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Kernel command line: earlycon androidboot.selinux=permissive uart_dma keep_dbgclk_on clk_ignore_unused initrd=0xd0000000,38711808 rw crash_page=0x8f040000 initrd=/recoveryrc boot_reason=0x2000 ota_status=0x1001
1、在linux kernel中解析cmdline参数
（以init,rdinit为例）
vim kernel/linux/init/main.c （即kernel_init函数所在的文件）
如代码所示__setup是一个宏，如果cmdline中有这个参数，则会执行对应的后面的函数。
下面这两个函数，会将cmdline中解析到的“init=”、“rdinit=”后面的字串写入到execute_command和ramdisk_execute_command全局变量中.
然后在kernel的代码中，就可以使用这两个变量了.
static int __init init_setup(char *str){unsigned int i;execute_command = str;/** In case LILO is going to boot us with default command line,* it prepends "auto" before the whole cmdline which makes* the shell think it should execute a script with such name.* So we ignore all arguments entered _before_ init=... [MJ]*/for (i = 1; i < MAX_INIT_ARGS; i++)argv_init[i] = NULL;return 1;}__setup("init=", init_setup);static int __init rdinit_setup(char *str){unsigned int i;ramdisk_execute_command = str;/* See "auto" comment in init_setup */for (i = 1; i < MAX_INIT_ARGS; i++)argv_init[i] = NULL;return 1;}__setup("rdinit=", rdinit_setup);
2、在android中解析cmdline参数
(以androidboot.selinux=permissive为例)
如下列代码所示，android的应用程序会读取"/proc/cmdline"中的字符串，然后解析相应的字段,报错到变量中。
vim system/core/init/selinux.cpp
v
oid import_kernel_cmdline(bool in_qemu,const std::function<void(const std::string&, const std::string&, bool)>& fn) {std::string cmdline;android::base::ReadFileToString("/proc/cmdline", &cmdline);for (const auto& entry : android::base::Split(android::base::Trim(cmdline), " ")) {std::vector<std::string> pieces = android::base::Split(entry, "=");if (pieces.size() == 2) {fn(pieces[0], pieces[1], in_qemu);}}}
vim system/core/init/util.cpp
EnforcingStatus StatusFromCmdline() {EnforcingStatus status = SELINUX_ENFORCING;import_kernel_cmdline(false,[&](const std::string& key, const std::string& value, bool in_qemu) {if (key == "androidboot.selinux" && value == "permissive") {status = SELINUX_PERMISSIVE;}});return status;}
