1 /* 2 * Copyright (c) 1982, 1986, 1989, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * (c) UNIX System Laboratories, Inc. 5 * All or some portions of this file are derived from material licensed 6 * to the University of California by American Telephone and Telegraph 7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8 * the permission of UNIX System Laboratories, Inc. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_fork.c 8.6 (Berkeley) 4/8/94 39 * $Id: kern_fork.c,v 1.4 1994/08/06 07:15:04 davidg Exp $ 40 */ 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/map.h> 45 #include <sys/filedesc.h> 46 #include <sys/kernel.h> 47 #include <sys/malloc.h> 48 #include <sys/proc.h> 49 #include <sys/resourcevar.h> 50 #include <sys/vnode.h> 51 #include <sys/file.h> 52 #include <sys/acct.h> 53 #include <sys/ktrace.h> 54 55 static int fork1(struct proc *, int, int *); 56 57 struct fork_args { 58 int dummy; 59 }; 60 /* ARGSUSED */ 61 int 62 fork(p, uap, retval) 63 struct proc *p; 64 struct fork_args *uap; 65 int retval[]; 66 { 67 68 return (fork1(p, 0, retval)); 69 } 70 71 /* ARGSUSED */ 72 int 73 vfork(p, uap, retval) 74 struct proc *p; 75 struct fork_args *uap; 76 int retval[]; 77 { 78 79 return (fork1(p, 1, retval)); 80 } 81 82 int nprocs = 1; /* process 0 */ 83 84 static int 85 fork1(p1, isvfork, retval) 86 register struct proc *p1; 87 int isvfork, retval[]; 88 { 89 register struct proc *p2; 90 register uid_t uid; 91 struct proc *newproc; 92 struct proc **hash; 93 int count; 94 static int nextpid, pidchecked = 0; 95 96 /* 97 * Although process entries are dynamically created, we still keep 98 * a global limit on the maximum number we will create. Don't allow 99 * a nonprivileged user to use the last process; don't let root 100 * exceed the limit. The variable nprocs is the current number of 101 * processes, maxproc is the limit. 102 */ 103 uid = p1->p_cred->p_ruid; 104 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 105 tablefull("proc"); 106 return (EAGAIN); 107 } 108 /* 109 * Increment the count of procs running with this uid. Don't allow 110 * a nonprivileged user to exceed their current limit. 111 */ 112 count = chgproccnt(uid, 1); 113 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 114 (void)chgproccnt(uid, -1); 115 return (EAGAIN); 116 } 117 118 /* Allocate new proc. */ 119 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 120 121 /* 122 * Find an unused process ID. We remember a range of unused IDs 123 * ready to use (from nextpid+1 through pidchecked-1). 124 */ 125 nextpid++; 126 retry: 127 /* 128 * If the process ID prototype has wrapped around, 129 * restart somewhat above 0, as the low-numbered procs 130 * tend to include daemons that don't exit. 131 */ 132 if (nextpid >= PID_MAX) { 133 nextpid = 100; 134 pidchecked = 0; 135 } 136 if (nextpid >= pidchecked) { 137 int doingzomb = 0; 138 139 pidchecked = PID_MAX; 140 /* 141 * Scan the active and zombie procs to check whether this pid 142 * is in use. Remember the lowest pid that's greater 143 * than nextpid, so we can avoid checking for a while. 144 */ 145 p2 = (struct proc *)allproc; 146 again: 147 for (; p2 != NULL; p2 = p2->p_next) { 148 while (p2->p_pid == nextpid || 149 p2->p_pgrp->pg_id == nextpid) { 150 nextpid++; 151 if (nextpid >= pidchecked) 152 goto retry; 153 } 154 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 155 pidchecked = p2->p_pid; 156 if (p2->p_pgrp->pg_id > nextpid && 157 pidchecked > p2->p_pgrp->pg_id) 158 pidchecked = p2->p_pgrp->pg_id; 159 } 160 if (!doingzomb) { 161 doingzomb = 1; 162 p2 = zombproc; 163 goto again; 164 } 165 } 166 167 168 /* 169 * Link onto allproc (this should probably be delayed). 170 * Heavy use of volatile here to prevent the compiler from 171 * rearranging code. Yes, it *is* terribly ugly, but at least 172 * it works. 173 */ 174 nprocs++; 175 p2 = newproc; 176 #define Vp2 ((volatile struct proc *)p2) 177 Vp2->p_stat = SIDL; /* protect against others */ 178 Vp2->p_pid = nextpid; 179 /* 180 * This is really: 181 * p2->p_next = allproc; 182 * allproc->p_prev = &p2->p_next; 183 * p2->p_prev = &allproc; 184 * allproc = p2; 185 * The assignment via allproc is legal since it is never NULL. 186 */ 187 *(volatile struct proc **)&Vp2->p_next = allproc; 188 *(volatile struct proc ***)&allproc->p_prev = 189 (volatile struct proc **)&Vp2->p_next; 190 *(volatile struct proc ***)&Vp2->p_prev = &allproc; 191 allproc = Vp2; 192 #undef Vp2 193 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 194 195 /* Insert on the hash chain. */ 196 hash = &pidhash[PIDHASH(p2->p_pid)]; 197 p2->p_hash = *hash; 198 *hash = p2; 199 200 /* 201 * Make a proc table entry for the new process. 202 * Start by zeroing the section of proc that is zero-initialized, 203 * then copy the section that is copied directly from the parent. 204 */ 205 bzero(&p2->p_startzero, 206 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 207 bcopy(&p1->p_startcopy, &p2->p_startcopy, 208 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 209 210 /* 211 * Duplicate sub-structures as needed. 212 * Increase reference counts on shared objects. 213 * The p_stats and p_sigacts substructs are set in vm_fork. 214 */ 215 p2->p_flag = P_INMEM; 216 if (p1->p_flag & P_PROFIL) 217 startprofclock(p2); 218 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 219 M_SUBPROC, M_WAITOK); 220 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 221 p2->p_cred->p_refcnt = 1; 222 crhold(p1->p_ucred); 223 224 /* bump references to the text vnode (for procfs) */ 225 p2->p_textvp = p1->p_textvp; 226 if (p2->p_textvp) 227 VREF(p2->p_textvp); 228 229 p2->p_fd = fdcopy(p1); 230 /* 231 * If p_limit is still copy-on-write, bump refcnt, 232 * otherwise get a copy that won't be modified. 233 * (If PL_SHAREMOD is clear, the structure is shared 234 * copy-on-write.) 235 */ 236 if (p1->p_limit->p_lflags & PL_SHAREMOD) 237 p2->p_limit = limcopy(p1->p_limit); 238 else { 239 p2->p_limit = p1->p_limit; 240 p2->p_limit->p_refcnt++; 241 } 242 243 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 244 p2->p_flag |= P_CONTROLT; 245 if (isvfork) 246 p2->p_flag |= P_PPWAIT; 247 p2->p_pgrpnxt = p1->p_pgrpnxt; 248 p1->p_pgrpnxt = p2; 249 p2->p_pptr = p1; 250 p2->p_osptr = p1->p_cptr; 251 if (p1->p_cptr) 252 p1->p_cptr->p_ysptr = p2; 253 p1->p_cptr = p2; 254 #ifdef KTRACE 255 /* 256 * Copy traceflag and tracefile if enabled. 257 * If not inherited, these were zeroed above. 258 */ 259 if (p1->p_traceflag&KTRFAC_INHERIT) { 260 p2->p_traceflag = p1->p_traceflag; 261 if ((p2->p_tracep = p1->p_tracep) != NULL) 262 VREF(p2->p_tracep); 263 } 264 #endif 265 266 /* 267 * set priority of child to be that of parent 268 */ 269 p2->p_estcpu = p1->p_estcpu; 270 271 /* 272 * This begins the section where we must prevent the parent 273 * from being swapped. 274 */ 275 p1->p_flag |= P_NOSWAP; 276 277 /* 278 * Set return values for child before vm_fork, 279 * so they can be copied to child stack. 280 * We return parent pid, and mark as child in retval[1]. 281 * NOTE: the kernel stack may be at a different location in the child 282 * process, and thus addresses of automatic variables (including retval) 283 * may be invalid after vm_fork returns in the child process. 284 */ 285 retval[0] = p1->p_pid; 286 retval[1] = 1; 287 if (vm_fork(p1, p2, isvfork)) { 288 /* 289 * Child process. Set start time and get to work. 290 */ 291 (void) splclock(); 292 p2->p_stats->p_start = time; 293 (void) spl0(); 294 p2->p_acflag = AFORK; 295 return (0); 296 } 297 298 /* 299 * Make child runnable and add to run queue. 300 */ 301 (void) splhigh(); 302 p2->p_stat = SRUN; 303 setrunqueue(p2); 304 (void) spl0(); 305 306 /* 307 * Now can be swapped. 308 */ 309 p1->p_flag &= ~P_NOSWAP; 310 311 /* 312 * Preserve synchronization semantics of vfork. If waiting for 313 * child to exec or exit, set P_PPWAIT on child, and sleep on our 314 * proc (in case of exit). 315 */ 316 if (isvfork) 317 while (p2->p_flag & P_PPWAIT) 318 tsleep(p1, PWAIT, "ppwait", 0); 319 320 /* 321 * Return child pid to parent process, 322 * marking us as parent via retval[1]. 323 */ 324 retval[0] = p2->p_pid; 325 retval[1] = 0; 326 return (0); 327 } 328