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1.1 root 1: /*
2: * 'fork.c' contains the help-routines for the 'fork' system call
3: * (see also system_call.s), and some misc functions ('verify_area').
4: * Fork is rather simple, once you get the hang of it, but the memory
5: * management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'
6: */
7: #include <errno.h>
8:
9: #include <linux/sched.h>
10: #include <linux/kernel.h>
11: #include <asm/segment.h>
12: #include <asm/system.h>
13:
14: extern void write_verify(unsigned long address);
15:
16: long last_pid=0;
17:
18: void verify_area(void * addr,int size)
19: {
20: unsigned long start;
21:
22: start = (unsigned long) addr;
23: size += start & 0xfff;
24: start &= 0xfffff000;
25: start += get_base(current->ldt[2]);
26: while (size>0) {
27: size -= 4096;
28: write_verify(start);
29: start += 4096;
30: }
31: }
32:
33: int copy_mem(int nr,struct task_struct * p)
34: {
35: unsigned long old_data_base,new_data_base,data_limit;
36: unsigned long old_code_base,new_code_base,code_limit;
37:
38: code_limit=get_limit(0x0f);
39: data_limit=get_limit(0x17);
40: old_code_base = get_base(current->ldt[1]);
41: old_data_base = get_base(current->ldt[2]);
42: if (old_data_base != old_code_base)
43: panic("We don't support separate I&D");
44: if (data_limit < code_limit)
45: panic("Bad data_limit");
46: new_data_base = new_code_base = nr * 0x4000000;
47: set_base(p->ldt[1],new_code_base);
48: set_base(p->ldt[2],new_data_base);
49: if (copy_page_tables(old_data_base,new_data_base,data_limit)) {
50: free_page_tables(new_data_base,data_limit);
51: return -ENOMEM;
52: }
53: return 0;
54: }
55:
56: /*
57: * Ok, this is the main fork-routine. It copies the system process
58: * information (task[nr]) and sets up the necessary registers. It
59: * also copies the data segment in it's entirety.
60: */
61: int copy_process(int nr,long ebp,long edi,long esi,long gs,long none,
62: long ebx,long ecx,long edx,
63: long fs,long es,long ds,
64: long eip,long cs,long eflags,long esp,long ss)
65: {
66: struct task_struct *p;
67: int i;
68: struct file *f;
69:
70: p = (struct task_struct *) get_free_page();
71: if (!p)
72: return -EAGAIN;
73: *p = *current; /* NOTE! this doesn't copy the supervisor stack */
74: p->state = TASK_RUNNING;
75: p->pid = last_pid;
76: p->father = current->pid;
77: p->counter = p->priority;
78: p->signal = 0;
79: p->alarm = 0;
80: p->leader = 0; /* process leadership doesn't inherit */
81: p->utime = p->stime = 0;
82: p->cutime = p->cstime = 0;
83: p->start_time = jiffies;
84: p->tss.back_link = 0;
85: p->tss.esp0 = PAGE_SIZE + (long) p;
86: p->tss.ss0 = 0x10;
87: p->tss.eip = eip;
88: p->tss.eflags = eflags;
89: p->tss.eax = 0;
90: p->tss.ecx = ecx;
91: p->tss.edx = edx;
92: p->tss.ebx = ebx;
93: p->tss.esp = esp;
94: p->tss.ebp = ebp;
95: p->tss.esi = esi;
96: p->tss.edi = edi;
97: p->tss.es = es & 0xffff;
98: p->tss.cs = cs & 0xffff;
99: p->tss.ss = ss & 0xffff;
100: p->tss.ds = ds & 0xffff;
101: p->tss.fs = fs & 0xffff;
102: p->tss.gs = gs & 0xffff;
103: p->tss.ldt = _LDT(nr);
104: p->tss.trace_bitmap = 0x80000000;
105: if (last_task_used_math == current)
106: __asm__("fnsave %0"::"m" (p->tss.i387));
107: if (copy_mem(nr,p)) {
108: free_page((long) p);
109: return -EAGAIN;
110: }
111: for (i=0; i<NR_OPEN;i++)
112: if (f=p->filp[i])
113: f->f_count++;
114: if (current->pwd)
115: current->pwd->i_count++;
116: if (current->root)
117: current->root->i_count++;
118: set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY,&(p->tss));
119: set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY,&(p->ldt));
120: task[nr] = p; /* do this last, just in case */
121: return last_pid;
122: }
123:
124: int find_empty_process(void)
125: {
126: int i;
127:
128: repeat:
129: if ((++last_pid)<0) last_pid=1;
130: for(i=0 ; i<NR_TASKS ; i++)
131: if (task[i] && task[i]->pid == last_pid) goto repeat;
132: for(i=1 ; i<NR_TASKS ; i++)
133: if (!task[i])
134: return i;
135: return -EAGAIN;
136: }
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