init.rc文件的分析

init.rc文件有两份，一个对应于normal mode，一个是recovery mode.分别对应如下文件：

• normal mode: ./system/core/rootdir/init.rc
• recovery mode: ./bootable/recovery/etc/init.rc

init.rc文件的语法&作用，定义在./system/core/init/readme.txt。为阅读方便，拷贝如下：

Android Init Language---------------------The Android Init Language consists of four broad classes of statements,which are Actions, Commands, Services, and Options.All of these are line-oriented, consisting of tokens separated bywhitespace.  The c-style backslash escapes may be used to insertwhitespace into a token.  Double quotes may also be used to preventwhitespace from breaking text into multiple tokens.  The backslash,when it is the last character on a line, may be used for line-folding.Lines which start with a # (leading whitespace allowed) are comments.Actions and Services implicitly declare a new section.  All commandsor options belong to the section most recently declared.  Commandsor options before the first section are ignored.Actions and Services have unique names.  If a second Action or Serviceis declared with the same name as an existing one, it is ignored asan error.  (??? should we override instead)Actions-------Actions are named sequences of commands.  Actions have a trigger whichis used to determine when the action should occur.  When an eventoccurs which matches an action's trigger, that action is added tothe tail of a to-be-executed queue (unless it is already on thequeue).Each action in the queue is dequeued in sequence and each command inthat action is executed in sequence.  Init handles other activities(device creation/destruction, property setting, process restarting)"between" the execution of the commands in activities.Actions take the form of:on <trigger>   <command>   <command>   <command>Services--------Services are programs which init launches and (optionally) restartswhen they exit.  Services take the form of:service <name> <pathname> [ <argument> ]*   <option>   <option>   ...Options-------Options are modifiers to services.  They affect how and when initruns the service.critical   This is a device-critical service. If it exits more than four times in   four minutes, the device will reboot into recovery mode.disabled   This service will not automatically start with its class.   It must be explicitly started by name.setenv <name> <value>   Set the environment variable <name> to <value> in the launched process.socket <name> <type> <perm> [ <user> [ <group> [ <context> ] ] ]   Create a unix domain socket named /dev/socket/<name> and pass   its fd to the launched process.  <type> must be "dgram", "stream" or "seqpacket".   User and group default to 0.   Context is the SELinux security context for the socket.   It defaults to the service security context, as specified by seclabel or   computed based on the service executable file security context.user <username>   Change to username before exec'ing this service.   Currently defaults to root.  (??? probably should default to nobody)   Currently, if your process requires linux capabilities then you cannot use   this command. You must instead request the capabilities in-process while   still root, and then drop to your desired uid.group <groupname> [ <groupname> ]*   Change to groupname before exec'ing this service.  Additional   groupnames beyond the (required) first one are used to set the   supplemental groups of the process (via setgroups()).   Currently defaults to root.  (??? probably should default to nobody)seclabel <securitycontext>  Change to securitycontext before exec'ing this service.  Primarily for use by services run from the rootfs, e.g. ueventd, adbd.  Services on the system partition can instead use policy-defined transitions  based on their file security context.  If not specified and no transition is defined in policy, defaults to the init context.oneshot   Do not restart the service when it exits.class <name>   Specify a class name for the service.  All services in a   named class may be started or stopped together.  A service   is in the class "default" if one is not specified via the   class option.onrestart    Execute a Command (see below) when service restarts.Triggers--------   Triggers are strings which can be used to match certain kinds   of events and used to cause an action to occur.boot   This is the first trigger that will occur when init starts   (after /init.conf is loaded)<name>=<value>   Triggers of this form occur when the property <name> is set   to the specific value <value>.device-added-<path>device-removed-<path>   Triggers of these forms occur when a device node is added   or removed.service-exited-<name>   Triggers of this form occur when the specified service exits.Commands--------exec <path> [ <argument> ]*   Fork and execute a program (<path>).  This will block until   the program completes execution.  It is best to avoid exec   as unlike the builtin commands, it runs the risk of getting   init "stuck". (??? maybe there should be a timeout?)export <name> <value>   Set the environment variable <name> equal to <value> in the   global environment (which will be inherited by all processes   started after this command is executed)ifup <interface>   Bring the network interface <interface> online.import <filename>   Parse an init config file, extending the current configuration.hostname <name>   Set the host name.chdir <directory>   Change working directory.chmod <octal-mode> <path>   Change file access permissions.chown <owner> <group> <path>   Change file owner and group.chroot <directory>  Change process root directory.class_start <serviceclass>   Start all services of the specified class if they are   not already running.class_stop <serviceclass>   Stop all services of the specified class if they are   currently running.domainname <name>   Set the domain name.insmod <path>   Install the module at <path>mkdir <path> [mode] [owner] [group]   Create a directory at <path>, optionally with the given mode, owner, and   group. If not provided, the directory is created with permissions 755 and   owned by the root user and root group.mount <type> <device> <dir> [ <mountoption> ]*   Attempt to mount the named device at the directory <dir>   <device> may be of the form mtd@name to specify a mtd block   device by name.   <mountoption>s include "ro", "rw", "remount", "noatime", ...restorecon <path> [ <path> ]*   Restore the file named by <path> to the security context specified   in the file_contexts configuration.   Not required for directories created by the init.rc as these are   automatically labeled correctly by init.restorecon_recursive <path> [ <path> ]*   Recursively restore the directory tree named by <path> to the   security contexts specified in the file_contexts configuration.   Do NOT use this with paths leading to shell-writable or app-writable   directories, e.g. /data/local/tmp, /data/data or any prefix thereof.setcon <securitycontext>   Set the current process security context to the specified string.   This is typically only used from early-init to set the init context   before any other process is started.setenforce 0|1   Set the SELinux system-wide enforcing status.   0 is permissive (i.e. log but do not deny), 1 is enforcing.setkey   TBDsetprop <name> <value>   Set system property <name> to <value>.setrlimit <resource> <cur> <max>   Set the rlimit for a resource.setsebool <name> <value>   Set SELinux boolean <name> to <value>.   <value> may be 1|true|on or 0|false|offstart <service>   Start a service running if it is not already running.stop <service>   Stop a service from running if it is currently running.symlink <target> <path>   Create a symbolic link at <path> with the value <target>sysclktz <mins_west_of_gmt>   Set the system clock base (0 if system clock ticks in GMT)trigger <event>   Trigger an event.  Used to queue an action from another   action.wait <path> [ <timeout> ]  Poll for the existence of the given file and return when found,  or the timeout has been reached. If timeout is not specified it  currently defaults to five seconds.write <path> <string> [ <string> ]*   Open the file at <path> and write one or more strings   to it with write(2)Properties----------Init updates some system properties to provide some insight intowhat it's doing:init.action    Equal to the name of the action currently being executed or "" if noneinit.command   Equal to the command being executed or "" if none.init.svc.<name>   State of a named service ("stopped", "running", "restarting")Example init.conf-----------------# not complete -- just providing some examples of usage#on boot   export PATH /sbin:/system/sbin:/system/bin   export LD_LIBRARY_PATH /system/lib   mkdir /dev   mkdir /proc   mkdir /sys   mount tmpfs tmpfs /dev   mkdir /dev/pts   mkdir /dev/socket   mount devpts devpts /dev/pts   mount proc proc /proc   mount sysfs sysfs /sys   write /proc/cpu/alignment 4   ifup lo   hostname localhost   domainname localhost   mount yaffs2 mtd@system /system   mount yaffs2 mtd@userdata /data   import /system/etc/init.conf   class_start defaultservice adbd /sbin/adbd   user adb   group adbservice usbd /system/bin/usbd -r   user usbd   group usbd   socket usbd 666service zygote /system/bin/app_process -Xzygote /system/bin --zygote   socket zygote 666service runtime /system/bin/runtime   user system   group systemon device-added-/dev/compass   start akmdon device-removed-/dev/compass   stop akmdservice akmd /sbin/akmd   disabled   user akmd   group akmdDebugging notes---------------By default, programs executed by init will drop stdout and stderr into/dev/null. To help with debugging, you can execute your program via theAndoird program logwrapper. This will redirect stdout/stderr into theAndroid logging system (accessed via logcat).For exampleservice akmd /system/bin/logwrapper /sbin/akmd

从顶层来讲，可以认为init.rc包括两种：action & service. 其中action的语法如下：

on <trigger>   <command>   <command>   <command>

即当某个触发条件(trigger)发生的时候，这个action就执行一系列的command.

service的语法是：

service <name> <pathname> [ <argument> ]*   <option>   <option>   ...

每个服务有个名字(name)，以及该服务对应的程序（pathname, 二进制可执行程序或者shell脚本等）；此外，可以给这个程序传入参数(argument).

service包括一系列的option，用于规定service的执行规则等。

init进程在解析init.rc的时候，会主动去启动这些服务；如：

service flash_recovery /system/etc/install-recovery.sh    class main    oneshot

或者在在action中引用它，如：

# adbd is controlled via property triggers in init.<platform>.usb.rcservice adbd /sbin/adbd --root_seclabel=u:r:su:s0    class core    socket adbd stream 660 system system    disabled    seclabel u:r:adbd:s0# adbd on at boot in emulatoron property:ro.kernel.qemu=1    start adbd

或

service console /system/bin/sh    class core    console    disabled    user shell    group log    seclabel u:r:shell:s0on property:ro.debuggable=1    start console

init.rc中可以使用的command，定义在./system/core/init/keyword.h中，如下：

#ifndef KEYWORDint do_chroot(int nargs, char **args);int do_chdir(int nargs, char **args);int do_class_start(int nargs, char **args);int do_class_stop(int nargs, char **args);int do_class_reset(int nargs, char **args);int do_domainname(int nargs, char **args);int do_exec(int nargs, char **args);int do_export(int nargs, char **args);int do_hostname(int nargs, char **args);int do_ifup(int nargs, char **args);int do_insmod(int nargs, char **args);int do_mkdir(int nargs, char **args);int do_mount_all(int nargs, char **args);int do_mount(int nargs, char **args);int do_powerctl(int nargs, char **args);int do_restart(int nargs, char **args);int do_restorecon(int nargs, char **args);int do_restorecon_recursive(int nargs, char **args);int do_rm(int nargs, char **args);int do_rmdir(int nargs, char **args);int do_setcon(int nargs, char **args);int do_setenforce(int nargs, char **args);int do_setkey(int nargs, char **args);int do_setprop(int nargs, char **args);int do_setrlimit(int nargs, char **args);int do_setsebool(int nargs, char **args);int do_start(int nargs, char **args);int do_stop(int nargs, char **args);int do_swapon_all(int nargs, char **args);int do_trigger(int nargs, char **args);int do_symlink(int nargs, char **args);int do_sysclktz(int nargs, char **args);int do_write(int nargs, char **args);int do_copy(int nargs, char **args);int do_chown(int nargs, char **args);int do_chmod(int nargs, char **args);int do_loglevel(int nargs, char **args);int do_load_persist_props(int nargs, char **args);int do_wait(int nargs, char **args);#define __MAKE_KEYWORD_ENUM__#define KEYWORD(symbol, flags, nargs, func) K_##symbol,enum {    K_UNKNOWN,#endif    KEYWORD(capability,  OPTION,  0, 0)    KEYWORD(chdir,       COMMAND, 1, do_chdir)    KEYWORD(chroot,      COMMAND, 1, do_chroot)    KEYWORD(class,       OPTION,  0, 0)    KEYWORD(class_start, COMMAND, 1, do_class_start)    KEYWORD(class_stop,  COMMAND, 1, do_class_stop)    KEYWORD(class_reset, COMMAND, 1, do_class_reset)    KEYWORD(console,     OPTION,  0, 0)    KEYWORD(critical,    OPTION,  0, 0)    KEYWORD(disabled,    OPTION,  0, 0)    KEYWORD(domainname,  COMMAND, 1, do_domainname)    KEYWORD(exec,        COMMAND, 1, do_exec)    KEYWORD(export,      COMMAND, 2, do_export)    KEYWORD(group,       OPTION,  0, 0)    KEYWORD(hostname,    COMMAND, 1, do_hostname)    KEYWORD(ifup,        COMMAND, 1, do_ifup)    KEYWORD(insmod,      COMMAND, 1, do_insmod)    KEYWORD(import,      SECTION, 1, 0)    KEYWORD(keycodes,    OPTION,  0, 0)    KEYWORD(mkdir,       COMMAND, 1, do_mkdir)    KEYWORD(mount_all,   COMMAND, 1, do_mount_all)    KEYWORD(mount,       COMMAND, 3, do_mount)    KEYWORD(on,          SECTION, 0, 0)    KEYWORD(oneshot,     OPTION,  0, 0)    KEYWORD(onrestart,   OPTION,  0, 0)    KEYWORD(powerctl,    COMMAND, 1, do_powerctl)    KEYWORD(restart,     COMMAND, 1, do_restart)    KEYWORD(restorecon,  COMMAND, 1, do_restorecon)    KEYWORD(restorecon_recursive,  COMMAND, 1, do_restorecon_recursive)    KEYWORD(rm,          COMMAND, 1, do_rm)    KEYWORD(rmdir,       COMMAND, 1, do_rmdir)    KEYWORD(seclabel,    OPTION,  0, 0)    KEYWORD(service,     SECTION, 0, 0)    KEYWORD(setcon,      COMMAND, 1, do_setcon)    KEYWORD(setenforce,  COMMAND, 1, do_setenforce)    KEYWORD(setenv,      OPTION,  2, 0)    KEYWORD(setkey,      COMMAND, 0, do_setkey)    KEYWORD(setprop,     COMMAND, 2, do_setprop)    KEYWORD(setrlimit,   COMMAND, 3, do_setrlimit)    KEYWORD(setsebool,   COMMAND, 2, do_setsebool)    KEYWORD(socket,      OPTION,  0, 0)    KEYWORD(start,       COMMAND, 1, do_start)    KEYWORD(stop,        COMMAND, 1, do_stop)    KEYWORD(swapon_all,  COMMAND, 1, do_swapon_all)    KEYWORD(trigger,     COMMAND, 1, do_trigger)    KEYWORD(symlink,     COMMAND, 1, do_symlink)    KEYWORD(sysclktz,    COMMAND, 1, do_sysclktz)    KEYWORD(user,        OPTION,  0, 0)    KEYWORD(wait,        COMMAND, 1, do_wait)    KEYWORD(write,       COMMAND, 2, do_write)    KEYWORD(copy,        COMMAND, 2, do_copy)    KEYWORD(chown,       COMMAND, 2, do_chown)    KEYWORD(chmod,       COMMAND, 2, do_chmod)    KEYWORD(loglevel,    COMMAND, 1, do_loglevel)    KEYWORD(load_persist_props,    COMMAND, 0, do_load_persist_props)    KEYWORD(ioprio,      OPTION,  0, 0)#ifdef __MAKE_KEYWORD_ENUM__    KEYWORD_COUNT,};#undef __MAKE_KEYWORD_ENUM__#undef KEYWORD#endif

而以上各个命令对应的函数也可以在init目录下面找到，比如mkdir命令对应的函数名称是do_mkdir：

KEYWORD(mkdir,       COMMAND, 1, do_mkdir)

其原型是：

int do_mkdir(int nargs, char **args);

具体实现在./system/core/init/buildins.c中：

int do_mkdir(int nargs, char **args){    mode_t mode = 0755;    int ret;    /* mkdir <path> [mode] [owner] [group] */    if (nargs >= 3) {        mode = strtoul(args[2], 0, 8);    }    ret = make_dir(args[1], mode);    /* chmod in case the directory already exists */    if (ret == -1 && errno == EEXIST) {        ret = _chmod(args[1], mode);    }    if (ret == -1) {        return -errno;    }    if (nargs >= 4) {        uid_t uid = decode_uid(args[3]);        gid_t gid = -1;        if (nargs == 5) {            gid = decode_uid(args[4]);        }        if (_chown(args[1], uid, gid) < 0) {            return -errno;        }        /* chown may have cleared S_ISUID and S_ISGID, chmod again */        if (mode & (S_ISUID | S_ISGID)) {            ret = _chmod(args[1], mode);            if (ret == -1) {                return -errno;            }        }    }    return 0;}