1 /* $NetBSD: kern_fork.c,v 1.30 1996/10/09 00:04:39 mycroft Exp $ */ 2 3 /* 4 * Copyright (c) 1982, 1986, 1989, 1991, 1993 5 * The Regents of the University of California. All rights reserved. 6 * (c) UNIX System Laboratories, Inc. 7 * All or some portions of this file are derived from material licensed 8 * to the University of California by American Telephone and Telegraph 9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 10 * the permission of UNIX System Laboratories, Inc. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. All advertising materials mentioning features or use of this software 21 * must display the following acknowledgement: 22 * This product includes software developed by the University of 23 * California, Berkeley and its contributors. 24 * 4. Neither the name of the University nor the names of its contributors 25 * may be used to endorse or promote products derived from this software 26 * without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 38 * SUCH DAMAGE. 39 * 40 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94 41 */ 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/map.h> 46 #include <sys/filedesc.h> 47 #include <sys/kernel.h> 48 #include <sys/malloc.h> 49 #include <sys/mount.h> 50 #include <sys/proc.h> 51 #include <sys/resourcevar.h> 52 #include <sys/vnode.h> 53 #include <sys/file.h> 54 #include <sys/acct.h> 55 #include <sys/ktrace.h> 56 57 #include <sys/syscallargs.h> 58 59 #include <vm/vm.h> 60 61 int nprocs = 1; /* process 0 */ 62 63 int fork1 __P((struct proc *, int, register_t *)); 64 65 /*ARGSUSED*/ 66 int 67 sys_fork(p, v, retval) 68 struct proc *p; 69 void *v; 70 register_t *retval; 71 { 72 73 return (fork1(p, 0, retval)); 74 } 75 76 /*ARGSUSED*/ 77 int 78 sys_vfork(p, v, retval) 79 struct proc *p; 80 void *v; 81 register_t *retval; 82 { 83 84 return (fork1(p, 1, retval)); 85 } 86 87 int 88 fork1(p1, isvfork, retval) 89 register struct proc *p1; 90 int isvfork; 91 register_t *retval; 92 { 93 register struct proc *p2; 94 register uid_t uid; 95 struct proc *newproc; 96 int count; 97 static int nextpid, pidchecked = 0; 98 99 /* 100 * Although process entries are dynamically created, we still keep 101 * a global limit on the maximum number we will create. Don't allow 102 * a nonprivileged user to use the last process; don't let root 103 * exceed the limit. The variable nprocs is the current number of 104 * processes, maxproc is the limit. 105 */ 106 uid = p1->p_cred->p_ruid; 107 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 108 tablefull("proc"); 109 return (EAGAIN); 110 } 111 112 /* 113 * Increment the count of procs running with this uid. Don't allow 114 * a nonprivileged user to exceed their current limit. 115 */ 116 count = chgproccnt(uid, 1); 117 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 118 (void)chgproccnt(uid, -1); 119 return (EAGAIN); 120 } 121 122 /* Allocate new proc. */ 123 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 124 125 /* 126 * Find an unused process ID. We remember a range of unused IDs 127 * ready to use (from nextpid+1 through pidchecked-1). 128 */ 129 nextpid++; 130 retry: 131 /* 132 * If the process ID prototype has wrapped around, 133 * restart somewhat above 0, as the low-numbered procs 134 * tend to include daemons that don't exit. 135 */ 136 if (nextpid >= PID_MAX) { 137 nextpid = 100; 138 pidchecked = 0; 139 } 140 if (nextpid >= pidchecked) { 141 int doingzomb = 0; 142 143 pidchecked = PID_MAX; 144 /* 145 * Scan the active and zombie procs to check whether this pid 146 * is in use. Remember the lowest pid that's greater 147 * than nextpid, so we can avoid checking for a while. 148 */ 149 p2 = allproc.lh_first; 150 again: 151 for (; p2 != 0; p2 = p2->p_list.le_next) { 152 while (p2->p_pid == nextpid || 153 p2->p_pgrp->pg_id == nextpid) { 154 nextpid++; 155 if (nextpid >= pidchecked) 156 goto retry; 157 } 158 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 159 pidchecked = p2->p_pid; 160 if (p2->p_pgrp->pg_id > nextpid && 161 pidchecked > p2->p_pgrp->pg_id) 162 pidchecked = p2->p_pgrp->pg_id; 163 } 164 if (!doingzomb) { 165 doingzomb = 1; 166 p2 = zombproc.lh_first; 167 goto again; 168 } 169 } 170 171 nprocs++; 172 p2 = newproc; 173 p2->p_stat = SIDL; /* protect against others */ 174 p2->p_pid = nextpid; 175 LIST_INSERT_HEAD(&allproc, p2, p_list); 176 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 177 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 178 179 /* 180 * Make a proc table entry for the new process. 181 * Start by zeroing the section of proc that is zero-initialized, 182 * then copy the section that is copied directly from the parent. 183 */ 184 bzero(&p2->p_startzero, 185 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 186 bcopy(&p1->p_startcopy, &p2->p_startcopy, 187 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 188 189 /* 190 * Duplicate sub-structures as needed. 191 * Increase reference counts on shared objects. 192 * The p_stats and p_sigacts substructs are set in vm_fork. 193 */ 194 p2->p_flag = P_INMEM; 195 p2->p_emul = p1->p_emul; 196 if (p1->p_flag & P_PROFIL) 197 startprofclock(p2); 198 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 199 M_SUBPROC, M_WAITOK); 200 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 201 p2->p_cred->p_refcnt = 1; 202 crhold(p1->p_ucred); 203 204 /* bump references to the text vnode (for procfs) */ 205 p2->p_textvp = p1->p_textvp; 206 if (p2->p_textvp) 207 VREF(p2->p_textvp); 208 209 p2->p_fd = fdcopy(p1); 210 /* 211 * If p_limit is still copy-on-write, bump refcnt, 212 * otherwise get a copy that won't be modified. 213 * (If PL_SHAREMOD is clear, the structure is shared 214 * copy-on-write.) 215 */ 216 if (p1->p_limit->p_lflags & PL_SHAREMOD) 217 p2->p_limit = limcopy(p1->p_limit); 218 else { 219 p2->p_limit = p1->p_limit; 220 p2->p_limit->p_refcnt++; 221 } 222 223 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 224 p2->p_flag |= P_CONTROLT; 225 if (isvfork) 226 p2->p_flag |= P_PPWAIT; 227 LIST_INSERT_AFTER(p1, p2, p_pglist); 228 p2->p_pptr = p1; 229 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 230 LIST_INIT(&p2->p_children); 231 232 #ifdef KTRACE 233 /* 234 * Copy traceflag and tracefile if enabled. 235 * If not inherited, these were zeroed above. 236 */ 237 if (p1->p_traceflag&KTRFAC_INHERIT) { 238 p2->p_traceflag = p1->p_traceflag; 239 if ((p2->p_tracep = p1->p_tracep) != NULL) 240 VREF(p2->p_tracep); 241 } 242 #endif 243 244 /* 245 * This begins the section where we must prevent the parent 246 * from being swapped. 247 */ 248 PHOLD(p1); 249 250 #ifdef __FORK_BRAINDAMAGE 251 /* 252 * Set return values for child before vm_fork, 253 * so they can be copied to child stack. 254 * We return 0, rather than the traditional behaviour of modifying the 255 * return value in the system call stub. 256 * NOTE: the kernel stack may be at a different location in the child 257 * process, and thus addresses of automatic variables (including retval) 258 * may be invalid after vm_fork returns in the child process. 259 */ 260 retval[0] = 0; 261 retval[1] = 1; 262 if (vm_fork(p1, p2)) 263 return (0); 264 #else 265 /* 266 * Finish creating the child process. It will return through a 267 * different path later. 268 */ 269 vm_fork(p1, p2); 270 #endif 271 272 /* 273 * Make child runnable, set start time, and add to run queue. 274 */ 275 (void) splstatclock(); 276 p2->p_stats->p_start = time; 277 p2->p_acflag = AFORK; 278 p2->p_stat = SRUN; 279 setrunqueue(p2); 280 (void) spl0(); 281 282 /* 283 * Now can be swapped. 284 */ 285 PRELE(p1); 286 287 /* 288 * Preserve synchronization semantics of vfork. If waiting for 289 * child to exec or exit, set P_PPWAIT on child, and sleep on our 290 * proc (in case of exit). 291 */ 292 if (isvfork) 293 while (p2->p_flag & P_PPWAIT) 294 tsleep(p1, PWAIT, "ppwait", 0); 295 296 /* 297 * Return child pid to parent process, 298 * marking us as parent via retval[1]. 299 */ 300 retval[0] = p2->p_pid; 301 retval[1] = 0; 302 return (0); 303 } 304