上一節我們分析的earlay的printk知識，本節主要分析一下在內核啓動後的printk的知識。
主要是通過下面函數實現的
after_dashes = parse_args("Booting kernel",
static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, NULL, &unknown_bootoption);
這裏又有一個段屬性，_param，通過下面方式定義
/* 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)
主要由下面這兩個結構體組成。
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，這個結構體中，.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)
我們已經知道了這裏是依次拿出cmdline中的每個命令和params中的進行比較，
/* 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;
}
要是相等會執行，會對參數檢測後，執行ops裏面的set函數。然後退出。
當然這個函數還有另一個作用就是不匹配不成功的情況下，執行handle_unknown函數。
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;
}
當然這裏的handle_unknown函數就是我們本次的重點了。
也就是cmdline中的每個命令，如果和__start___param段屬性中的所有都沒匹配成功，就會執行一次handle_unknown函數，在我們這裏也就是下面的這個unknown_bootoption函數。
/*
* 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;
}
這裏的傳參分爲三種，一種是過時的參數解析，一種是val表示傳的是環境變量，第二種是沒有val即爲NULL時，是傳的命令行參數。
我們這裏是設備樹傳過來的chosen裏面的命令行，一些命令行是過時的，一些則不是
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;
}
這個函數上一節分析過，在.init.setup段屬性中查找是否存這個cmdline傳過來的命令。
分爲earlay和非earlay，因爲earlay階段已經過去，這裏的都是普通的。
看一下我們的命令行參數有
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);
這裏因爲我們的主體是調試，所以我麼這裏主要說console
通過前面我們知道給函數傳進來的是val，也就是=後面的字符串。
上面這個console_setup的前面的判斷_braille_console_setup，因爲比較了brl肯定是通不過的，所以會繼續執行
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;
}
下面這句就是看傳的第一個字符如果是數字字符的話，需要在前面加上ttyS，當然我們這裏默認命令行是加了的。
還有就是在字符數組末尾添加結束符，在，的地方添加字符串結束符，同時把option指向之前，後面的那個字符，在我們這裏就是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;
接下來就是，在console的參數中，找到字符爲數字開始的地方，並把這個字符串轉化爲真正的數字，之後把轉還後數字所在位置置爲0。
for (s = buf; *s; s++)
if (isdigit(*s) || *s == ',')
break;
idx = simple_strtoul(s, NULL, 10);
*s = 0;
最後就是添加使用哪個console，和標記console已經被設置過。
__add_preferred_console(buf, idx, options, brl_options);
console_set_on_cmdline = 1;
添加首選的控制檯。
這個函數做兩件事，一個是檢查是否當前要添加的控制檯已經在內核定義的控制檯數組添加過，已經添加過的話就不用再添加了。
如果沒添加過，那就在console_cmdline 數組，下標從小到大找一個沒使用的添加進去，最後就是把這個console的index標記上。
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;
}
可以看到我們的consiole=ttySAC2轉換之後就是
console_cmdline數組的某一項中
name = "ttySAC"
index = 2
option = "115200"
這裏看一下，內核最大允許有8個控制檯。
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];
到這裏內核傳參已經分析結束了。
我們助理主要就是把ttySAC2放到console_cmdline數組中，當然內核允許最大8個console，我們也可以傳不止一個參數的。
接下來就是當真正的驅動函數註冊的時候，註冊console，同時如果註冊的console和console_cmdline數組中的某一項的名字和index一樣的話就表示匹配成功。此時對這個console做好標記表示已經可以用就可以了。
這裏要說明的是console是一個非常複雜的驅動程序，層次會非常多，邏輯也是很亂，所以我不一定寫的很清楚。