kernel/fork.c



/*
* linux/kernel/fork.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/

/*
* 'fork.c' contains the help-routines for the 'fork' system call
* (see also system_call.s).
* 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 <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/ptrace.h>
#include <linux/malloc.h>
#include <linux/ldt.h>
#include <linux/smp.h>

#include <asm/segment.h>
#include <asm/system.h>
#include <asm/pgtable.h>

int nr_tasks=1;
int nr_running=1;
unsigned long int total_forks=0; /* Handle normal Linux uptimes. */
int last_pid=0;




static inline int find_empty_process(void)
{
int i;
struct task_struct *p;

if (nr_tasks >= NR_TASKS - MIN_TASKS_LEFT_FOR_ROOT) {
if (current->uid)
return -EAGAIN;
}
if (current->uid) {
long max_tasks = current->rlim[RLIMIT_NPROC].rlim_cur;

if (max_tasks < nr_tasks) {
for_each_task (p) {
if (p->uid == current->uid)
if (--max_tasks < 0)
return -EAGAIN;
}
}
}
for (i = 0 ; i < NR_TASKS ; i++) {
if (!task[i])
return i;
}
return -EAGAIN;
}




static int get_pid(unsigned long flags)
{
struct task_struct *p;

if (flags & CLONE_PID)
return current->pid;
repeat:
if ((++last_pid) & 0xffff8000)
last_pid=1;
for_each_task (p) {
if (p->pid == last_pid ||
p->pgrp == last_pid ||
p->session == last_pid)
goto repeat;
}
return last_pid;
}




static inline int dup_mmap(struct mm_struct * mm)
{
struct vm_area_struct * mpnt, **p, *tmp;

mm->mmap = NULL;
p = &mm->mmap;
for (mpnt = current->mm->mmap ; mpnt ; mpnt = mpnt->vm_next) {
tmp = (struct vm_area_struct *) kmalloc(sizeof(struct vm_area_struct), GFP_KERNEL);
if (!tmp) {
exit_mmap(mm);
return -ENOMEM;
}
*tmp = *mpnt;
tmp->vm_flags &= ~VM_LOCKED;
tmp->vm_mm = mm;
tmp->vm_next = NULL;
if (tmp->vm_inode) {
tmp->vm_inode->i_count++;
/* insert tmp into the share list, just after mpnt */
tmp->vm_next_share->vm_prev_share = tmp;
mpnt->vm_next_share = tmp;
tmp->vm_prev_share = mpnt;
}
if (tmp->vm_ops && tmp->vm_ops->open)
tmp->vm_ops->open(tmp);
if (copy_page_range(mm, current->mm, tmp)) {
exit_mmap(mm);
return -ENOMEM;
}
*p = tmp;
p = &tmp->vm_next;
}
build_mmap_avl(mm);
return 0;
}




static inline int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
{
if (!(clone_flags & CLONE_VM)) {
struct mm_struct * mm = kmalloc(sizeof(*tsk->mm), GFP_KERNEL);
if (!mm)
return -1;
*mm = *current->mm;
mm->count = 1;
mm->def_flags = 0;
tsk->mm = mm;
tsk->min_flt = tsk->maj_flt = 0;
tsk->cmin_flt = tsk->cmaj_flt = 0;
tsk->nswap = tsk->cnswap = 0;
if (new_page_tables(tsk))
return -1;
if (dup_mmap(mm)) {
free_page_tables(mm);
return -1;
}
return 0;
}
SET_PAGE_DIR(tsk, current->mm->pgd);
current->mm->count++;
return 0;
}




static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
{
if (clone_flags & CLONE_FS) {
current->fs->count++;
return 0;
}
tsk->fs = kmalloc(sizeof(*tsk->fs), GFP_KERNEL);
if (!tsk->fs)
return -1;
tsk->fs->count = 1;
tsk->fs->umask = current->fs->umask;
if ((tsk->fs->root = current->fs->root))
tsk->fs->root->i_count++;
if ((tsk->fs->pwd = current->fs->pwd))
tsk->fs->pwd->i_count++;
return 0;
}




static inline int copy_files(unsigned long clone_flags, struct task_struct * tsk)
{
int i;

if (clone_flags & CLONE_FILES) {
current->files->count++;
return 0;
}
tsk->files = kmalloc(sizeof(*tsk->files), GFP_KERNEL);
if (!tsk->files)
return -1;
tsk->files->count = 1;
memcpy(&tsk->files->close_on_exec, ¤t->files->close_on_exec,
sizeof(tsk->files->close_on_exec));
for (i = 0; i < NR_OPEN; i++) {
struct file * f = current->files->fd[i];
if (f)
f->f_count++;
tsk->files->fd[i] = f;
}
return 0;
}




static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
{
if (clone_flags & CLONE_SIGHAND) {
current->sig->count++;
return 0;
}
tsk->sig = kmalloc(sizeof(*tsk->sig), GFP_KERNEL);
if (!tsk->sig)
return -1;
tsk->sig->count = 1;
memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
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 its entirety.
*/
int do_fork(unsigned long clone_flags, unsigned long usp, struct pt_regs *regs)
{
int nr;
int error = -ENOMEM;
unsigned long new_stack;
struct task_struct *p;

p = (struct task_struct *) kmalloc(sizeof(*p), GFP_KERNEL);
if (!p)
goto bad_fork;
new_stack = alloc_kernel_stack();
if (!new_stack)
goto bad_fork_free_p;
error = -EAGAIN;
nr = find_empty_process();
if (nr < 0)
goto bad_fork_free_stack;

*p = *current;

if (p->exec_domain && p->exec_domain->use_count)
(*p->exec_domain->use_count)++;
if (p->binfmt && p->binfmt->use_count)
(*p->binfmt->use_count)++;

p->did_exec = 0;
p->swappable = 0;
p->kernel_stack_page = new_stack;
*(unsigned long *) p->kernel_stack_page = STACK_MAGIC;
p->state = TASK_UNINTERRUPTIBLE;
p->flags &= ~(PF_PTRACED|PF_TRACESYS|PF_SUPERPRIV);
p->flags |= PF_FORKNOEXEC;
p->pid = get_pid(clone_flags);
p->next_run = NULL;
p->prev_run = NULL;
p->p_pptr = p->p_opptr = current;
p->p_cptr = NULL;
p->signal = 0;
p->it_real_value = p->it_virt_value = p->it_prof_value = 0;
p->it_real_incr = p->it_virt_incr = p->it_prof_incr = 0;
init_timer(&p->real_timer);
p->real_timer.data = (unsigned long) p;
p->leader = 0; /* process leadership doesn't inherit */
p->tty_old_pgrp = 0;
p->utime = p->stime = 0;
p->cutime = p->cstime = 0;
#ifdef __SMP__
p->processor = NO_PROC_ID;
p->lock_depth = 1;
#endif
p->start_time = jiffies;
task[nr] = p;
SET_LINKS(p);
nr_tasks++;

error = -ENOMEM;
/* copy all the process information */
if (copy_files(clone_flags, p))
goto bad_fork_cleanup;
if (copy_fs(clone_flags, p))
goto bad_fork_cleanup_files;
if (copy_sighand(clone_flags, p))
goto bad_fork_cleanup_fs;
if (copy_mm(clone_flags, p))
goto bad_fork_cleanup_sighand;
copy_thread(nr, clone_flags, usp, p, regs);
p->semundo = NULL;

/* ok, now we should be set up.. */
p->swappable = 1;
p->exit_signal = clone_flags & CSIGNAL;
p->counter = current->counter >> 1;
wake_up_process(p); /* do this last, just in case */
++total_forks;
return p->pid;

bad_fork_cleanup_sighand:
exit_sighand(p);
bad_fork_cleanup_fs:
exit_fs(p);
bad_fork_cleanup_files:
exit_files(p);
bad_fork_cleanup:
if (p->exec_domain && p->exec_domain->use_count)
(*p->exec_domain->use_count)--;
if (p->binfmt && p->binfmt->use_count)
(*p->binfmt->use_count)--;
task[nr] = NULL;
REMOVE_LINKS(p);
nr_tasks--;
bad_fork_free_stack:
free_kernel_stack(new_stack);
bad_fork_free_p:
kfree(p);
bad_fork:
return error;
}