Android 的init过程详解
文章出处：http://blog.csdn.net/shift_wwx
init进程是用户空间执行的第一个进程，直接进入code：/system/core/init/init.c
int main(int argc, char **argv)
{
int fd_count = 0;
struct pollfd ufds[4];
char *tmpdev;
char* debuggable;
char tmp[32];
int property_set_fd_init = 0;
int signal_fd_init = 0;
int keychord_fd_init = 0;
bool is_charger = false;
if (!strcmp(basename(argv[0]), "ueventd"))
return ueventd_main(argc, argv);
if (!strcmp(basename(argv[0]), "watchdogd"))
return watchdogd_main(argc, argv);
/* clear the umask */
umask(0);
/* Get the basic filesystem setup we need put
* together in the initramdisk on / and then we'll
* let the rc file figure out the rest.
*/
mkdir("/dev", 0755);
mkdir("/proc", 0755);
mkdir("/sys", 0755);
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
mount("proc", "/proc", "proc", 0, NULL);
mount("sysfs", "/sys", "sysfs", 0, NULL);
/* indicate that booting is in progress to background fw loaders, etc */
close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000));
/* We must have some place other than / to create the
* device nodes for kmsg and null, otherwise we won't
* be able to remount / read-only later on.
* Now that tmpfs is mounted on /dev, we can actually
* talk to the outside world.
*/
open_devnull_stdio();
klog_init();
property_init();
get_hardware_name(hardware, &revision);
process_kernel_cmdline();
union selinux_callback cb;
cb.func_log = klog_write;
selinux_set_callback(SELINUX_CB_LOG, cb);
cb.func_audit = audit_callback;
selinux_set_callback(SELINUX_CB_AUDIT, cb);
selinux_initialize();
/* These directories were necessarily created before initial policy load
* and therefore need their security context restored to the proper value.
* This must happen before /dev is populated by ueventd.
*/
restorecon("/dev");
restorecon("/dev/socket");
restorecon("/dev/__properties__");
restorecon_recursive("/sys");
is_charger = !strcmp(bootmode, "charger");
INFO("property init\n");
if (!is_charger)
property_load_boot_defaults();
if (!strcmp(bootmode,"factory"))
init_parse_config_file("/init.factorytest.rc");
else if (!strcmp(bootmode,"factory2"))
init_parse_config_file("/init.factorytest2.rc");
else
init_parse_config_file("/init.rc");
action_for_each_trigger("early-init", action_add_queue_tail);
queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");
queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
queue_builtin_action(keychord_init_action, "keychord_init");
queue_builtin_action(console_init_action, "console_init");
/* execute all the boot actions to get us started */
action_for_each_trigger("init", action_add_queue_tail);
aml_firstbootinit();
/* skip mounting filesystems in charger mode */
if (!is_charger) {
action_for_each_trigger("early-fs", action_add_queue_tail);
action_for_each_trigger("fs", action_add_queue_tail);
action_for_each_trigger("post-fs", action_add_queue_tail);
action_for_each_trigger("post-fs-data", action_add_queue_tail);
}
/* Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
* wasn't ready immediately after wait_for_coldboot_done
*/
queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
queue_builtin_action(property_service_init_action, "property_service_init");
queue_builtin_action(signal_init_action, "signal_init");
queue_builtin_action(check_startup_action, "check_startup");
/* run all property triggers based on current state of the properties */
queue_builtin_action(queue_property_triggers_action, "queue_property_triggers");
if (is_charger) {
action_for_each_trigger("charger", action_add_queue_tail);
} else {
action_for_each_trigger("early-boot", action_add_queue_tail);
queue_builtin_action(ubootenv_init_action, "ubootenv_init");
queue_builtin_action(set_firstboot_complete_flag, "firstboot_complete");
action_for_each_trigger("boot", action_add_queue_tail);
}
#if BOOTCHART
queue_builtin_action(bootchart_init_action, "bootchart_init");
#endif
for(;;) {
int nr, i, timeout = -1;
execute_one_command();
restart_processes();
if (!property_set_fd_init && get_property_set_fd() > 0) {
ufds[fd_count].fd = get_property_set_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
property_set_fd_init = 1;
}
if (!signal_fd_init && get_signal_fd() > 0) {
ufds[fd_count].fd = get_signal_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
signal_fd_init = 1;
}
if (!keychord_fd_init && get_keychord_fd() > 0) {
ufds[fd_count].fd = get_keychord_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
keychord_fd_init = 1;
}
if (process_needs_restart) {
timeout = (process_needs_restart - gettime()) * 1000;
if (timeout < 0)
timeout = 0;
}
if (!action_queue_empty() || cur_action)
timeout = 0;
#if BOOTCHART
if (bootchart_count > 0) {
if (timeout < 0 || timeout > BOOTCHART_POLLING_MS)
timeout = BOOTCHART_POLLING_MS;
if (bootchart_step() < 0 || --bootchart_count == 0) {
bootchart_finish();
bootchart_count = 0;
}
}
#endif
nr = poll(ufds, fd_count, timeout);
if (nr <= 0)
continue;
for (i = 0; i < fd_count; i++) {
if (ufds[i].revents == POLLIN) {
if (ufds[i].fd == get_property_set_fd())
handle_property_set_fd();
else if (ufds[i].fd == get_keychord_fd())
handle_keychord();
else if (ufds[i].fd == get_signal_fd())
handle_signal();
}
}
}
return 0;
}
1、创建文件系统目录并挂载相关的文件系统
mkdir("/dev", 0755);
mkdir("/proc", 0755);
mkdir("/sys", 0755);
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
mount("proc", "/proc", "proc", 0, NULL);
mount("sysfs", "/sys", "sysfs", 0, NULL); 目前Linux有很多通讯机制可以在用户空间和内核空间之间交互，例如设备驱动文件（位于/dev目录中）、内存文件（/proc、/sys目录等）。了解Linux的同学都应该知道Linux的重要特征之一就是一切都是以文件的形式存在的，例如，一个设备通常与一个或多个设备文件对应。这些与内核空间交互的文件都在用户空间，所以在Linux内核装载完，需要首先建立这些文件所在的目录。
1.1 在init初始化过程中，Android分别挂载了tmpfs，devpts，proc，sysfs 4类文件系统
1.1.1 tmpfs文件系统
tmpfs是一种虚拟内存文件系统，因此它会将所有的文件存储在虚拟内存中，并且tmpfs下的所有内容均为临时性的内容，如果你将tmpfs文件系统卸载后，那么其下的所有的内容将不复存在。
tmpfs有些像虚拟磁盘（ramdisk），但不是一回事。说其像虚拟磁盘，是因为它可以使用你的RAM，但它也可以使用你的交换分区。传统的虚拟磁盘是一个块设备，而且需要一个mkfs之类的命令格式化它才能使用。tmpfs是一个独立的文件系统，不是块设备，只要挂接，立即就可以使用。
tmpfs的大下是不确定的，它最初只有很小的空间，但随着文件的复制和创建，它的大小就会不断变化，换句话说，它会根据你的实际需要而改变大小；tmpfs的速度非常惊人，毕竟它是驻留在RAM中的，即使用了交换分区，性能仍然非常卓越；由于tmpfs是驻留在RAM的，因此它的内容是不持久的，断电后，tmpfs的内容就消失了，这也是被称作tmpfs的根本原因。
1.1.2 devpts文件系统
devpts文件系统为伪终端提供了一个标准接口，它的标准挂接点是/dev/pts。只要pty的主复合设备/dev/ptmx被打开，就会在/dev/pts下动态的创建一个新的pty设备文件。
1.1.3 proc文件系统
proc文件系统是一个非常重要的虚拟文件系统，它可以看作是内核内部数据结构的接口，通过它我们可以获得系统的信息，同时也能够在运行时修改特定的内核参数。
在proc文件系统中，你可以修改内核的参数，是不是很强大？怎么修改呢?你只需要echo一个新的值到对应的文件中即可，但是如果在修改过程中发生错误的话，那么你将别无选择，只能重启设备。
1.1.4 sysfs文件系统
与proc文件系统类似，sysfs文件系统也是一个不占有任何磁盘空间的虚拟文件系统。它通常被挂接在/sys目录下。sysfs文件系统是Linux2.6内核引入的，它把连接在系统上的设备和总线组织成为一个分级的文件，使得它们可以在用户空间存取。
2、查看.booting是否有读写权限
/* indicate that booting is in progress to background fw loaders, etc */
close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000));
3、屏蔽标准的输入输出，即标准的输入输出定向到NULL设备。
open_devnull_stdio();
void open_devnull_stdio(void)
{
int fd;
static const char *name = "/dev/__null__";
//创建一个字符专用文件
if (mknod(name, S_IFCHR | 0600, (1 << 8) | 3) == 0) {
fd = open(name, O_RDWR);
unlink(name);
//将与进程相关的标准输入(0)、标准输出(1)、标准出错(2)都定向到null
if (fd >= 0) {
dup2(fd, 0);
dup2(fd, 1);
dup2(fd, 2);
if (fd > 2) {
close(fd);
}
return;
}
}
exit(1);
} 这里解释一下
dup2(fd, 0);
dup2(fd, 1);
dup2(fd, 2);
过程：
首先说明以下dup2的作用，这个函数主要是复制一个函数的描述符，一般用于重定向进程的stdin，stdout，stderr。它的原型如下：
int dup2(int oldfd, int newfd);
dup2(fd, 0);
dup2(fd, 1);
dup2(fd, 2);
这三次调用一次将依次代表stdin，stdout，stderr的描述符0，1，2，重定向到dev/null,通过这种方式达到屏蔽标准输入输出的作用。
4、初始化内核log系统
klog_init();
void klog_init(void)
{
static const char *name = "/dev/__kmsg__";
if (klog_fd >= 0) return; /* Already initialized */
if (mknod(name, S_IFCHR | 0600, (1 << 8) | 11) == 0) {
klog_fd = open(name, O_WRONLY);
if (klog_fd < 0)
return;
fcntl(klog_fd, F_SETFD, FD_CLOEXEC);
unlink(name);
}
}
有上述实现看出内核的log输出是通过文件描述符log_fd写入的，那到底写入到什么设备呢？/dev/kmsg，这个设备则会把它收到的任何写入都作为printk的输出。printk函数是内核中运行的向控制台输出显示的函数。
5、初始化属性空间
property_init();
为属性分配一些存储空间。
static int init_property_area(void)
{
if (property_area_inited)
return -1;
if(__system_property_area_init())
return -1;
if(init_workspace(&pa_workspace, 0))
return -1;
fcntl(pa_workspace.fd, F_SETFD, FD_CLOEXEC);
property_area_inited = 1;
return 0;
}第一个变量，就是为了防止重新init；
__system_property_area_init()函数来看一下source code：
@/bionic/libc/bionic/system_properties.c
int __system_property_area_init()
{
return map_prop_area_rw();
}
static int map_prop_area_rw()
{
prop_area *pa;
int fd;
int ret;
/* dev is a tmpfs that we can use to carve a shared workspace
* out of, so let's do that...
*/
fd = open(property_filename, O_RDWR | O_CREAT | O_NOFOLLOW | O_CLOEXEC |
O_EXCL, 0444);//打开文件property_filename，头文件中有定义：/dev/__properties__
if (fd < 0) {
if (errno == EACCES) {
/* for consistency with the case where the process has already
* mapped the page in and segfaults when trying to write to it
*/
abort();
}
return -1;
}
ret = fcntl(fd, F_SETFD, FD_CLOEXEC);//这里设置为FD_CLOEXEC表示当程序执行exec函数时本fd将被系统自动关闭,表示不传递给exec创建的新进程
if (ret < 0)
goto out;
if (ftruncate(fd, PA_SIZE) < 0)//更改fd指向文件的大小为PA_SIZE(128 * 1024)大小
goto out;
pa_size = PA_SIZE;
pa_data_size = pa_size - sizeof(prop_area);
compat_mode = false;
pa = mmap(NULL, pa_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);//用的是共享内存
if(pa == MAP_FAILED)
goto out;
memset(pa, 0, pa_size);
pa->magic = PROP_AREA_MAGIC;
pa->version = PROP_AREA_VERSION;
/* reserve root node */
pa->bytes_used = sizeof(prop_bt);
/* plug into the lib property services */
__system_property_area__ = pa;
close(fd);
return 0;
out:
close(fd);
return -1;
}
6、获取hardware和revision值
get_hardware_name(hardware, &revision);
void get_hardware_name(char *hardware, unsigned int *revision)
{
char data[1024];
int fd, n;
char *x, *hw, *rev;
/* Hardware string was provided on kernel command line */
if (hardware[0])
return;
fd = open("/proc/cpuinfo", O_RDONLY);
if (fd < 0) return;
n = read(fd, data, 1023);
close(fd);
if (n < 0) return;
data[n] = 0;
hw = strstr(data, "\nHardware");
rev = strstr(data, "\nRevision");
if (hw) {
x = strstr(hw, ": ");
if (x) {
x += 2;
n = 0;
while (*x && *x != '\n' && !isspace(*x)) {
hardware[n++] = tolower(*x);
x++;
if (n == 31) break;
}
hardware[n] = 0;
}
}
if (rev) {
x = strstr(rev, ": ");
if (x) {
*revision = strtoul(x + 2, 0, 16);
}
}
}从/proc/cpuinfo中读取1023个字节存入data中，并查找第一次出现Hardware和Revision的地方。然后进行一系列的解析，最终获得hardware和revision。
这个hardware和revision是干嘛的呢？
code中给出了答案：
/* if this was given on kernel command line, override what we read
* before (e.g. from /proc/cpuinfo), if anything */
ret = property_get("ro.boot.hardware", tmp);
if (ret)
strlcpy(hardware, tmp, sizeof(hardware));
property_set("ro.hardware", hardware);
snprintf(tmp, PROP_VALUE_MAX, "%d", revision);
property_set("ro.revision", tmp);如果ro.boot.hardware有值，hardware会被重置，如果没有，从之前获取的hardware值会将ro.hardware置上。
ro.revision则是通过之前获取的revision值置上的。
ro.hardware这个属性，会在后面解析init.rc的时候用到：
import /init.${ro.hardware}.rc7、process_kernel_cmdline();
static void process_kernel_cmdline(void)
{
/* don't expose the raw commandline to nonpriv processes */
chmod("/proc/cmdline", 0440);
/* first pass does the common stuff, and finds if we are in qemu.
* second pass is only necessary for qemu to export all kernel params
* as props.
*/
import_kernel_cmdline(0, import_kernel_nv);
if (qemu[0])
import_kernel_cmdline(1, import_kernel_nv);
/* now propogate the info given on command line to internal variables
* used by init as well as the current required properties
*/
export_kernel_boot_props();
}7.1 import_kernel_cmdline主要是导入一些内核变量。
cat /proc/cmdline：
init=/init console=ttyS0,115200n8 mem=1024m logo=osd0,loaded,panel mac=00:15:18:01:81:31具体怎么实现的主要是函数import_kernel_nv：
static void import_kernel_nv(char *name, int for_emulator)
{
char *value = strchr(name, '=');
int name_len = strlen(name);
if (value == 0) return;
*value++ = 0;
if (name_len == 0) return;
if (for_emulator) {
/* in the emulator, export any kernel option with the
* ro.kernel. prefix */
char buff[PROP_NAME_MAX];
int len = snprintf( buff, sizeof(buff), "ro.kernel.%s", name );
if (len < (int)sizeof(buff))
property_set( buff, value );
return;
}
if (!strcmp(name,"qemu")) {
strlcpy(qemu, value, sizeof(qemu));
} else if (!strncmp(name, "androidboot.", 12) && name_len > 12) {
const char *boot_prop_name = name + 12;
char prop[PROP_NAME_MAX];
int cnt;
if (!strcmp(name,"androidboot.resolution")) {
strlcpy(resolution, value, sizeof(resolution));
}
if (!strcmp(name,"androidboot.realoutput")) {
strlcpy(realoutput, value, sizeof(realoutput));
ERROR("androidboot.realoutput:%s\n",realoutput);
}
cnt = snprintf(prop, sizeof(prop), "ro.boot.%s", boot_prop_name);
if (cnt < PROP_NAME_MAX)
property_set(prop, value);
} else if (!strcmp(name,"hdmimode")) {
strlcpy(hdmimode, value, sizeof(hdmimode));
} else if (!strcmp(name,"cvbsmode")) {
strlcpy(cvbsmode, value, sizeof(cvbsmode));
}
}从code中可以看出来，主要找一个resolution、hdmimode、cvbsmode等。
其中ro.boot.%s需要注意了，这里boot相关的prop就是之前读到的/prop/cmdline中console、hardware、mac、mem等。后面就会看到了
7.2 export_kernel_boot_props();
static void export_kernel_boot_props(void)
{
char tmp[PROP_VALUE_MAX] = {0};
int ret;
unsigned i;
#ifdef CUSTOMER_SERIALNO_MAC
struct {
const char *src_prop;
const char *dest_prop;
const char *def_val;
} prop_map[] = {
{ "ro.boot.serialno", "ro.serialno", "00AA000102090300015F881036202785", },
{ "ro.boot.mode", "ro.bootmode", "unknown", },
{ "ro.boot.baseband", "ro.baseband", "unknown", },
{ "ro.boot.bootloader", "ro.bootloader", "unknown", },
{ "ro.boot.firstboot", "ro.firstboot", "0"},
};
#else
struct {
const char *src_prop;
const char *dest_prop;
const char *def_val;
} prop_map[] = {
{ "ro.boot.serialno", "ro.serialno", "12345678900", },
{ "ro.boot.mode", "ro.bootmode", "unknown", },
{ "ro.boot.baseband", "ro.baseband", "unknown", },
{ "ro.boot.bootloader", "ro.bootloader", "unknown", },
{ "ro.boot.firstboot", "ro.firstboot", "0"},
};
#endif
for (i = 0; i < ARRAY_SIZE(prop_map); i++) {
ret = property_get(prop_map[i].src_prop, tmp);
if (ret > 0)
property_set(prop_map[i].dest_prop, tmp);
else
property_set(prop_map[i].dest_prop, prop_map[i].def_val);
}
ret = property_get("ro.boot.console", tmp);
if (ret)
strlcpy(console, tmp, sizeof(console));
/* save a copy for init's usage during boot */
property_get("ro.bootmode", tmp);
strlcpy(bootmode, tmp, sizeof(bootmode));
/* if this was given on kernel command line, override what we read
* before (e.g. from /proc/cpuinfo), if anything */
ret = property_get("ro.boot.hardware", tmp);
if (ret)
strlcpy(hardware, tmp, sizeof(hardware));
property_set("ro.hardware", hardware);
snprintf(tmp, PROP_VALUE_MAX, "%d", revision);
property_set("ro.revision", tmp);
/* TODO: these are obsolete. We should delete them */
if (!strcmp(bootmode,"factory"))
property_set("ro.factorytest", "1");
else if (!strcmp(bootmode,"factory2"))
property_set("ro.factorytest", "2");
else
property_set("ro.factorytest", "0");
#ifdef CUSTOMER_SERIALNO_MAC
property_set("ro.mac", "00:22:7E:0B:53:26");
#endif
}可以看出这里主要ro.boot.console等属性就是之前通过import_kernel_nv解析出来的prop，而之前提到过的ro.boot.hardware也是需要import_kernel_nv解析，如果没有设置的话hardware的值就是通过/proc/cpuinfo来的。
8、解析init.rc
if (!strcmp(bootmode,"factory"))
init_parse_config_file("/init.factorytest.rc");
else if (!strcmp(bootmode,"factory2"))
init_parse_config_file("/init.factorytest2.rc");
else
init_parse_config_file("/init.rc");根据启动模式，加载init.rc
action_for_each_trigger("early-init", action_add_queue_tail);
/* execute all the boot actions to get us started */
action_for_each_trigger("init", action_add_queue_tail);
aml_firstbootinit();
/* skip mounting filesystems in charger mode */
if (!is_charger) {
action_for_each_trigger("early-fs", action_add_queue_tail);
action_for_each_trigger("fs", action_add_queue_tail);
action_for_each_trigger("post-fs", action_add_queue_tail);
action_for_each_trigger("post-fs-data", action_add_queue_tail);
}
if (is_charger) {
action_for_each_trigger("charger", action_add_queue_tail);
} else {
action_for_each_trigger("early-boot", action_add_queue_tail);
queue_builtin_action(ubootenv_init_action, "ubootenv_init");
queue_builtin_action(set_firstboot_complete_flag, "firstboot_complete");
action_for_each_trigger("boot", action_add_queue_tail);
}根据流程，确定了trigger的顺序。从on early-init 、on init、on early-fs、on fs。。。，将这些action去不放到action链表中。
至于init.rc的详细解释，可以看一下《 Android init.rc详解》。
9、action queue
/* Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
* wasn't ready immediately after wait_for_coldboot_done
*/
queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
queue_builtin_action(property_service_init_action, "property_service_init");
queue_builtin_action(signal_init_action, "signal_init");
queue_builtin_action(check_startup_action, "check_startup");
/* run all property triggers based on current state of the properties */
queue_builtin_action(queue_property_triggers_action, "queue_property_triggers");
还有一些配置也会存储在action链表中，参数前面是command的函数，后面的action name。
其中解释一下：
queue_builtin_action(property_service_init_action, "property_service_init");
static int property_service_init_action(int nargs, char **args)
{
/* read any property files on system or data and
* fire up the property service. This must happen
* after the ro.foo properties are set above so
* that /data/local.prop cannot interfere with them.
*/
start_property_service();
return 0;
}
void start_property_service(void)
{
int fd;
load_properties_from_file(PROP_PATH_SYSTEM_BUILD);
load_properties_from_file(PROP_PATH_SYSTEM_DEFAULT);
load_override_properties();
/* Read persistent properties after all default values have been loaded. */
load_persistent_properties();
fd = create_socket(PROP_SERVICE_NAME, SOCK_STREAM, 0666, 0, 0);
if(fd < 0) return;
fcntl(fd, F_SETFD, FD_CLOEXEC);
fcntl(fd, F_SETFL, O_NONBLOCK);
listen(fd, 8);
property_set_fd = fd;
}
就是加载一些prop，其中的过程还是比较复杂的。可以看一下我之前小结的一篇博文《Android系统中prop的使用》
其中的宏是定义在bionic/libc/include/sys/_system_properties.h
#define PROP_PATH_RAMDISK_DEFAULT "/default.prop" #define PROP_PATH_SYSTEM_BUILD "/system/build.prop" #define PROP_PATH_SYSTEM_DEFAULT "/system/default.prop" #define PROP_PATH_LOCAL_OVERRIDE "/data/local.prop" #define PROP_PATH_FACTORY "/factory/factory.prop"还有个persistent
#define PERSISTENT_PROPERTY_DIR "/data/property"10、死循环
for(;;) {
int nr, i, timeout = -1;
execute_one_command();
restart_processes();
if (!property_set_fd_init && get_property_set_fd() > 0) {
ufds[fd_count].fd = get_property_set_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
property_set_fd_init = 1;
}
if (!signal_fd_init && get_signal_fd() > 0) {
ufds[fd_count].fd = get_signal_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
signal_fd_init = 1;
}
if (!keychord_fd_init && get_keychord_fd() > 0) {
ufds[fd_count].fd = get_keychord_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
keychord_fd_init = 1;
}
if (process_needs_restart) {
timeout = (process_needs_restart - gettime()) * 1000;
if (timeout < 0)
timeout = 0;
}
if (!action_queue_empty() || cur_action)
timeout = 0;
#if BOOTCHART
if (bootchart_count > 0) {
if (timeout < 0 || timeout > BOOTCHART_POLLING_MS)
timeout = BOOTCHART_POLLING_MS;
if (bootchart_step() < 0 || --bootchart_count == 0) {
bootchart_finish();
bootchart_count = 0;
}
}
#endif
nr = poll(ufds, fd_count, timeout);
if (nr <= 0)
continue;
for (i = 0; i < fd_count; i++) {
if (ufds[i].revents == POLLIN) {
if (ufds[i].fd == get_property_set_fd())
handle_property_set_fd();
else if (ufds[i].fd == get_keychord_fd())
handle_keychord();
else if (ufds[i].fd == get_signal_fd())
handle_signal();
}
}
}10.1 依次执行action序列
execute_one_command();
void execute_one_command(void)
{
int ret;
if (!cur_action || !cur_command || is_last_command(cur_action, cur_command)) {
cur_action = action_remove_queue_head();
cur_command = NULL;
if (!cur_action)
return;
INFO("processing action %p (%s)\n", cur_action, cur_action->name);
cur_command = get_first_command(cur_action);
} else {
cur_command = get_next_command(cur_action, cur_command);
}
if (!cur_command)
return;
ret = cur_command->func(cur_command->nargs, cur_command->args);
INFO("command '%s' r=%d\n", cur_command->args[0], ret);
}依次执行，一直到最后一个action command。
10.2 重启所有需要重启的services
restart_processes();
static void restart_processes()
{
process_needs_restart = 0;
service_for_each_flags(SVC_RESTARTING,
restart_service_if_needed);
}也就是说对SVC_RESTARTING相关的service做restart_service_if_needed操作。
10.3 对3个文件描述符进行轮询
分别是property_set_fd、keychord_fd、signal_fd。
for (i = 0; i < fd_count; i++) {
if (ufds[i].revents == POLLIN) {
if (ufds[i].fd == get_property_set_fd())
handle_property_set_fd();//处理prop
else if (ufds[i].fd == get_keychord_fd())
handle_keychord();
else if (ufds[i].fd == get_signal_fd())
handle_signal();//处理SIGCHLD信号
}
}
这三个fd可以说android系统启动后最关键的监听器了，需要好好分析一下。
1）property_set_fd
在Android系统中prop详解中讲了prop set的过程，会创建一个property_service的socket，并对其listen。
......
具体的稍后补充说明。
参考文献：
http://www.cnblogs.com/nokiaguy/archive/2013/04/14/3020774.html
http://blog.csdn.net/windskier/article/details/6416547