 config BUSYBOX_CONFIG_WERROR
653 bool "Abort compilation on any warning"
654 default BUSYBOX_DEFAULT_WERROR
655 help
656 This adds -Werror to gcc command line.
657
658 Most people should answer N.
659
660 config BUSYBOX_CONFIG_WARN_SIMPLE_MSG
661 bool "Warn about single parameter bb_xx_msg calls"
662 default BUSYBOX_DEFAULT_WARN_SIMPLE_MSG
663 help
664 This will cause warnings to be shown for any instances of
665 bb_error_msg(), bb_error_msg_and_die(), bb_perror_msg(),
666 bb_perror_msg_and_die(), bb_herror_msg() or bb_herror_msg_and_die()
667 being called with a single parameter. In these cases the equivalent
668 bb_simple_xx_msg function should be used instead.
669 Note that use of STRERROR_FMT may give false positives.
670
671 If you aren't developing busybox, say N here.
672
673 choice
674 prompt "Additional debugging library"
675 default BUSYBOX_CONFIG_NO_DEBUG_LIB
676 help
677 Using an additional debugging library will make busybox become
678 considerably larger and will cause it to run more slowly. You
679 should always leave this option disabled for production use.
680
681 dmalloc support:
682 ----------------
683 This enables compiling with dmalloc ( http://dmalloc.com/ )
684 which is an excellent public domain mem leak and malloc problem
685 detector. To enable dmalloc, before running busybox you will
686 want to properly set your environment, for example:
687 export DMALLOC_OPTIONS=debug=0x34f47d83,inter=100,log=logfile
688 The 'debug=' value is generated using the following command
689 dmalloc -p log-stats -p log-non-free -p log-bad-space \
690 -p log-elapsed-time -p check-fence -p check-heap \
691 -p check-lists -p check-blank -p check-funcs -p realloc-copy \
692 -p allow-free-null
693
694 Electric-fence support:
695 -----------------------
696 This enables compiling with Electric-fence support. Electric
697 fence is another very useful malloc debugging library which uses
698 your computer's virtual memory hardware to detect illegal memory
699 accesses. This support will make busybox be considerably larger
700 and run slower, so you should leave this option disabled unless
701 you are hunting a hard to find memory problem.
702
703
704 config BUSYBOX_CONFIG_NO_DEBUG_LIB
705 bool "None"
706
707 config BUSYBOX_CONFIG_DMALLOC
708 bool "Dmalloc"
709
710 config BUSYBOX_CONFIG_EFENCE
711 bool "Electric-fence"
712
713 endchoice
714
715 source "libbb/Config.in"
716
717 endmenu
718
719 comment "Applets"
720
721 source "archival/Config.in"
722 source "coreutils/Config.in"
723 source "console-tools/Config.in"
724 source "debianutils/Config.in"
725 source "klibc-utils/Config.in"
726 source "editors/Config.in"
727 source "findutils/Config.in"
728 source "init/Config.in"
729 source "loginutils/Config.in"
730 source "e2fsprogs/Config.in"
731 source "modutils/Config.in"
732 source "util-linux/Config.in"
733 source "miscutils/Config.in"
734 source "networking/Config.in"
735 source "printutils/Config.in"
736 source "mailutils/Config.in"
737 source "procps/Config.in"
738 source "runit/Config.in"
739 source "selinux/Config.in"
740 source "shell/Config.in"
741 source "sysklogd/Config.in"其实，这些配置项就是busybox原本对应的所有配置项。只是名字不同而已。最后，在Makefile中会将这些配置项转换为busybox本身的配置文件。openwrt/package/utils/busybox/Makefile代码如下所示：
120 define Build/Configure 121 rm -f $(PKG_BUILD_DIR)/.config 122 touch $(PKG_BUILD_DIR)/.config 123 ifeq ($(DEVICE_TYPE),nas) 124 echo "CONFIG_HDPARM=y" >> $(PKG_BUILD_DIR)/.config 125 endif 126 ifeq ($(BUILD_VARIANT),selinux) 127 cat $(TOPDIR)/$(SOURCE)/selinux.config >> $(PKG_BUILD_DIR)/.config 128 endif 129 grep 'CONFIG_BUSYBOX_$(BUSYBOX_SYM)' $(TOPDIR)/.config | sed -e "s,\\(# \)\\?CONFIG_BUSYBOX_$(BUSYBOX_SYM)_\\(.*\\),\\1CONFIG_\\2,g" >> $(PKG_BUILD_DIR)/.config 130 yes 'n' | $(MAKE) -C $(PKG_BUILD_DIR) $(MAKE_FLAGS) oldconfig 131 endef
其中，$(BUSYBOX_SYM)这个变量也是在Makefile中赋值的。这个变量被定义在openwrt/package/utils/busybox/Makefile文件的第25行中，具体如下所示：
25 BUSYBOX_SYM=$(if $(CONFIG_BUSYBOX_CUSTOM),CONFIG,DEFAULT)
这样一来我们就清楚了。在busybox的Makefile中，未选中CONFIG_BUSYBOX_CUSTOM的情况下，BUSYBOX_SYM的值为DEFAULT，则将CONFIG_BUSYBOX_DEFAULT_xxx筛选出来，处理为busybox最终的配置项，而这些CONFIG_BUSYBOX_DEFAULT_xxx是在Config-defaults.in文件中配置好的。
在选中了CONFIG_BUSYBOX_CUSTOM的情况下，则最终将CONFIG_BUSYBOX_CONFIG_xxx筛选出来使用。
接下来，我们就来看一下自定义的情况。自定义的情况其实也很清晰，就是引入了config目录下的配置项。这些配置项，跟busybox源码中的布局和内容完全一致，区别只是配置项的名字均以BUSYBOX_CONFIG开头，且默认值均为对应的以BUSYBOX_DEFAULT_开头的配置项。而这些BUSYBOX_DEFAULT_开头的配置项都是在Config-default.in中配置的。例如
openwrt/package/utils/busybox/config/init/Config.in文件中的例子：
1 # DO NOT EDIT. This file is generated from Config.src 2 # 3 # For a description of the syntax of this configuration file, 4 # see docs/Kconfig-language.txt. 5 # 6 7 menu "Init Utilities" 8 9 config BUSYBOX_CONFIG_BOOTCHARTD 10 bool "bootchartd (10 kb)" 11 default BUSYBOX_DEFAULT_BOOTCHARTD 12 help 13 bootchartd is commonly used to profile the boot process 14 for the purpose of speeding it up. In this case, it is started 15 by the kernel as the init process. This is configured by adding 16 the init=/sbin/bootchartd option to the kernel command line. 17 18 It can also be used to monitor the resource usage of a specific 19 application or the running system in general. In this case, 20 bootchartd is started interactively by running bootchartd start 21 and stopped using bootchartd stop. 22 23 config BUSYBOX_CONFIG_FEATURE_BOOTCHARTD_BLOATED_HEADER 24 bool "Compatible, bloated header" 25 default BUSYBOX_DEFAULT_FEATURE_BOOTCHARTD_BLOATED_HEADER 26 depends on BUSYBOX_CONFIG_BOOTCHARTD 27 help 28 Create extended header file compatible with "big" bootchartd. 29 "Big" bootchartd is a shell script and it dumps some 30 "convenient" info into the header, such as: 31 title = Boot chart for `hostname` (`date`) 32 system.uname = `uname -srvm` 33 system.release = `cat /etc/DISTRO-release` 34 system.cpu = `grep '^model name' /proc/cpuinfo | head -1` ($cpucount) 35 system.kernel.options = `cat /proc/cmdline` 36 This data is not mandatory for bootchart graph generation, 37 and is considered bloat. Nevertheless, this option 38 makes bootchartd applet to dump a subset of it. 39 40 config BUSYBOX_CONFIG_FEATURE_BOOTCHARTD_CONFIG_FILE 41 bool "Support bootchartd.conf" 42 default BUSYBOX_DEFAULT_FEATURE_BOOTCHARTD_CONFIG_FILE 43 depends on BUSYBOX_CONFIG_BOOTCHARTD 44 help 45 Enable reading and parsing of $PWD/bootchartd.conf 46 and /etc/bootchartd.conf files. 47 config BUSYBOX_CONFIG_HALT 48 bool "halt (4 kb)" 49 default BUSYBOX_DEFAULT_HALT 50 help 51 Stop all processes and halt the system. 52 53 config BUSYBOX_CONFIG_POWEROFF 54 bool "poweroff (4 kb)" 55 default BUSYBOX_DEFAULT_POWEROFF 56 help 57 Stop all processes and power off the system. 58 59 config BUSYBOX_CONFIG_REBOOT 60 bool "reboot (4 kb)" 61 default BUSYBOX_DEFAULT_REBOOT 62 help 63 Stop all processes and reboot the system. 64 65 config BUSYBOX_CONFIG_FEATURE_WAIT_FOR_INIT 66 bool "Before signaling init, make sure it is ready for it" 67 default BUSYBOX_DEFAULT_FEATURE_WAIT_FOR_INIT 68 depends on BUSYBOX_CONFIG_HALT || BUSYBOX_CONFIG_POWEROFF || BUSYBOX_CONFIG_REBOOT 69 help 70 In rare cases, poweroff may be commanded by firmware to OS 71 even before init process exists. On Linux, this spawns 72 "/sbin/poweroff" very early. This option adds code 73 which checks that init is ready to receive poweroff 74 commands. Code size increase of ~80 bytes. 75 76 config BUSYBOX_CONFIG_FEATURE_CALL_TELINIT 77 bool "Call telinit on shutdown and reboot" 78 default BUSYBOX_DEFAULT_FEATURE_CALL_TELINIT 79 depends on (BUSYBOX_CONFIG_HALT || BUSYBOX_CONFIG_POWEROFF || BUSYBOX_CONFIG_REBOOT) && !BUSYBOX_CONFIG_INIT 80 help 81 Call an external program (normally telinit) to facilitate 82 a switch to a proper runlevel. 83 84 This option is only available if you selected halt and friends, 85 but did not select init. 86 87 config BUSYBOX_CONFIG_TELINIT_PATH 88 string "Path to telinit executable" 89 default BUSYBOX_DEFAULT_TELINIT_PATH 90 depends on BUSYBOX_CONFIG_FEATURE_CALL_TELINIT 91 help 92 When busybox halt and friends have to call external telinit 93 to facilitate proper shutdown, this path is to be used when 94 locating telinit executable. 95 config BUSYBOX_CONFIG_INIT 96 bool "init (10 kb)" 97 default BUSYBOX_DEFAULT_INIT 98 select BUSYBOX_CONFIG_FEATURE_SYSLOG 99 help 100 init is the first program run when the system boots. 101 102 config BUSYBOX_CONFIG_LINUXRC 103 bool "linuxrc: support running init from initrd (not initramfs)" 104 default BUSYBOX_DEFAULT_LINUXRC 105 select BUSYBOX_CONFIG_FEATURE_SYSLOG 106 help 107 Legacy support for running init under the old-style initrd. Allows 108 the name linuxrc to act as init, and it doesn't assume init is PID 1. 109 110 This does not apply to initramfs, which runs /init as PID 1 and 111 requires no special support. 112 113 config BUSYBOX_CONFIG_FEATURE_USE_INITTAB 114 bool "Support reading an inittab file" 115 default BUSYBOX_DEFAULT_FEATURE_USE_INITTAB 116 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 117 help 118 Allow init to read an inittab file when the system boot. 119 120 config BUSYBOX_CONFIG_FEATURE_KILL_REMOVED 121 bool "Support killing processes that have been removed from inittab" 122 default BUSYBOX_DEFAULT_FEATURE_KILL_REMOVED 123 depends on BUSYBOX_CONFIG_FEATURE_USE_INITTAB 124 help 125 When respawn entries are removed from inittab and a SIGHUP is 126 sent to init, this option will make init kill the processes 127 that have been removed. 128 129 config BUSYBOX_CONFIG_FEATURE_KILL_DELAY 130 int "How long to wait between TERM and KILL (0 - send TERM only)" if FEATURE_KILL_REMOVED 131 range 0 1024 132 default BUSYBOX_DEFAULT_FEATURE_KILL_DELAY 133 depends on BUSYBOX_CONFIG_FEATURE_KILL_REMOVED 134 help 135 With nonzero setting, init sends TERM, forks, child waits N 136 seconds, sends KILL and exits. Setting it too high is unwise 137 (child will hang around for too long and could actually kill 138 the wrong process!) 139 140 config BUSYBOX_CONFIG_FEATURE_INIT_SCTTY 141 bool "Run commands with leading dash with controlling tty" 142 default BUSYBOX_DEFAULT_FEATURE_INIT_SCTTY 143 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 144 help 145 If this option is enabled, init will try to give a controlling 146 tty to any command which has leading hyphen (often it's "-/bin/sh"). 147 More precisely, init will do "ioctl(STDIN_FILENO, TIOCSCTTY, 0)". 148 If device attached to STDIN_FILENO can be a ctty but is not yet 149 a ctty for other session, it will become this process' ctty. 150 This is not the traditional init behavour, but is often what you want 151 in an embedded system where the console is only accessed during 152 development or for maintenance. 153 NB: using cttyhack applet may work better. 154 155 config BUSYBOX_CONFIG_FEATURE_INIT_SYSLOG 156 bool "Enable init to write to syslog" 157 default BUSYBOX_DEFAULT_FEATURE_INIT_SYSLOG 158 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 159 help 160 If selected, some init messages are sent to syslog. 161 Otherwise, they are sent to VT #5 if linux virtual tty is detected 162 (if not, no separate logging is done). 163 164 config BUSYBOX_CONFIG_FEATURE_INIT_QUIET 165 bool "Be quiet on boot (no 'init started:' message)" 166 default BUSYBOX_DEFAULT_FEATURE_INIT_QUIET 167 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 168 169 config BUSYBOX_CONFIG_FEATURE_INIT_COREDUMPS 170 bool "Support dumping core for child processes (debugging only)" 171 default BUSYBOX_DEFAULT_FEATURE_INIT_COREDUMPS # not Y because this is a debug option 172 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 173 help 174 If this option is enabled and the file /.init_enable_core 175 exists, then init will call setrlimit() to allow unlimited 176 core file sizes. If this option is disabled, processes 177 will not generate any core files. 178 179 config BUSYBOX_CONFIG_INIT_TERMINAL_TYPE 180 string "Initial terminal type" 181 default BUSYBOX_DEFAULT_INIT_TERMINAL_TYPE 182 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 183 help 184 This is the initial value set by init for the TERM environment 185 variable. This variable is used by programs which make use of 186 extended terminal capabilities. 187 188 Note that on Linux, init attempts to detect serial terminal and 189 sets TERM to "vt102" if one is found. 190 191 config BUSYBOX_CONFIG_FEATURE_INIT_MODIFY_CMDLINE 192 bool "Clear init's command line" 193 default BUSYBOX_DEFAULT_FEATURE_INIT_MODIFY_CMDLINE 194 depends on BUSYBOX_CONFIG_INIT || BUSYBOX_CONFIG_LINUXRC 195 help 196 When launched as PID 1 and after parsing its arguments, init 197 wipes all the arguments but argv[0] and rewrites argv[0] to 198 contain only "init", so that its command line appears solely as 199 "init" in tools such as ps. 200 If this option is set to Y, init will keep its original behavior, 201 otherwise, all the arguments including argv[0] will be preserved, 202 be they parsed or ignored by init. 203 The original command-line used to launch init can then be 204 retrieved in /proc/1/cmdline on Linux, for example. 205 206 endmenu
也就是说，当用户需要自定义的时候引入了BUSYBOX_CONFIG_xxx的配置项。但是，其默认值还是用以前已经配置好的。此时，要自定义的话就在这个基础上进行修改即可。
最终用户的配置就体现在BUSYBOX_CONFIG_xxx的配置项上。如前面介绍的那样，在选中了CONFIG_BUSYBOX_CUSTOM的情况下，BUSYBOX_SYM的值为CONFIG，则将CONFIG_BUSYBOX_CONFIG_xxx筛选出来，处理为busybox最终的配置项。
3、配置项文件的生成
搞清楚了如何集成之后，接下来的问题就是，这些BUSYBOX_DEFAULT_xxx 和 BUSYBOX_CONFIG_xxx 的配置文件，是怎么来的，如此多的配置项，肯定不可能时手工修改的，必然有自动化处理。
是的，这些BUSYBOX_CONFIG_xxx配置项，就是从busybox本身的配置项生成而来。而这些BUSYBOX_DEFAULT_xxx的默认配置值，其实就是从一份配置好的busybox.config文件生成而来。在busybox的包中，就提供了两个脚本
convert_defaults.pl 和 convert_menuconfig.pl，用来生成配置项和默认配置值
4、使软件包随配置项改变而重新编译
一般软件包在编译过一次之后，如果源码没有改动，则下次make无须重新编译。
但对于busybox这种包，源码未变，配置改变了的话，也是需要重新编译的。现在的问题在于，用户修改配置项，是在openwrt的.config修改，根本不会改动到busybox这个目录下的文件。
那么busybox包就需要有一个方法，来监控配置项的变动。如果配置项变化，则需要重新编译。如何监控呢？从makefile中也可以找到答案，正如openwrt/package/utils/busybox/Makefile文件中如下代码那样。
34 ifeq ($(DUMP),) 35 STAMP_CONFIGURED:=$(strip $(STAMP_CONFIGURED))_$(shell grep '^CONFIG_BUSYBOX_' $(TOPDIR)/.config | $(MKHASH) md5) 36 endif
此处设置了STAMP_CONFIGURED变量，这个变量的值，是将.config中所有CONFIG_BUSYBOX_滤出，再做md5得到的值。一旦这些配置项发生变化，则md5的值会改变，STAMP_CONFIGURED的值也会改变。编译包的时候，就能判断出需要重新编译。
具体的，STAMP_CONFIGURED值是在package.mk中使用。这里还有其他的类似变量，只要改变了，就说明需要重新执行对应的操作。如STAMP_CONFIGURED，STAMP_BUILT，STAMP_INSTALLED等。
这个配置项，也会在软件包的编译目录体现出来。如果没有对其赋值，则在编译目录下，可看到名字类似 .configured_yyy 的隐藏文件。
对其进行赋值之后，这个文件的形式会变成 .configured_yyy_622f380fff06dde988852308f044653b 这种形式，后面跟着的就是由配置项生产的md5值。
5、总结
弄清楚OpenWRT集成busybox配置的套路之后，修改一下convert_defaults.pl 和 convert_menuconfig.pl文件，就可以套用到其他软件包上了。
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