linux-schec.c
/*
* linux/kernel/sched.c
* //－－内核中有关任务(进程)调度管理的程序
* (C) 1991 Linus Torvalds
*/
/*
* 'sched.c' is the main kernel file. It contains scheduling primitives
* (sleep_on, wakeup, schedule etc) as well as a number of simple system
* call functions (type getpid(), which just extracts a field from
* current-task
*/
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/sys.h>
#include <linux/fdreg.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/segment.h>
#include <signal.h>
#define _S(nr) (1<<((nr)-1)) //－－左移nr-1位
#define _BLOCKABLE (~(_S(SIGKILL) | _S(SIGSTOP)))
void show_task(int nr,struct task_struct * p)
{ //－－内核调试函数，显示任务号nr的进程号，进程状态和内核栈空闲字节数
int i,j = 4096-sizeof(struct task_struct);
printk("%d: pid=%d, state=%d, father=%d, child=%d, ",nr,p->pid,
p->state, p->p_pptr->pid, p->p_cptr ? p->p_cptr->pid : -1);
i=0;
while (i<j && !((char *)(p+1))[i]) //－－检测0的字节数
i++;
printk("%d/%d chars free in kstack/n/r",i,j);
printk(" PC=%08X.", *(1019 + (unsigned long *) p));
if (p->p_ysptr || p->p_osptr)
printk(" Younger sib=%d, older sib=%d/n/r",
p->p_ysptr ? p->p_ysptr->pid : -1,
p->p_osptr ? p->p_osptr->pid : -1);
else
printk("/n/r");
}
void show_state(void)
{
int i;
printk("/rTask-info:/n/r");
for (i=0;i<NR_TASKS;i++) //－－NR_TASKS系统能容纳的最大进程数(64)
if (task[i])
show_task(i,task[i]);
}
#define LATCH (1193180/HZ) //－－8253时钟初始值
extern void mem_use(void); //－－没有任何地方定义和引用该函数
extern int timer_interrupt(void);
extern int system_call(void);
union task_union { //－－任务内核态堆栈结构
struct task_struct task;
char stack[PAGE_SIZE];
};
static union task_union init_task = {INIT_TASK,};
unsigned long volatile jiffies=0;
unsigned long startup_time=0;
int jiffies_offset = 0; /* # clock ticks to add to get "true
time". Should always be less than
1 second's worth. For time fanatics
who like to syncronize their machines
to WWV :-) */
struct task_struct *current = &(init_task.task);
struct task_struct *last_task_used_math = NULL;
struct task_struct * task[NR_TASKS] = {&(init_task.task), };
long user_stack [ PAGE_SIZE>>2 ] ; //－－定义用户堆栈
struct {
long * a;
short b;
} stack_start = { & user_stack [PAGE_SIZE>>2] , 0x10 };
/*
* 'math_state_restore()' saves the current math information in the
* old math state array, and gets the new ones from the current task
*/
void math_state_restore() //－－保存旧的任务，将当前任务的协处理器内容加载进协处理器
{
if (last_task_used_math == current)
return;
__asm__("fwait");
if (last_task_used_math) {
__asm__("fnsave %0"::"m" (last_task_used_math->tss.i387));
}
last_task_used_math=current;
if (current->used_math) {
__asm__("frstor %0"::"m" (current->tss.i387));
} else {
__asm__("fninit"::);
current->used_math=1;
}
}
/*
* 'schedule()' is the scheduler function. This is GOOD CODE! There
* probably won't be any reason to change this, as it should work well
* in all circumstances (ie gives IO-bound processes good response etc).
* The one thing you might take a look at is the signal-handler code here.
*
* NOTE!! Task 0 is the 'idle' task, which gets called when no other
* tasks can run. It can not be killed, and it cannot sleep. The 'state'
* information in task[0] is never used.
*/
void schedule(void) //－－调度函数
{
int i,next,c;
struct task_struct ** p;
/* check alarm, wake up any interruptible tasks that have got a signal */
for(p = &LAST_TASK ; p > &FIRST_TASK ; --p) //－－从最后一个任务开始循环检测
if (*p) {
if ((*p)->timeout && (*p)->timeout < jiffies) {
(*p)->timeout = 0; //－－超时定时器复位
if ((*p)->state == TASK_INTERRUPTIBLE)
(*p)->state = TASK_RUNNING; //－－置为就绪态
}
if ((*p)->alarm && (*p)->alarm < jiffies) {
(*p)->signal |= (1<<(SIGALRM-1));
(*p)->alarm = 0; //－－alarm定时值
}
if (((*p)->signal & ~(_BLOCKABLE & (*p)->blocked)) &&
(*p)->state==TASK_INTERRUPTIBLE)
(*p)->state=TASK_RUNNING; //－－信号位图
}
/* this is the scheduler proper: */
while (1) {
c = -1;
next = 0;
i = NR_TASKS;
p = &task[NR_TASKS];
while (--i) { //－－找counter值最大的，即运行时间最短的
if (!*--p)
continue;
if ((*p)->state == TASK_RUNNING && (*p)->counter > c)
c = (*p)->counter, next = i;
}
if (c) break; //－－若counter=0，则重置counter=priority
for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)
if (*p)
(*p)->counter = ((*p)->counter >> 1) +
(*p)->priority; //－－计算counter=counter/2+priority;
}
switch_to(next); //－－切换到下一个任务
}
int sys_pause(void) //－－未完全实现的函数
{
current->state = TASK_INTERRUPTIBLE;
schedule();
return 0;
}
static inline void __sleep_on(struct task_struct **p, int state)
{
struct task_struct *tmp; //－－置当前任务为指定的睡眠状态
if (!p)
return;
if (current == &(init_task.task))
panic("task[0] trying to sleep");
tmp = *p;
*p = current;
current->state = state;
repeat: schedule();
if (*p && *p != current) {
(**p).state = 0;
current->state = TASK_UNINTERRUPTIBLE;
goto repeat;
}
if (!*p)
printk("Warning: *P = NULL/n/r");
if (*p = tmp)
tmp->state=0;
}
void interruptible_sleep_on(struct task_struct **p) //－－置当前任务为可中断的等待状态
{
__sleep_on(p,TASK_INTERRUPTIBLE);
}
void sleep_on(struct task_struct **p) //－－置当前任务为不可中断的等待状态
{
__sleep_on(p,TASK_UNINTERRUPTIBLE);
}
void wake_up(struct task_struct **p) //－－唤醒*p指向的任务
{
if (p && *p) {
if ((**p).state == TASK_STOPPED)
printk("wake_up: TASK_STOPPED");
if ((**p).state == TASK_ZOMBIE)
printk("wake_up: TASK_ZOMBIE");
(**p).state=0;
}
}
/*
* OK, here are some floppy things that shouldn't be in the kernel
* proper. They are here because the floppy needs a timer, and this
* was the easiest way of doing it.
*/ //－－下面为一些有关软盘的子程序，220-281为处理软驱定时
static struct task_struct * wait_motor[4] = {NULL,NULL,NULL,NULL};
static int mon_timer[4]={0,0,0,0};
static int moff_timer[4]={0,0,0,0};
unsigned char current_DOR = 0x0C;
int ticks_to_floppy_on(unsigned int nr) //－－设置moff_timer[]和mon_timer[]
{
extern unsigned char selected;
unsigned char mask = 0x10 << nr;
if (nr>3)
panic("floppy_on: nr>3");
moff_timer[nr]=10000; /* 100 s = very big :-) */
cli(); /* use floppy_off to turn it off */
mask |= current_DOR;
if (!selected) {
mask &= 0xFC;
mask |= nr;
}
if (mask != current_DOR) {
outb(mask,FD_DOR);
if ((mask ^ current_DOR) & 0xf0)
mon_timer[nr] = HZ/2;
else if (mon_timer[nr] < 2)
mon_timer[nr] = 2;
current_DOR = mask;
}
sti();
return mon_timer[nr];
}
void floppy_on(unsigned int nr) //－－等待马达启动
{
cli();
while (ticks_to_floppy_on(nr))
sleep_on(nr+wait_motor);
sti();
}
void floppy_off(unsigned int nr) //－－停转等待时间
{
moff_timer[nr]=3*HZ;
}
void do_floppy_timer(void) //－－设置mon_timer[]和moff_timer[]
{
int i;
unsigned char mask = 0x10;
for (i=0 ; i<4 ; i++,mask <<= 1) {
if (!(mask & current_DOR))
continue;
if (mon_timer[i]) {
if (!--mon_timer[i])
wake_up(i+wait_motor);
} else if (!moff_timer[i]) {
current_DOR &= ~mask;
outb(current_DOR,FD_DOR);
} else
moff_timer[i]--;
}
}
//－－下面是关于定时器的代码
#define TIME_REQUESTS 64
static struct timer_list { //－－定时器链表结构和定时器数组
long jiffies;
void (*fn)(); //－－定时处理函数
struct timer_list * next;
} timer_list[TIME_REQUESTS], * next_timer = NULL;
void add_timer(long jiffies, void (*fn)(void)) //－－增加定时器
{
struct timer_list * p;
if (!fn)
return;
cli();
if (jiffies <= 0)
(fn)();
else {
for (p = timer_list ; p < timer_list + TIME_REQUESTS ; p++)
if (!p->fn)
break;
if (p >= timer_list + TIME_REQUESTS)
panic("No more time requests free");
p->fn = fn;
p->jiffies = jiffies;
p->next = next_timer;
next_timer = p;
while (p->next && p->next->jiffies < p->jiffies) {
p->jiffies -= p->next->jiffies;
fn = p->fn;
p->fn = p->next->fn;
p->next->fn = fn;
jiffies = p->jiffies;
p->jiffies = p->next->jiffies;
p->next->jiffies = jiffies;
p = p->next;
}
}
sti();
}
void do_timer(long cpl) //－－时钟中断处理程序
{
static int blanked = 0;
if (blankcount || !blankinterval) { //－－判黑屏超时
if (blanked)
unblank_screen();
if (blankcount)
blankcount--;
blanked = 0;
} else if (!blanked) {
blank_screen();
blanked = 1;
}
if (hd_timeout) //－－处理硬盘操作超时
if (!--hd_timeout)
hd_times_out();
if (beepcount) //－－发声计数
if (!--beepcount)
sysbeepstop();
if (cpl) //－－cpl=0为超级用户，cpl>0为普通用户
current->utime++;
else
current->stime++;
if (next_timer) { //－－定时器链表处理
next_timer->jiffies--;
while (next_timer && next_timer->jiffies <= 0) {
void (*fn)(void);
fn = next_timer->fn;
next_timer->fn = NULL;
next_timer = next_timer->next;
(fn)();
}
}
if (current_DOR & 0xf0)
do_floppy_timer();
if ((--current->counter)>0) return;
current->counter=0;
if (!cpl) return;
schedule();
}
int sys_alarm(long seconds) //－－系统调用功能，设置报警时间值
{
int old = current->alarm;
if (old)
old = (old - jiffies) / HZ;
current->alarm = (seconds>0)?(jiffies+HZ*seconds):0;
return (old);
}
int sys_getpid(void)
{
return current->pid;
}
int sys_getppid(void)
{
return current->p_pptr->pid;
}
int sys_getuid(void)
{
return current->uid;
}
int sys_geteuid(void)
{
return current->euid;
}
int sys_getgid(void)
{
return current->gid;
}
int sys_getegid(void)
{
return current->egid;
}
int sys_nice(long increment) //－－降低对CPU的使用优先权
{
if (current->priority-increment>0)
current->priority -= increment;
return 0;
}
void sched_init(void) //－－内核调度程序的初始化子程序
{
int i;
struct desc_struct * p;
if (sizeof(struct sigaction) != 16)
panic("Struct sigaction MUST be 16 bytes");
set_tss_desc(gdt+FIRST_TSS_ENTRY,&(init_task.task.tss)); //－－全局描述符表中设置初始任务0的
set_ldt_desc(gdt+FIRST_LDT_ENTRY,&(init_task.task.ldt)); //－－任务状态段描述符和局部数据表描述符
p = gdt+2+FIRST_TSS_ENTRY;
for(i=1;i<NR_TASKS;i++) { //－－清任务数组和描述符表选项
task[i] = NULL;
p->a=p->b=0;
p++;
p->a=p->b=0;
p++;
}
/* Clear NT, so that we won't have troubles with that later on */
__asm__("pushfl ; andl $0xffffbfff,(%esp) ; popfl"); //－－清除标志寄存器的NT位
ltr(0); //－－将任务0的TSS段段选择符加载到任务寄存器tr上
lldt(0);
outb_p(0x36,0x43); /* binary, mode 3, LSB/MSB, ch 0 */
outb_p(LATCH & 0xff , 0x40); /* LSB */ //－－初始化8253寄存器
outb(LATCH >> 8 , 0x40); /* MSB */
set_intr_gate(0x20,&timer_interrupt); //－－设置时钟中断处理程序句柄
outb(inb_p(0x21)&~0x01,0x21);
set_system_gate(0x80,&system_call);
}
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