2024年4月1日发(作者：)

linux源代码-fork.c源代码

/*

* linux/kernel/fork.c

* //－－fork()用于创建子进程

* (C) 1991 Linus Torvalds

*/

/*

* 'fork.c' contains the help-routines for the 'fork' system call

* (see also system_call.s), and some misc functions ('verify_area').

* Fork is rather simple, once you get the hang of it, but the memory

* management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'

*/

#include

#include

#include

#include

#include

//－－写页面验证，若页面不可写，则复制页面

extern void write_verify(unsigned long address);

long last_pid=0;

//－－进程空间区域写前验证函数

void verify_area(void * addr,int size)

{

unsigned long start;

start = (unsigned long) addr;

size += start & 0xfff;

start &= 0xfffff000;

start += get_base(current->ldt[2]); //－－逻辑地址到线性地址的转换

while (size>0) {

size -= 4096;

write_verify(start);

start += 4096;

}

}

int copy_mem(int nr,struct task_struct * p) //－－复制内存页表

{ //－－由于采用写时复制技术，这里只复制目录和页

表项，不分配内存

unsigned long old_data_base,new_data_base,data_limit;

unsigned long old_code_base,new_code_base,code_limit;

code_limit=get_limit(0x0f); //－－取段限长

data_limit=get_limit(0x17);

old_code_base = get_base(current->ldt[1]);

old_data_base = get_base(current->ldt[2]);

if (old_data_base != old_code_base)

panic("We don't support separate I&D");

if (data_limit < code_limit)

panic("Bad data_limit");

new_data_base = new_code_base = nr * TASK_SIZE;

p->start_code = new_code_base;

set_base(p->ldt[1],new_code_base);

set_base(p->ldt[2],new_data_base);

if (copy_page_tables(old_data_base,new_data_base,data_limit)) { //－－复

制页表

free_page_tables(new_data_base,data_limit);

return -ENOMEM;

}

return 0;

}

/*

* Ok, this is the main fork-routine. It copies the system process

* information (task[nr]) and sets up the necessary registers. It

* also copies the data segment in it's entirety.

*/ //－－fork()子程序，它复制系统进程信息，设置寄存器，

复制数据段(代码段)

int copy_process(int nr,long ebp,long edi,long esi,long gs,long none,

long ebx,long ecx,long edx, long orig_eax,

long fs,long es,long ds,

long eip,long cs,long eflags,long esp,long ss) //－－复制进程

{

struct task_struct *p;

int i;

struct file *f;

p = (struct task_struct *) get_free_page(); //－－为新任务数据结构分配

内存

if (!p)

return -EAGAIN;

task[nr] = p;

*p = *current; /* NOTE! this doesn't copy the supervisor stack */

p->state = TASK_UNINTERRUPTIBLE;

p->pid = last_pid;

p->counter = p->priority;

p->signal = 0;

p->alarm = 0;

p->leader = 0; /* process leadership doesn't inherit */

p->utime = p->stime = 0;

p->cutime = p->cstime = 0;

p->start_time = jiffies;

p->_link = 0;

p->0 = PAGE_SIZE + (long) p;

p->0 = 0x10;

p-> = eip;

p-> = eflags;

p-> = 0;

p-> = ecx;

p-> = edx;

p-> = ebx;

p-> = esp;

p-> = ebp;

p-> = esi;

p-> = edi;

p-> = es & 0xffff;

p-> = cs & 0xffff;

p-> = ss & 0xffff;

p-> = ds & 0xffff;

p-> = fs & 0xffff;

p-> = gs & 0xffff;

p-> = _LDT(nr);

p->_bitmap = 0x80000000;

if (last_task_used_math == current)

__asm__("clts ; fnsave %0 ; frstor %0"::"m" (p->tss.i387));

if (copy_mem(nr,p)) {

task[nr] = NULL;

free_page((long) p);

return -EAGAIN;

}

for (i=0; i

对应文件的打开次数增1

if (f=p->filp[i])

f->f_count++;

if (current->pwd)

current->pwd->i_count++;

if (current->root)

current->root->i_count++;

if (current->executable)

current->executable->i_count++;

if (current->library)

current->library->i_count++;

set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY,&(p->tss)); //－－在GDT表中

设置新任务的TSS和LDT

set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY,&(p->ldt));

p->p_pptr = current;

p->p_cptr = 0;

p->p_ysptr = 0;

p->p_osptr = current->p_cptr;

if (p->p_osptr)

p->p_osptr->p_ysptr = p;

current->p_cptr = p;

p->state = TASK_RUNNING; /* do this last, just in case */

return last_pid;

}

int find_empty_process(void) //－－为新进程取得不重复的进程号

last_pid

{

int i;

repeat:

if ((++last_pid)<0) last_pid=1;

for(i=0 ; i

if (task[i] && ((task[i]->pid == last_pid) ||

(task[i]->pgrp == last_pid)))

goto repeat;

for(i=1 ; i

if (!task[i])

return i;

return -EAGAIN;

}