kernel/fork.c

/* */
This source file includes following definitions.
find_empty_process
get_pid
dup_mmap
copy_mm
copy_fs
copy_files
copy_sighand
do_fork
   1 /*
   2  *  linux/kernel/fork.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  */
   6 
   7 /*
   8  *  'fork.c' contains the help-routines for the 'fork' system call
   9  * (see also system_call.s).
  10  * Fork is rather simple, once you get the hang of it, but the memory
  11  * management can be a bitch. See 'mm/mm.c': 'copy_page_tables()'
  12  */
  13 
  14 #include <linux/errno.h>
  15 #include <linux/sched.h>
  16 #include <linux/kernel.h>
  17 #include <linux/mm.h>
  18 #include <linux/stddef.h>
  19 #include <linux/unistd.h>
  20 #include <linux/ptrace.h>
  21 #include <linux/malloc.h>
  22 #include <linux/ldt.h>
  23 #include <linux/smp.h>
  24 
  25 #include <asm/segment.h>
  26 #include <asm/system.h>
  27 #include <asm/pgtable.h>
  28 
  29 int nr_tasks=1;
  30 int nr_running=1;
  31 
  32 static inline int find_empty_process(void)
     /*  */
  33 {
  34         int i;
  35         struct task_struct *p;
  36 
  37         if (nr_tasks >= NR_TASKS - MIN_TASKS_LEFT_FOR_ROOT) {
  38                 if (current->uid)
  39                         return -EAGAIN;
  40         }
  41         if (current->uid) {
  42                 long max_tasks = current->rlim[RLIMIT_NPROC].rlim_cur;
  43 
  44                 if (max_tasks < nr_tasks) {
  45                         for_each_task (p) {
  46                                 if (p->uid == current->uid)
  47                                         if (--max_tasks < 0)
  48                                                 return -EAGAIN;
  49                         }
  50                 }
  51         }
  52         for (i = 0 ; i < NR_TASKS ; i++) {
  53                 if (!task[i])
  54                         return i;
  55         }
  56         return -EAGAIN;
  57 }
  58 
  59 static int get_pid(unsigned long flags)
     /*  */
  60 {
  61         static int last_pid = 0;
  62         struct task_struct *p;
  63 
  64         if (flags & CLONE_PID)
  65                 return current->pid;
  66 repeat:
  67         if ((++last_pid) & 0xffff8000)
  68                 last_pid=1;
  69         for_each_task (p) {
  70                 if (p->pid == last_pid ||
  71                     p->pgrp == last_pid ||
  72                     p->session == last_pid)
  73                         goto repeat;
  74         }
  75         return last_pid;
  76 }
  77 
  78 static inline int dup_mmap(struct mm_struct * mm)
     /*  */
  79 {
  80         struct vm_area_struct * mpnt, **p, *tmp;
  81 
  82         mm->mmap = NULL;
  83         p = &mm->mmap;
  84         for (mpnt = current->mm->mmap ; mpnt ; mpnt = mpnt->vm_next) {
  85                 tmp = (struct vm_area_struct *) kmalloc(sizeof(struct vm_area_struct), GFP_KERNEL);
  86                 if (!tmp) {
  87                         exit_mmap(mm);
  88                         return -ENOMEM;
  89                 }
  90                 *tmp = *mpnt;
  91                 tmp->vm_flags &= ~VM_LOCKED;
  92                 tmp->vm_mm = mm;
  93                 tmp->vm_next = NULL;
  94                 if (tmp->vm_inode) {
  95                         tmp->vm_inode->i_count++;
  96                         /* insert tmp into the share list, just after mpnt */
  97                         tmp->vm_next_share->vm_prev_share = tmp;
  98                         mpnt->vm_next_share = tmp;
  99                         tmp->vm_prev_share = mpnt;
 100                 }
 101                 if (tmp->vm_ops && tmp->vm_ops->open)
 102                         tmp->vm_ops->open(tmp);
 103                 if (copy_page_range(mm, current->mm, tmp)) {
 104                         exit_mmap(mm);
 105                         return -ENOMEM;
 106                 }
 107                 *p = tmp;
 108                 p = &tmp->vm_next;
 109         }
 110         build_mmap_avl(mm);
 111         return 0;
 112 }
 113 
 114 static inline int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 115 {
 116         if (clone_flags & CLONE_VM) {
 117                 SET_PAGE_DIR(tsk, current->mm->pgd);
 118                 current->mm->count++;
 119                 return 0;
 120         }
 121         tsk->mm = kmalloc(sizeof(*tsk->mm), GFP_KERNEL);
 122         if (!tsk->mm)
 123                 return -1;
 124         *tsk->mm = *current->mm;
 125         tsk->mm->count = 1;
 126         tsk->mm->def_flags = 0;
 127         tsk->min_flt = tsk->maj_flt = 0;
 128         tsk->cmin_flt = tsk->cmaj_flt = 0;
 129         tsk->nswap = tsk->cnswap = 0;
 130         if (new_page_tables(tsk))
 131                 return -1;
 132         if (dup_mmap(tsk->mm)) {
 133                 free_page_tables(tsk);
 134                 return -1;
 135         }
 136         return 0;
 137 }
 138 
 139 static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 140 {
 141         if (clone_flags & CLONE_FS) {
 142                 current->fs->count++;
 143                 return 0;
 144         }
 145         tsk->fs = kmalloc(sizeof(*tsk->fs), GFP_KERNEL);
 146         if (!tsk->fs)
 147                 return -1;
 148         tsk->fs->count = 1;
 149         tsk->fs->umask = current->fs->umask;
 150         if ((tsk->fs->root = current->fs->root))
 151                 tsk->fs->root->i_count++;
 152         if ((tsk->fs->pwd = current->fs->pwd))
 153                 tsk->fs->pwd->i_count++;
 154         return 0;
 155 }
 156 
 157 static inline int copy_files(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 158 {
 159         int i;
 160 
 161         if (clone_flags & CLONE_FILES) {
 162                 current->files->count++;
 163                 return 0;
 164         }
 165         tsk->files = kmalloc(sizeof(*tsk->files), GFP_KERNEL);
 166         if (!tsk->files)
 167                 return -1;
 168         tsk->files->count = 1;
 169         memcpy(&tsk->files->close_on_exec, &current->files->close_on_exec,
 170                 sizeof(tsk->files->close_on_exec));
 171         for (i = 0; i < NR_OPEN; i++) {
 172                 struct file * f = current->files->fd[i];
 173                 if (f)
 174                         f->f_count++;
 175                 tsk->files->fd[i] = f;
 176         }
 177         return 0;
 178 }
 179 
 180 static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 181 {
 182         if (clone_flags & CLONE_SIGHAND) {
 183                 current->sig->count++;
 184                 return 0;
 185         }
 186         tsk->sig = kmalloc(sizeof(*tsk->sig), GFP_KERNEL);
 187         if (!tsk->sig)
 188                 return -1;
 189         tsk->sig->count = 1;
 190         memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
 191         return 0;
 192 }
 193 
 194 /*
 195  *  Ok, this is the main fork-routine. It copies the system process
 196  * information (task[nr]) and sets up the necessary registers. It
 197  * also copies the data segment in its entirety.
 198  */
 199 int do_fork(unsigned long clone_flags, unsigned long usp, struct pt_regs *regs)
     /*  */
 200 {
 201         int nr;
 202         int error = -ENOMEM;
 203         unsigned long new_stack;
 204         struct task_struct *p;
 205 
 206         p = (struct task_struct *) kmalloc(sizeof(*p), GFP_KERNEL);
 207         if (!p)
 208                 goto bad_fork;
 209         new_stack = alloc_kernel_stack();
 210         if (!new_stack)
 211                 goto bad_fork_free_p;
 212         error = -EAGAIN;
 213         nr = find_empty_process();
 214         if (nr < 0)
 215                 goto bad_fork_free_stack;
 216 
 217         *p = *current;
 218 
 219         if (p->exec_domain && p->exec_domain->use_count)
 220                 (*p->exec_domain->use_count)++;
 221         if (p->binfmt && p->binfmt->use_count)
 222                 (*p->binfmt->use_count)++;
 223 
 224         p->did_exec = 0;
 225         p->swappable = 0;
 226         p->kernel_stack_page = new_stack;
 227         *(unsigned long *) p->kernel_stack_page = STACK_MAGIC;
 228         p->state = TASK_UNINTERRUPTIBLE;
 229         p->flags &= ~(PF_PTRACED|PF_TRACESYS);
 230         p->pid = get_pid(clone_flags);
 231         p->next_run = NULL;
 232         p->prev_run = NULL;
 233         p->p_pptr = p->p_opptr = current;
 234         p->p_cptr = NULL;
 235         p->signal = 0;
 236         p->it_real_value = p->it_virt_value = p->it_prof_value = 0;
 237         p->it_real_incr = p->it_virt_incr = p->it_prof_incr = 0;
 238         init_timer(&p->real_timer);
 239         p->real_timer.data = (unsigned long) p;
 240         p->leader = 0;          /* process leadership doesn't inherit */
 241         p->tty_old_pgrp = 0;
 242         p->utime = p->stime = 0;
 243         p->cutime = p->cstime = 0;
 244 #ifdef __SMP__
 245         p->processor = NO_PROC_ID;
 246         p->lock_depth = 1;
 247 #endif
 248         p->start_time = jiffies;
 249         task[nr] = p;
 250         SET_LINKS(p);
 251         nr_tasks++;
 252 
 253         error = -ENOMEM;
 254         /* copy all the process information */
 255         if (copy_files(clone_flags, p))
 256                 goto bad_fork_cleanup;
 257         if (copy_fs(clone_flags, p))
 258                 goto bad_fork_cleanup_files;
 259         if (copy_sighand(clone_flags, p))
 260                 goto bad_fork_cleanup_fs;
 261         if (copy_mm(clone_flags, p))
 262                 goto bad_fork_cleanup_sighand;
 263         copy_thread(nr, clone_flags, usp, p, regs);
 264         p->semundo = NULL;
 265 
 266         /* ok, now we should be set up.. */
 267         p->swappable = 1;
 268         p->exit_signal = clone_flags & CSIGNAL;
 269         p->counter = current->counter >> 1;
 270         wake_up_process(p);                     /* do this last, just in case */
 271         return p->pid;
 272 
 273 bad_fork_cleanup_sighand:
 274         exit_sighand(p);
 275 bad_fork_cleanup_fs:
 276         exit_fs(p);
 277 bad_fork_cleanup_files:
 278         exit_files(p);
 279 bad_fork_cleanup:
 280         if (p->exec_domain && p->exec_domain->use_count)
 281                 (*p->exec_domain->use_count)--;
 282         if (p->binfmt && p->binfmt->use_count)
 283                 (*p->binfmt->use_count)--;
 284         task[nr] = NULL;
 285         REMOVE_LINKS(p);
 286         nr_tasks--;
 287 bad_fork_free_stack:
 288         free_kernel_stack(new_stack);
 289 bad_fork_free_p:
 290         kfree(p);
 291 bad_fork:
 292         return error;
 293 }
/* */
root/kernel/fork.c

DEFINITIONS
