每一个任务都有一个mm_struct结构管理任务内存空间，init_mm是内核的mm_struct，设置* pgd=swapper_pg_dir，swapper_pg_dir是内核的页目录，在arm体系结构有16k，所以init_mm定义了整个 kernel的内存空间，下面我们会碰到内核线程，所有的内核线程都使用内核空间，拥有和内核同样的访问权限。对于内存管理后面再做详细分析。
mm_struct结构定义在include/linux/mm_types.h中，
struct mm_struct {
struct vm_area_struct * mmap; /* list of VMAs */
struct rb_root mm_rb;
struct vm_area_struct * mmap_cache; /* last find_vma result */
#ifdef CONFIG_MMU
unsigned long (*get_unmapped_area) (struct file *filp,
unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags);
void (*unmap_area) (struct mm_struct *mm, unsigned long addr);
#endif
unsigned long mmap_base; /* base of mmap area */
unsigned long task_size; /* size of task vm space */
unsigned long cached_hole_size; /* if non-zero, the largest hole below free_area_cache */
unsigned long free_area_cache; /* first hole of size cached_hole_size or larger */
pgd_t * pgd;
atomic_t mm_users; /* How many users with user space? */
atomic_t mm_count; /* How many references to "struct mm_struct" (users count as 1) */
int map_count; /* number of VMAs */
struct rw_semaphore mmap_sem;
spinlock_t page_table_lock; /* Protects page tables and some counters */
struct list_head mmlist; /* List of maybe swapped mm‘s. These are globally strung
* together off init_mm.mmlist, and are protected
* by mmlist_lock
*/
unsigned long hiwater_rss; /* High-watermark of RSS usage */
unsigned long hiwater_vm; /* High-water virtual memory usage */
unsigned long total_vm, locked_vm, shared_vm, exec_vm;
unsigned long stack_vm, reserved_vm, def_flags, nr_ptes; unsigned long start_code, end_code, start_data, end_data;
unsigned long start_brk, brk, start_stack;
unsigned long arg_start, arg_end, env_start, env_end;
unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
/*
* Special counters, in some configurations protected by the
* page_table_lock, in other configurations by being atomic.
*/
struct mm_rss_stat rss_stat;
struct linux_binfmt *binfmt;
cpumask_t cpu_vm_mask;
/* Architecture-specific MM context */
mm_context_t context;
/* Swap token stuff */
/*
* Last value of global fault stamp as seen by this process.
* In other words, this value gives an indication of how long
* it has been since this task got the token.
* Look at mm/thrash.c
*/
unsigned int faultstamp;
unsigned int token_priority;
unsigned int last_interval;
unsigned long flags; /* Must use atomic bitops to access the bits */
struct core_state *core_state; /* coredumping support */
#ifdef CONFIG_AIO
spinlock_t ioctx_lock;
struct hlist_head ioctx_list;
#endif
#ifdef CONFIG_MM_OWNER
/*
* "owner" points to a task that is regarded as the canonical
* user/owner of this mm. All of the following must be true in
* order for it to be changed:
*
* current == mm->owner
* current->mm != mm
* new_owner->mm == mm
* new_owner->alloc_lock is held
*/
struct task_struct *owner;
#endif
#ifdef CONFIG_PROC_FS
/* store ref to file /proc//exe symlink points to */
struct file *exe_file;
unsigned long num_exe_file_vmas;
#endif
#ifdef CONFIG_MMU_NOTIFIER
struct mmu_notifier_mm *mmu_notifier_mm;
#endif
};
/* Arch code calls this early on, or if not, just before other parsing. */
void __init parse_early_param(void)
{
static __initdata int done = 0;
static __initdata char tmp_cmdline[COMMAND_LINE_SIZE];
if (done)
return;
/* All fall through to do_early_param. */
strlcpy(tmp_cmdline, boot_command_line, COMMAND_LINE_SIZE);
parse_early_options(tmp_cmdline);
done = 1;
}
在上面我们可以看到最终调用的是 parse_args("early options", cmdline, NULL, 0, do_early_param);它调用do_early_param函数处理early_param定义的参数函数
这个函数还另一种调用形式
parse_args("Booting kernel", static_command_line, __start___param,_stop___param - __start___param,&unknown_bootoption); 它调用unknown_bootoption函数处理__setup定义的参数，unknown_bootoption函数在init/main.c中定义如下：
static int __init unknown_bootoption(char *param, char *val)
{
/* Change NUL term back to "=", to make "param" the whole string. */
if (val) {
/* param=val or param="val"? */
if (val == param+strlen(param)+1)
val[-1] = ‘=‘;
else if (val == param+strlen(param)+2) {
val[-2] = ‘=‘;
memmove(val-1, val, strlen(val)+1);
val--;
} else
BUG();
}
/* Handle obsolete-style parameters */
if (obsolete_checksetup(param))
return 0;
if (val) {
/* Environment option */
unsigned int i;
for (i = 0; envp_init[i]; i++) {
if (i == MAX_INIT_ENVS) {
panic_later = "Too many boot env vars at `%s‘";
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 = "Too many boot init vars at `%s‘";
panic_param = param;
}
}
argv_init[i] = param;
}
return 0;
}
在这个函数中它调用了obsolete_checksetup函数，该函数也定义在init/main.c中
static int __init obsolete_checksetup(char *line)
{
const 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 (line[n] == ‘\0‘ || line[n] == ‘=‘)
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;
}
我们再来看一下do_early_param函数，它在init/main.c中
static int __init do_early_param(char *param, char *val)
{
const struct obs_kernel_param *p;
这里的__setup_start和_-setup_end分别是.init.setup段的起始和结束的地址
for (p = __setup_start; p < __setup_end; p++) { 如果没有early标志则跳过
if ((p->early && strcmp(param, p->str) == 0) ||
(strcmp(param, "console") == 0 &&
strcmp(p->str, "earlycon") == 0)
) {
if (p->setup_func(val) != 0) 调用处理函数
printk(KERN_WARNING
"Malformed early option ‘%s‘\n", param);
}
}
/* We accept everything at this stage. */
return 0;
}
parse_args在kernel/params.c中定义，注意它与前面讲到的parse_args区别。
/* Args looks like "foo=bar,bar2 baz=fuz wiz". */
int parse_args(const char *name,
char *args,
const struct kernel_param *params,
unsigned num,
int (*unknown)(char *param, char *val))
{
char *param, *val;
DEBUGP("Parsing ARGS: %s\n", args);
/* Chew leading spaces */
args = skip_spaces(args);
while (*args) {
int ret;
int irq_was_disabled;
args = next_arg(args, ¶m, &val);
irq_was_disabled = irqs_disabled();
ret = parse_one(param, val, params, num, unknown);
if (irq_was_disabled && !irqs_disabled()) {
printk(KERN_WARNING "parse_args(): option ‘%s‘ enabled "
"irq‘s!\n", param);
}
switch (ret) {
case -ENOENT:
printk(KERN_ERR "%s: Unknown parameter `%s‘\n",
name, param);
return ret;
case -ENOSPC:
printk(KERN_ERR
"%s: `%s‘ too large for parameter `%s‘\n",
name, val ?: "", param);
return ret;
case 0:
break;
default:
printk(KERN_ERR
"%s: `%s‘ invalid for parameter `%s‘\n",
name, val ?: "", param);
return ret;
}
}
struct kernel_param_ops {
/* Returns 0, or -errno. arg is in kp->arg. */
int (*set)(const char *val, const struct kernel_param *kp);设置参数的函数
/* Returns length written or -errno. Buffer is 4k (ie. be short!) */
int (*get)(char *buffer, const struct kernel_param *kp);读取参数的函数
/* Optional function to free kp->arg when module unloaded. */
void (*free)(void *arg);
};
/* Flag bits for kernel_param.flags */
#define KPARAM_ISBOOL 2
/* Special one for strings we want to copy into */
struct kparam_string {
unsigned int maxlen;
char *string;
};
/* Special one for arrays */
struct kparam_array
{
unsigned int max;
unsigned int *num;
const struct kernel_param_ops *ops;
unsigned int elemsize;
void *elem;
};
接下来来看parse_one函数，其中early和一般的pase都是通过这个函数来解析：
kernel/params.c
static inline char dash2underscore(char c)
{
if (c == ‘-‘)
return ‘_‘;
return c;
}
static inline int parameq(const char *input, const char *paramname)
{
unsigned int i;
for (i = 0; dash2underscore(input[i]) == paramname[i]; i++)
if (input[i] == ‘\0‘)
return 1;
return 0;
}
static int parse_one(char *param,
char *val,
const struct kernel_param *params,
unsigned num_params,
int (*handle_unknown)(char *param, char *val))
{
unsigned int i;
int err;
如果是early_param则直接跳过这步，而非early的，则要通过这步来设置一些内置模块的参数。
/* Find parameter */
for (i = 0; i < num_params; i++) {
if (parameq(param, params[i].name)) {
/* Noone handled NULL, so do it here. */
if (!val && params[i].ops->set != param_set_bool) 调用参数设置函数来设置对应的参数。
return -EINVAL;
DEBUGP("They are equal! Calling %p\n",
params[i].ops->set);
mutex_lock(¶m_lock);
err = params[i].ops->set(val, ¶ms[i]);
mutex_unlock(¶m_lock);
return err;
}
}
