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介绍linux下文件和设备编程

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<hr><br><A NAME="I409" ID="I409"></A><center><b><font size=+2>sched.c</font></b></center><br>
|schedule<br>
&nbsp;&nbsp; |do_softirq // manages post-IRQ work<br>
&nbsp;&nbsp; |for each task<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |calculate counter<br>
&nbsp;&nbsp; |prepare_to__switch // does anything<br>
&nbsp;&nbsp; |switch_mm // change Memory context (change CR3 value)<br>
&nbsp;&nbsp; |switch_to (assembler)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |SAVE ESP<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |RESTORE future_ESP<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |SAVE EIP<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |push future_EIP *** push parameter as we did a call<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |jmp __switch_to (it does some TSS work)<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |__switch_to()<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ..<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |ret *** ret from call using future_EIP in place of call address<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; new_task<p>
<br>
/*<br>
* 'sched.c' is the main kernel file. It contains scheduling primitives<br>
* (sleep_on, wakeup, schedule etc) as well as a number of simple system<br>
* call functions (type getpid(), which just extracts a field from<br>
* current-task<br>
*/<br>
#include<br>
#include<br>
#include<br>
#include<br>
#include<br>
#include<br>
#include<br>
#define LATCH (1193180/HZ)<br>
extern void mem_use(void);<br>
extern int timer_interrupt(void);<br>
extern int system_call(void);<br>
union task_union {<br>
struct task_struct task;<br>
char stack[PAGE_SIZE];<br>
};<br>
static union task_union init_task = {INIT_TASK,};<br>
long volatile jiffies=0;<br>
long startup_time=0;<br>
struct task_struct *current = &amp;(init_task.task), *last_task_used_math =<br>
NULL;<br>
struct task_struct * task[NR_TASKS] = {&amp;(init_task.task), };<br>
long user_stack [ PAGE_SIZE&gt;&gt;2 ] ;<br>
struct {<br>
long * a;<br>
short b;<br>
} stack_start = { &amp; user_stack [PAGE_SIZE&gt;&gt;2] , 0x10 };<br>
/*<br>
* 'math_state_restore()' saves the current math information in the<br>
* old math state array, and gets the new ones from the current task<br>
*/<br>
void math_state_restore() @@协处理器状态保存<br>
{<br>
if (last_task_used_math)<br>
__asm__(&quot;fnsave %0&quot;::&quot;m&quot; (last_task_used_math-&gt;tss.i387));<br>
if (current-&gt;used_math)<br>
__asm__(&quot;frstor %0&quot;::&quot;m&quot; (current-&gt;tss.i387));<br>
else {<br>
__asm__(&quot;fninit&quot;::);<br>
current-&gt;used_math=1;<br>
}<br>
last_task_used_math=current;<br>
}<br>
/*<br>
* 'schedule()' is the scheduler function. This is GOOD CODE! There<br>
* probably won't be any reason to change this, as it should work well<br>
* in all circumstances (ie gives IO-bound processes good response etc).<br>
* The one thing you might take a look at is the signal-handler code<br>
here.<br>
*<br>
* NOTE!! Task 0 is the 'idle' task, which gets called when no other<br>
* tasks can run. It can not be killed, and it cannot sleep. The 'state'<br>
* information in task[0] is never used.<br>
*/<br>
void schedule(void)<br>
{<br>
int i,next,c;<br>
struct task_struct ** p;<br>
/* check alarm, wake up any interruptible tasks that have got a signal<br>
*/<br>
for(p = &amp;LAST_TASK ; p &gt; &amp;FIRST_TASK ; --p)<br>
if (*p) {<br>
if ((*p)-&gt;alarm &amp;&amp; (*p)-&gt;alarm &lt; jiffies) {<br>
@@??<br>
(*p)-&gt;signal |= (1&lt;&lt;(SIGALRM-1));@@14-1<br>
(*p)-&gt;alarm = 0;<br>
}<br>
if ((*p)-&gt;signal &amp;&amp; (*p)-&gt;state==TASK_INTERRUPTIBLE)<br>
(*p)-&gt;state=TASK_RUNNING;<br>
}<br>
@@ task 1 如何变为TASK_RUNNING??signal 如何得到,alarm如何变非0且 /* this is the<br>
scheduler proper: */<br>
@@操作系统最重要的函数，调度算法<br>
@@这个循环要找到一个可运行的任务才能退出,会死在这吗?即如没有一个可运行<br>
while (1) {<br>
c = -1;<br>
next = 0;<br>
i = NR_TASKS;<br>
p = &amp;task[NR_TASKS];<br>
while (--i) {<br>
if (!*--p)<br>
continue;<br>
if ((*p)-&gt;state == TASK_RUNNING &amp;&amp; (*p)-&gt;counter &gt; c)<br>
c = (*p)-&gt;counter, next = i;<br>
}<br>
if (c) break; @@记数大于零<br>
for(p = &amp;LAST_TASK ; p &gt; &amp;FIRST_TASK ; --p)<br>
if (*p)<br>
(*p)-&gt;counter = ((*p)-&gt;counter &gt;&gt; 1) +<br>
(*p)-&gt;priority;<br>
}<br>
switch_to(next);<br>
}<br>
int sys_pause(void)<br>
{<br>
current-&gt;state = TASK_INTERRUPTIBLE; @@任务可中断<br>
schedule();<br>
return 0;<br>
}<br>
void sleep_on(struct task_struct **p)<br>
{<br>
struct task_struct *tmp;<br>
if (!p)<br>
return;<br>
if (current == &amp;(init_task.task))<br>
panic(&quot;task[0] trying to sleep&quot;);<br>
tmp = *p;<br>
*p = current;<br>
current-&gt;state = TASK_UNINTERRUPTIBLE;<br>
schedule();<br>
if (tmp) @@激活p，什么时候回来？唤醒上次睡眠的进程<br>
tmp-&gt;state=0;<br>
}<br>
void interruptible_sleep_on(struct task_struct **p)<br>
{<br>
struct task_struct *tmp;<br>
if (!p)<br>
return;<br>
if (current == &amp;(init_task.task))<br>
panic(&quot;task[0] trying to sleep&quot;);<br>
tmp=*p;<br>
*p=current;<br>
repeat: current-&gt;state = TASK_INTERRUPTIBLE;<br>
schedule();<br>
if (*p &amp;&amp; *p != current) {<br>
(**p).state=0;<br>
goto repeat;<br>
}<br>
@@好象下不来<br>
*p=NULL;<br>
if (tmp)<br>
tmp-&gt;state=0;<br>
}<br>
void wake_up(struct task_struct **p)<br>
{<br>
if (p &amp;&amp; *p) {<br>
(**p).state=0; @@唤醒该进程running<br>
*p=NULL; @@睡眠栈为0<br>
}<br>
}<br>
void do_timer(long cpl) @@定时调度<br>
{<br>
if (cpl)<br>
current-&gt;utime++; @@用户态时间加一<br>
else<br>
current-&gt;stime++; @@系统态时间加一<br>
if ((--current-&gt;counter)&gt;0) return; @@当前记数减一<br>
current-&gt;counter=0;<br>
if (!cpl) return;<br>
schedule();<br>
}<br>
int sys_alarm(long seconds)<br>
{<br>
current-&gt;alarm = (seconds&gt;0)?(jiffies+HZ*seconds):0;<br>
return seconds;<br>
}<br>
int sys_getpid(void)<br>
{<br>
return current-&gt;pid;<br>
}<br>
int sys_getppid(void)<br>
{<br>
return current-&gt;father;<br>
}<br>
int sys_getuid(void)<br>
{<br>
return current-&gt;uid;<br>
}<br>
int sys_geteuid(void)<br>
{<br>
return current-&gt;euid;<br>
}<br>