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 unsigned long int total_forks=0;        /* Handle normal Linux uptimes. */
  32 
  33 static inline int find_empty_process(void)
     /*  */
  34 {
  35         int i;
  36         struct task_struct *p;
  37 
  38         if (nr_tasks >= NR_TASKS - MIN_TASKS_LEFT_FOR_ROOT) {
  39                 if (current->uid)
  40                         return -EAGAIN;
  41         }
  42         if (current->uid) {
  43                 long max_tasks = current->rlim[RLIMIT_NPROC].rlim_cur;
  44 
  45                 if (max_tasks < nr_tasks) {
  46                         for_each_task (p) {
  47                                 if (p->uid == current->uid)
  48                                         if (--max_tasks < 0)
  49                                                 return -EAGAIN;
  50                         }
  51                 }
  52         }
  53         for (i = 0 ; i < NR_TASKS ; i++) {
  54                 if (!task[i])
  55                         return i;
  56         }
  57         return -EAGAIN;
  58 }
  59 
  60 static int get_pid(unsigned long flags)
     /*  */
  61 {
  62         static int last_pid = 0;
  63         struct task_struct *p;
  64 
  65         if (flags & CLONE_PID)
  66                 return current->pid;
  67 repeat:
  68         if ((++last_pid) & 0xffff8000)
  69                 last_pid=1;
  70         for_each_task (p) {
  71                 if (p->pid == last_pid ||
  72                     p->pgrp == last_pid ||
  73                     p->session == last_pid)
  74                         goto repeat;
  75         }
  76         return last_pid;
  77 }
  78 
  79 static inline int dup_mmap(struct mm_struct * mm)
     /*  */
  80 {
  81         struct vm_area_struct * mpnt, **p, *tmp;
  82 
  83         mm->mmap = NULL;
  84         p = &mm->mmap;
  85         for (mpnt = current->mm->mmap ; mpnt ; mpnt = mpnt->vm_next) {
  86                 tmp = (struct vm_area_struct *) kmalloc(sizeof(struct vm_area_struct), GFP_KERNEL);
  87                 if (!tmp) {
  88                         exit_mmap(mm);
  89                         return -ENOMEM;
  90                 }
  91                 *tmp = *mpnt;
  92                 tmp->vm_flags &= ~VM_LOCKED;
  93                 tmp->vm_mm = mm;
  94                 tmp->vm_next = NULL;
  95                 if (tmp->vm_inode) {
  96                         tmp->vm_inode->i_count++;
  97                         /* insert tmp into the share list, just after mpnt */
  98                         tmp->vm_next_share->vm_prev_share = tmp;
  99                         mpnt->vm_next_share = tmp;
 100                         tmp->vm_prev_share = mpnt;
 101                 }
 102                 if (tmp->vm_ops && tmp->vm_ops->open)
 103                         tmp->vm_ops->open(tmp);
 104                 if (copy_page_range(mm, current->mm, tmp)) {
 105                         exit_mmap(mm);
 106                         return -ENOMEM;
 107                 }
 108                 *p = tmp;
 109                 p = &tmp->vm_next;
 110         }
 111         build_mmap_avl(mm);
 112         return 0;
 113 }
 114 
 115 static inline int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 116 {
 117         if (clone_flags & CLONE_VM) {
 118                 SET_PAGE_DIR(tsk, current->mm->pgd);
 119                 current->mm->count++;
 120                 return 0;
 121         }
 122         tsk->mm = kmalloc(sizeof(*tsk->mm), GFP_KERNEL);
 123         if (!tsk->mm)
 124                 return -1;
 125         *tsk->mm = *current->mm;
 126         tsk->mm->count = 1;
 127         tsk->mm->def_flags = 0;
 128         tsk->min_flt = tsk->maj_flt = 0;
 129         tsk->cmin_flt = tsk->cmaj_flt = 0;
 130         tsk->nswap = tsk->cnswap = 0;
 131         if (new_page_tables(tsk))
 132                 return -1;
 133         if (dup_mmap(tsk->mm)) {
 134                 free_page_tables(tsk);
 135                 return -1;
 136         }
 137         return 0;
 138 }
 139 
 140 static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 141 {
 142         if (clone_flags & CLONE_FS) {
 143                 current->fs->count++;
 144                 return 0;
 145         }
 146         tsk->fs = kmalloc(sizeof(*tsk->fs), GFP_KERNEL);
 147         if (!tsk->fs)
 148                 return -1;
 149         tsk->fs->count = 1;
 150         tsk->fs->umask = current->fs->umask;
 151         if ((tsk->fs->root = current->fs->root))
 152                 tsk->fs->root->i_count++;
 153         if ((tsk->fs->pwd = current->fs->pwd))
 154                 tsk->fs->pwd->i_count++;
 155         return 0;
 156 }
 157 
 158 static inline int copy_files(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 159 {
 160         int i;
 161 
 162         if (clone_flags & CLONE_FILES) {
 163                 current->files->count++;
 164                 return 0;
 165         }
 166         tsk->files = kmalloc(sizeof(*tsk->files), GFP_KERNEL);
 167         if (!tsk->files)
 168                 return -1;
 169         tsk->files->count = 1;
 170         memcpy(&tsk->files->close_on_exec, &current->files->close_on_exec,
 171                 sizeof(tsk->files->close_on_exec));
 172         for (i = 0; i < NR_OPEN; i++) {
 173                 struct file * f = current->files->fd[i];
 174                 if (f)
 175                         f->f_count++;
 176                 tsk->files->fd[i] = f;
 177         }
 178         return 0;
 179 }
 180 
 181 static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
     /*  */
 182 {
 183         if (clone_flags & CLONE_SIGHAND) {
 184                 current->sig->count++;
 185                 return 0;
 186         }
 187         tsk->sig = kmalloc(sizeof(*tsk->sig), GFP_KERNEL);
 188         if (!tsk->sig)
 189                 return -1;
 190         tsk->sig->count = 1;
 191         memcpy(tsk->sig->action, current->sig->action, sizeof(tsk->sig->action));
 192         return 0;
 193 }
 194 
 195 /*
 196  *  Ok, this is the main fork-routine. It copies the system process
 197  * information (task[nr]) and sets up the necessary registers. It
 198  * also copies the data segment in its entirety.
 199  */
 200 int do_fork(unsigned long clone_flags, unsigned long usp, struct pt_regs *regs)
     /*  */
 201 {
 202         int nr;
 203         int error = -ENOMEM;
 204         unsigned long new_stack;
 205         struct task_struct *p;
 206 
 207         p = (struct task_struct *) kmalloc(sizeof(*p), GFP_KERNEL);
 208         if (!p)
 209                 goto bad_fork;
 210         new_stack = alloc_kernel_stack();
 211         if (!new_stack)
 212                 goto bad_fork_free_p;
 213         error = -EAGAIN;
 214         nr = find_empty_process();
 215         if (nr < 0)
 216                 goto bad_fork_free_stack;
 217 
 218         *p = *current;
 219 
 220         if (p->exec_domain && p->exec_domain->use_count)
 221                 (*p->exec_domain->use_count)++;
 222         if (p->binfmt && p->binfmt->use_count)
 223                 (*p->binfmt->use_count)++;
 224 
 225         p->did_exec = 0;
 226         p->swappable = 0;
 227         p->kernel_stack_page = new_stack;
 228         *(unsigned long *) p->kernel_stack_page = STACK_MAGIC;
 229         p->state = TASK_UNINTERRUPTIBLE;
 230         p->flags &= ~(PF_PTRACED|PF_TRACESYS|PF_SUPERPREV);
 231         p->flags |= PF_FORKNOEXEC;
 232         p->pid = get_pid(clone_flags);
 233         p->next_run = NULL;
 234         p->prev_run = NULL;
 235         p->p_pptr = p->p_opptr = current;
 236         p->p_cptr = NULL;
 237         p->signal = 0;
 238         p->it_real_value = p->it_virt_value = p->it_prof_value = 0;
 239         p->it_real_incr = p->it_virt_incr = p->it_prof_incr = 0;
 240         init_timer(&p->real_timer);
 241         p->real_timer.data = (unsigned long) p;
 242         p->leader = 0;          /* process leadership doesn't inherit */
 243         p->tty_old_pgrp = 0;
 244         p->utime = p->stime = 0;
 245         p->cutime = p->cstime = 0;
 246 #ifdef __SMP__
 247         p->processor = NO_PROC_ID;
 248         p->lock_depth = 1;
 249 #endif
 250         p->start_time = jiffies;
 251         task[nr] = p;
 252         SET_LINKS(p);
 253         nr_tasks++;
 254 
 255         error = -ENOMEM;
 256         /* copy all the process information */
 257         if (copy_files(clone_flags, p))
 258                 goto bad_fork_cleanup;
 259         if (copy_fs(clone_flags, p))
 260                 goto bad_fork_cleanup_files;
 261         if (copy_sighand(clone_flags, p))
 262                 goto bad_fork_cleanup_fs;
 263         if (copy_mm(clone_flags, p))
 264                 goto bad_fork_cleanup_sighand;
 265         copy_thread(nr, clone_flags, usp, p, regs);
 266         p->semundo = NULL;
 267 
 268         /* ok, now we should be set up.. */
 269         p->swappable = 1;
 270         p->exit_signal = clone_flags & CSIGNAL;
 271         p->counter = current->counter >> 1;
 272         wake_up_process(p);                     /* do this last, just in case */
 273         ++total_forks;
 274         return p->pid;
 275 
 276 bad_fork_cleanup_sighand:
 277         exit_sighand(p);
 278 bad_fork_cleanup_fs:
 279         exit_fs(p);
 280 bad_fork_cleanup_files:
 281         exit_files(p);
 282 bad_fork_cleanup:
 283         if (p->exec_domain && p->exec_domain->use_count)
 284                 (*p->exec_domain->use_count)--;
 285         if (p->binfmt && p->binfmt->use_count)
 286                 (*p->binfmt->use_count)--;
 287         task[nr] = NULL;
 288         REMOVE_LINKS(p);
 289         nr_tasks--;
 290 bad_fork_free_stack:
 291         free_kernel_stack(new_stack);
 292 bad_fork_free_p:
 293         kfree(p);
 294 bad_fork:
 295         return error;
 296 }
/* */
root/kernel/fork.c

DEFINITIONS
