1 files changed, 136 insertions, 0 deletions
diff --git a/linux/kernel/fork.c b/linux/kernel/fork.c
new file mode 100644
index 0000000..70f9ddd
--- /dev/null
+++ b/linux/kernel/fork.c
@@ -0,0 +1,136 @@
+/*
+ *  '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 <errno.h>
+
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <asm/segment.h>
+#include <asm/system.h>
+
+extern void write_verify(unsigned long address);
+
+long last_pid=0;
+
+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]);
+	while (size>0) {
+		size -= 4096;
+		write_verify(start);
+		start += 4096;
+	}
+}
+
+int copy_mem(int nr,struct task_struct * p)
+{
+	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);
+	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 * 0x4000000;
+	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)) {
+		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.
+ */
+int copy_process(int nr,long ebp,long edi,long esi,long gs,long none,
+		long ebx,long ecx,long edx,
+		long fs,long es,long ds,
+		long eip,long cs,long eflags,long esp,long ss)
+{
+	struct task_struct *p;
+	int i;
+	struct file *f;
+
+	p = (struct task_struct *) get_free_page();
+	if (!p)
+		return -EAGAIN;
+	*p = *current;	/* NOTE! this doesn't copy the supervisor stack */
+	p->state = TASK_RUNNING;
+	p->pid = last_pid;
+	p->father = current->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->tss.back_link = 0;
+	p->tss.esp0 = PAGE_SIZE + (long) p;
+	p->tss.ss0 = 0x10;
+	p->tss.eip = eip;
+	p->tss.eflags = eflags;
+	p->tss.eax = 0;
+	p->tss.ecx = ecx;
+	p->tss.edx = edx;
+	p->tss.ebx = ebx;
+	p->tss.esp = esp;
+	p->tss.ebp = ebp;
+	p->tss.esi = esi;
+	p->tss.edi = edi;
+	p->tss.es = es & 0xffff;
+	p->tss.cs = cs & 0xffff;
+	p->tss.ss = ss & 0xffff;
+	p->tss.ds = ds & 0xffff;
+	p->tss.fs = fs & 0xffff;
+	p->tss.gs = gs & 0xffff;
+	p->tss.ldt = _LDT(nr);
+	p->tss.trace_bitmap = 0x80000000;
+	if (last_task_used_math == current)
+		__asm__("fnsave %0"::"m" (p->tss.i387));
+	if (copy_mem(nr,p)) {
+		free_page((long) p);
+		return -EAGAIN;
+	}
+	for (i=0; i<NR_OPEN;i++)
+		if (f=p->filp[i])
+			f->f_count++;
+	if (current->pwd)
+		current->pwd->i_count++;
+	if (current->root)
+		current->root->i_count++;
+	set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY,&(p->tss));
+	set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY,&(p->ldt));
+	task[nr] = p;	/* do this last, just in case */
+	return last_pid;
+}
+
+int find_empty_process(void)
+{
+	int i;
+
+	repeat:
+		if ((++last_pid)<0) last_pid=1;
+		for(i=0 ; i<NR_TASKS ; i++)
+			if (task[i] && task[i]->pid == last_pid) goto repeat;
+	for(i=1 ; i<NR_TASKS ; i++)
+		if (!task[i])
+			return i;
+	return -EAGAIN;
+}