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上一节我们分析的earlay的printk知识，本节主要分析一下在内核启动后的printk的知识。
主要是通过下面函数实现的
after_dashes = parse_args("Booting kernel",
static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, NULL, &unknown_bootoption);
这里又有一个段属性，_param，通过下面方式定义
/* This is the fundamental function for registering boot/module
parameters. */
#define __module_param_call(prefix, name, ops, arg, perm, level, flags) \
/* Default value instead of permissions? */ \
static const char __param_str_##name[] = prefix #name; \
static struct kernel_param __moduleparam_const __param_##name \
__used \
__attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
= { __param_str_##name, THIS_MODULE, ops, \
VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg } }
/* Obsolete - use module_param_cb() */
#define module_param_call(name, _set, _get, arg, perm) \
static const struct kernel_param_ops __param_ops_##name = \
{ .flags = 0, .set = _set, .get = _get }; \
__module_param_call(MODULE_PARAM_PREFIX, \
name, &__param_ops_##name, arg, perm, -1, 0)
主要由下面这两个结构体组成。
struct kernel_param {
const char *name;
struct module *mod;
const struct kernel_param_ops *ops;
const u16 perm;
s8 level;
u8 flags;
union {
void *arg;
const struct kparam_string *str;
const struct kparam_array *arr;
};
};
struct kernel_param_ops {
/* How the ops should behave */
unsigned int flags;
/* Returns 0, or -errno. arg is in kp->arg. */
int (*set)(const char *val, const struct kernel_param *kp);
/* Returns length written or -errno. Buffer is 4k (ie. be short!) */
int (*get)(char *buffer, const struct kernel_param *kp);
/* Optional function to free kp->arg when module unloaded. */
void (*free)(void *arg);
};
可以看到，这个结构体中，.name = __param_str_##name
/* This is the fundamental function for registering boot/module
parameters. */
#define __module_param_call(prefix, name, ops, arg, perm, level, flags) \
/* Default value instead of permissions? */ \
static const char __param_str_##name[] = prefix #name; \
static struct kernel_param __moduleparam_const __param_##name \
__used \
__attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
= { __param_str_##name, THIS_MODULE, ops, \
VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg } }
/* Obsolete - use module_param_cb() */
#define module_param_call(name, _set, _get, arg, perm) \
static const struct kernel_param_ops __param_ops_##name = \
{ .flags = 0, .set = _set, .get = _get }; \
__module_param_call(MODULE_PARAM_PREFIX, \
name, &__param_ops_##name, arg, perm, -1, 0)
我们已经知道了这里是依次拿出cmdline中的每个命令和params中的进行比较，
/* Args looks like "foo=bar,bar2 baz=fuz wiz". */
char *parse_args(const char *doing,
char *args,
const struct kernel_param *params,
unsigned num,
s16 min_level,
s16 max_level,
void *arg,
int (*unknown)(char *param, char *val,
const char *doing, void *arg))
{
char *param, *val, *err = NULL;
/* Chew leading spaces */
args = skip_spaces(args);
if (*args)
pr_debug("doing %s, parsing ARGS: '%s'\n", doing, args);
while (*args) {
int ret;
int irq_was_disabled;
args = next_arg(args, ¶m, &val);
/* Stop at -- */
if (!val && strcmp(param, "--") == 0)
return err ?: args;
irq_was_disabled = irqs_disabled();
ret = parse_one(param, val, doing, params, num,
min_level, max_level, arg, unknown);
if (irq_was_disabled && !irqs_disabled())
pr_warn("%s: option '%s' enabled irq's!\n",
doing, param);
switch (ret) {
case 0:
continue;
case -ENOENT:
pr_err("%s: Unknown parameter `%s'\n", doing, param);
break;
case -ENOSPC:
pr_err("%s: `%s' too large for parameter `%s'\n",
doing, val ?: "", param);
break;
default:
pr_err("%s: `%s' invalid for parameter `%s'\n",
doing, val ?: "", param);
break;
}
err = ERR_PTR(ret);
}
return err;
}
要是相等会执行，会对参数检测后，执行ops里面的set函数。然后退出。
当然这个函数还有另一个作用就是不匹配不成功的情况下，执行handle_unknown函数。
static int parse_one(char *param,
char *val,
const char *doing,
const struct kernel_param *params,
unsigned num_params,
s16 min_level,
s16 max_level,
void *arg,
int (*handle_unknown)(char *param, char *val,
const char *doing, void *arg))
{
unsigned int i;
int err;
/* Find parameter */
for (i = 0; i < num_params; i++) {
if (parameq(param, params[i].name)) {
if (params[i].level < min_level
|| params[i].level > max_level)
return 0;
/* No one handled NULL, so do it here. */
if (!val &&
!(params[i].ops->flags & KERNEL_PARAM_OPS_FL_NOARG))
return -EINVAL;
pr_debug("handling %s with %p\n", param,
params[i].ops->set);
kernel_param_lock(params[i].mod);
param_check_unsafe(¶ms[i]);
err = params[i].ops->set(val, ¶ms[i]);
kernel_param_unlock(params[i].mod);
return err;
}
}
if (handle_unknown) {
pr_debug("doing %s: %s='%s'\n", doing, param, val);
return handle_unknown(param, val, doing, arg);
}
pr_debug("Unknown argument '%s'\n", param);
return -ENOENT;
}当然这里的handle_unknown函数就是我们本次的重点了。
也就是cmdline中的每个命令，如果和__start___param段属性中的所有都没匹配成功，就会执行一次handle_unknown函数，在我们这里也就是下面的这个unknown_bootoption函数。
/*
* Unknown boot options get handed to init, unless they look like
* unused parameters (modprobe will find them in /proc/cmdline).
*/
static int __init unknown_bootoption(char *param, char *val,
const char *unused, void *arg)
{
repair_env_string(param, val, unused, NULL);
/* Handle obsolete-style parameters */
if (obsolete_checksetup(param))
return 0;
/* Unused module parameter. */
if (strchr(param, '.') && (!val || strchr(param, '.') < val))
return 0;
if (panic_later)
return 0;
if (val) {
/* Environment option */
unsigned int i;
for (i = 0; envp_init[i]; i++) {
if (i == MAX_INIT_ENVS) {
panic_later = "env";
panic_param = param;
}
if (!strncmp(param, envp_init[i], val - param))
break;
}
envp_init[i] = param;
} else {
/* Command line option */
unsigned int i;
for (i = 0; argv_init[i]; i++) {
if (i == MAX_INIT_ARGS) {
panic_later = "init";
panic_param = param;
}
}
argv_init[i] = param;
}
return 0;
}
这里的传参分为三种，一种是过时的参数解析，一种是val表示传的是环境变量，第二种是没有val即为NULL时，是传的命令行参数。
我们这里是设备树传过来的chosen里面的命令行，一些命令行是过时的，一些则不是
static bool __init obsolete_checksetup(char *line)
{
const struct obs_kernel_param *p;
bool had_early_param = false;
p = __setup_start;
do {
int n = strlen(p->str);
if (parameqn(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 (line[n] == '\0' || line[n] == '=')
had_early_param = true;
} else if (!p->setup_func) {
pr_warn("Parameter %s is obsolete, ignored\n",
p->str);
return true;
} else if (p->setup_func(line + n))
return true;
}
p++;
} while (p < __setup_end);
return had_early_param;
}
这个函数上一节分析过，在.init.setup段属性中查找是否存这个cmdline传过来的命令。
分为earlay和非earlay，因为earlay阶段已经过去，这里的都是普通的。
看一下我们的命令行参数有
root=/dev/nfs nfsroot=192.168.0.101:/home/run/work/rootfs/rootfs_3.16.57
ip=192.168.0.20:192.168.0.101:192.168.0.1:255.255.255.0::eth0:off init=/linuxrc
console=ttySAC2,115200 earlyprintk
- root
- nfsroot
- init
- console
static int __init root_dev_setup(char *line)
{
strlcpy(saved_root_name, line, sizeof(saved_root_name));
return 1;
}
__setup("root=", root_dev_setup);
/*
* Parse NFS server and directory information passed on the kernel
* command line.
*
* nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
*
* If there is a "%s" token in the <root-dir> string, it is replaced
* by the ASCII-representation of the client's IP address.
*/
static int __init nfs_root_setup(char *line)
{
ROOT_DEV = Root_NFS;
if (line[0] == '/' || line[0] == ',' || (line[0] >= '0' && line[0] <= '9')) {
strlcpy(nfs_root_parms, line, sizeof(nfs_root_parms));
} else {
size_t n = strlen(line) + sizeof(NFS_ROOT) - 1;
if (n >= sizeof(nfs_root_parms))
line[sizeof(nfs_root_parms) - sizeof(NFS_ROOT) - 2] = '\0';
sprintf(nfs_root_parms, NFS_ROOT, line);
}
/*
* Extract the IP address of the NFS server containing our
* root file system, if one was specified.
*
* Note: root_nfs_parse_addr() removes the server-ip from
* nfs_root_parms, if it exists.
*/
root_server_addr = root_nfs_parse_addr(nfs_root_parms);
return 1;
}
__setup("nfsroot=", nfs_root_setup);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);
/*
* Set up a console. Called via do_early_param() in init/main.c
* for each "console=" parameter in the boot command line.
*/
static int __init console_setup(char *str)
{
char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
char *s, *options, *brl_options = NULL;
int idx;
if (_braille_console_setup(&str, &brl_options))
return 1;
/*
* Decode str into name, index, options.
*/
if (str[0] >= '0' && str[0] <= '9') {
strcpy(buf, "ttyS");
strncpy(buf + 4, str, sizeof(buf) - 5);
} else {
strncpy(buf, str, sizeof(buf) - 1);
}
buf[sizeof(buf) - 1] = 0;
options = strchr(str, ',');
if (options)
*(options++) = 0;
#ifdef __sparc__
if (!strcmp(str, "ttya"))
strcpy(buf, "ttyS0");
if (!strcmp(str, "ttyb"))
strcpy(buf, "ttyS1");
#endif
for (s = buf; *s; s++)
if (isdigit(*s) || *s == ',')
break;
idx = simple_strtoul(s, NULL, 10);
*s = 0;
__add_preferred_console(buf, idx, options, brl_options);
console_set_on_cmdline = 1;
return 1;
}
__setup("console=", console_setup);这里因为我们的主体是调试，所以我么这里主要说console
通过前面我们知道给函数传进来的是val，也就是=后面的字符串。
上面这个console_setup的前面的判断_braille_console_setup，因为比较了brl肯定是通不过的，所以会继续执行
int _braille_console_setup(char **str, char **brl_options)
{
if (!strncmp(*str, "brl,", 4)) {
*brl_options = "";
*str += 4;
} else if (!strncmp(*str, "brl=", 4)) {
*brl_options = *str + 4;
*str = strchr(*brl_options, ',');
if (!*str) {
pr_err("need port name after brl=\n");
return -EINVAL;
}
*((*str)++) = 0;
}
return 0;
}
下面这句就是看传的第一个字符如果是数字字符的话，需要在前面加上ttyS，当然我们这里默认命令行是加了的。
还有就是在字符数组末尾添加结束符，在，的地方添加字符串结束符，同时把option指向之前，后面的那个字符，在我们这里就是115200的1的位置。
console=ttySAC2,115200 /*
* Decode str into name, index, options.
*/
if (str[0] >= '0' && str[0] <= '9') {
strcpy(buf, "ttyS");
strncpy(buf + 4, str, sizeof(buf) - 5);
} else {
strncpy(buf, str, sizeof(buf) - 1);
}
buf[sizeof(buf) - 1] = 0;
options = strchr(str, ',');
if (options)
*(options++) = 0;接下来就是，在console的参数中，找到字符为数字开始的地方，并把这个字符串转化为真正的数字，之后把转还后数字所在位置置为0。
for (s = buf; *s; s++)
if (isdigit(*s) || *s == ',')
break;
idx = simple_strtoul(s, NULL, 10);
*s = 0;
最后就是添加使用哪个console，和标记console已经被设置过。
__add_preferred_console(buf, idx, options, brl_options);
console_set_on_cmdline = 1;
添加首选的控制台。
这个函数做两件事，一个是检查是否当前要添加的控制台已经在内核定义的控制台数组添加过，已经添加过的话就不用再添加了。
如果没添加过，那就在console_cmdline 数组，下标从小到大找一个没使用的添加进去，最后就是把这个console的index标记上。
static int __add_preferred_console(char *name, int idx, char *options,
char *brl_options)
{
struct console_cmdline *c;
int i;
/*
* See if this tty is not yet registered, and
* if we have a slot free.
*/
for (i = 0, c = console_cmdline;
i < MAX_CMDLINECONSOLES && c->name[0];
i++, c++) {
if (strcmp(c->name, name) == 0 && c->index == idx) {
if (!brl_options)
preferred_console = i;
return 0;
}
}
if (i == MAX_CMDLINECONSOLES)
return -E2BIG;
if (!brl_options)
preferred_console = i;
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
braille_set_options(c, brl_options);
c->index = idx;
return 0;
}
可以看到我们的consiole=ttySAC2转换之后就是
console_cmdline数组的某一项中
name = "ttySAC"
index = 2
option = "115200"这里看一下，内核最大允许有8个控制台。
struct console_cmdline
{
char name[16]; /* Name of the driver */
int index; /* Minor dev. to use */
char *options; /* Options for the driver */
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
char *brl_options; /* Options for braille driver */
#endif
};
#define MAX_CMDLINECONSOLES 8
static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
到这里内核传参已经分析结束了。
我们助理主要就是把ttySAC2放到console_cmdline数组中，当然内核允许最大8个console，我们也可以传不止一个参数的。
接下来就是当真正的驱动函数注册的时候，注册console，同时如果注册的console和console_cmdline数组中的某一项的名字和index一样的话就表示匹配成功。此时对这个console做好标记表示已经可以用就可以了。
这里要说明的是console是一个非常复杂的驱动程序，层次会非常多，逻辑也是很乱，所以我不一定写的很清楚。