Linux启动参数及实现.doc

Linux启动参数及实现 _setup与early_param #define _setup_param(str, unique_id, fn, early) / static char _setup_str_#unique_id _initdata = str; / static struct obs_kernel_param _setup_#unique_id / _attribute_used_ / _attribute_(_section_(.init.setup) / _attribute_(aligned(sizeof(long) / = _setup_str_#unique_id, fn, early #define _setup(str, fn) / _setup_param(str, fn, fn, 0) #define early_param(str, fn) / _setup_param(str, fn, fn, 1)_setup与early_param不同的是，early_param 宏注册的内核选项必须要在其他内核选项之前被处理。在函数start_kernel中，parse_early_param处理early_param定义的参数，parse_args处理_setup定义的参数。parse_early_param();parse_args(Booting kernel, static_command_line, _start_param, _stop_param - _start_param, &unknown_bootoption); 1,所有的系统启动参数都是由形如 static int _init foo(char *str);的函数来支持的注:#define _init _attribute_ (_section_ (.init.text)申明所有的启动参数支持函数都放入.init.text段2.1,用_setup宏来导出参数的支持函数_setup(foo= , foo);展开后就是如下的形式static char _setup_str_foo _initdata = foo=; static struct obs_kernel_param _setup_foo _attribute_used_ _attribute_(_section_(.init.setup) _attribute_(aligned(sizeof(long) = _setup_str_foo, foo, 0 ;/foo=,foo,0也就是说,启动参数(函数指针)被封装到obs_kernel_param结构中,所有的内核启动参数形成内核映像.init.setup段中的一个obs_kernel_param数组2.2用early_param宏来申明需要早期处理的启动参数,例如在arch/i386/kernel/setup.c就有如下的申明:early_param(mem, parse_mem);展开后和_setup是一样的只是early参数不一样,因此会在do_early_param中被处理3,内核对启动参数的解析:下面函数历遍obs_kernel_param数组,调用支持函数static int _init do_early_param(char *param, char *val) struct obs_kernel_param *p; for (p = _setup_start; p early & strcmp(param, p-str) = 0) if (p-setup_func(val) != 0) printk(KERN_WARNING Malformed early option %s/n, param); /* We accept everything at this stage. */ return 0;这个函数在parse_early_param中被调用,而parse_early_param在start_kernel中被调用,parse_early_param之后的parse_args会调用下面函数static int _init obsolete_checksetup(char *line) struct obs_kernel_param *p; int had_early_param = 0; p = _setup_start; do int n = strlen(p-str); if (!strncmp(line, p-str, n) if (p-early) /* Already done in parse_early_param? * (Needs exact match on param part). * Keep iterating, as we can have early * params and _setups of same names 8( */ if (linen = /0 | linen = =) had_early_param = 1; else if (!p-setup_func) printk(KERN_WARNING Parameter %s is obsolete, ignored/n, p-str); return 1; else if (p-setup_func(line + n)/调用支持函数 return 1; p+; while (p _setup_end); return had_early_param;init/main.c中启动参数申明列表:_setup(nosmp, nosmp);_setup(maxcpus=, maxcpus);_setup(reset_devices, set_reset_devices);_setup(debug, debug_kernel);_setup(quiet, quiet_kernel