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 */ 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/map.h> 44 #include <sys/filedesc.h> 45 #include <sys/kernel.h> 46 #include <sys/malloc.h> 47 #include <sys/proc.h> 48 #include <sys/resourcevar.h> 49 #include <sys/vnode.h> 50 #include <sys/file.h> 51 #include <sys/acct.h> 52 #include <sys/ktrace.h> 53 54 struct fork_args { 55 int dummy; 56 }; 57 /* ARGSUSED */ 58 int 59 fork(p, uap, retval) 60 struct proc *p; 61 struct fork_args *uap; 62 int retval[]; 63 { 64 65 return (fork1(p, 0, retval)); 66 } 67 68 /* ARGSUSED */ 69 int 70 vfork(p, uap, retval) 71 struct proc *p; 72 struct fork_args *uap; 73 int retval[]; 74 { 75 76 return (fork1(p, 1, retval)); 77 } 78 79 int nprocs = 1; /* process 0 */ 80 81 int 82 fork1(p1, isvfork, retval) 83 register struct proc *p1; 84 int isvfork, retval[]; 85 { 86 register struct proc *p2; 87 register uid_t uid; 88 struct proc *newproc; 89 struct proc **hash; 90 int count; 91 static int nextpid, pidchecked = 0; 92 93 /* 94 * Although process entries are dynamically created, we still keep 95 * a global limit on the maximum number we will create. Don't allow 96 * a nonprivileged user to use the last process; don't let root 97 * exceed the limit. The variable nprocs is the current number of 98 * processes, maxproc is the limit. 99 */ 100 uid = p1->p_cred->p_ruid; 101 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 102 tablefull("proc"); 103 return (EAGAIN); 104 } 105 /* 106 * Increment the count of procs running with this uid. Don't allow 107 * a nonprivileged user to exceed their current limit. 108 */ 109 count = chgproccnt(uid, 1); 110 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 111 (void)chgproccnt(uid, -1); 112 return (EAGAIN); 113 } 114 115 /* Allocate new proc. */ 116 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 117 118 /* 119 * Find an unused process ID. We remember a range of unused IDs 120 * ready to use (from nextpid+1 through pidchecked-1). 121 */ 122 nextpid++; 123 retry: 124 /* 125 * If the process ID prototype has wrapped around, 126 * restart somewhat above 0, as the low-numbered procs 127 * tend to include daemons that don't exit. 128 */ 129 if (nextpid >= PID_MAX) { 130 nextpid = 100; 131 pidchecked = 0; 132 } 133 if (nextpid >= pidchecked) { 134 int doingzomb = 0; 135 136 pidchecked = PID_MAX; 137 /* 138 * Scan the active and zombie procs to check whether this pid 139 * is in use. Remember the lowest pid that's greater 140 * than nextpid, so we can avoid checking for a while. 141 */ 142 p2 = (struct proc *)allproc; 143 again: 144 for (; p2 != NULL; p2 = p2->p_next) { 145 while (p2->p_pid == nextpid || 146 p2->p_pgrp->pg_id == nextpid) { 147 nextpid++; 148 if (nextpid >= pidchecked) 149 goto retry; 150 } 151 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 152 pidchecked = p2->p_pid; 153 if (p2->p_pgrp->pg_id > nextpid && 154 pidchecked > p2->p_pgrp->pg_id) 155 pidchecked = p2->p_pgrp->pg_id; 156 } 157 if (!doingzomb) { 158 doingzomb = 1; 159 p2 = zombproc; 160 goto again; 161 } 162 } 163 164 165 /* 166 * Link onto allproc (this should probably be delayed). 167 * Heavy use of volatile here to prevent the compiler from 168 * rearranging code. Yes, it *is* terribly ugly, but at least 169 * it works. 170 */ 171 nprocs++; 172 p2 = newproc; 173 #define Vp2 ((volatile struct proc *)p2) 174 Vp2->p_stat = SIDL; /* protect against others */ 175 Vp2->p_pid = nextpid; 176 /* 177 * This is really: 178 * p2->p_next = allproc; 179 * allproc->p_prev = &p2->p_next; 180 * p2->p_prev = &allproc; 181 * allproc = p2; 182 * The assignment via allproc is legal since it is never NULL. 183 */ 184 *(volatile struct proc **)&Vp2->p_next = allproc; 185 *(volatile struct proc ***)&allproc->p_prev = 186 (volatile struct proc **)&Vp2->p_next; 187 *(volatile struct proc ***)&Vp2->p_prev = &allproc; 188 allproc = Vp2; 189 #undef Vp2 190 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 191 192 /* Insert on the hash chain. */ 193 hash = &pidhash[PIDHASH(p2->p_pid)]; 194 p2->p_hash = *hash; 195 *hash = p2; 196 197 /* 198 * Make a proc table entry for the new process. 199 * Start by zeroing the section of proc that is zero-initialized, 200 * then copy the section that is copied directly from the parent. 201 */ 202 bzero(&p2->p_startzero, 203 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 204 bcopy(&p1->p_startcopy, &p2->p_startcopy, 205 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 206 207 /* 208 * Duplicate sub-structures as needed. 209 * Increase reference counts on shared objects. 210 * The p_stats and p_sigacts substructs are set in vm_fork. 211 */ 212 p2->p_flag = P_INMEM; 213 if (p1->p_flag & P_PROFIL) 214 startprofclock(p2); 215 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 216 M_SUBPROC, M_WAITOK); 217 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 218 p2->p_cred->p_refcnt = 1; 219 crhold(p1->p_ucred); 220 221 /* bump references to the text vnode (for procfs) */ 222 p2->p_textvp = p1->p_textvp; 223 if (p2->p_textvp) 224 VREF(p2->p_textvp); 225 226 p2->p_fd = fdcopy(p1); 227 /* 228 * If p_limit is still copy-on-write, bump refcnt, 229 * otherwise get a copy that won't be modified. 230 * (If PL_SHAREMOD is clear, the structure is shared 231 * copy-on-write.) 232 */ 233 if (p1->p_limit->p_lflags & PL_SHAREMOD) 234 p2->p_limit = limcopy(p1->p_limit); 235 else { 236 p2->p_limit = p1->p_limit; 237 p2->p_limit->p_refcnt++; 238 } 239 240 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 241 p2->p_flag |= P_CONTROLT; 242 if (isvfork) 243 p2->p_flag |= P_PPWAIT; 244 p2->p_pgrpnxt = p1->p_pgrpnxt; 245 p1->p_pgrpnxt = p2; 246 p2->p_pptr = p1; 247 p2->p_osptr = p1->p_cptr; 248 if (p1->p_cptr) 249 p1->p_cptr->p_ysptr = p2; 250 p1->p_cptr = p2; 251 #ifdef KTRACE 252 /* 253 * Copy traceflag and tracefile if enabled. 254 * If not inherited, these were zeroed above. 255 */ 256 if (p1->p_traceflag&KTRFAC_INHERIT) { 257 p2->p_traceflag = p1->p_traceflag; 258 if ((p2->p_tracep = p1->p_tracep) != NULL) 259 VREF(p2->p_tracep); 260 } 261 #endif 262 263 /* 264 * This begins the section where we must prevent the parent 265 * from being swapped. 266 */ 267 p1->p_flag |= P_NOSWAP; 268 /* 269 * Set return values for child before vm_fork, 270 * so they can be copied to child stack. 271 * We return parent pid, and mark as child in retval[1]. 272 * NOTE: the kernel stack may be at a different location in the child 273 * process, and thus addresses of automatic variables (including retval) 274 * may be invalid after vm_fork returns in the child process. 275 */ 276 retval[0] = p1->p_pid; 277 retval[1] = 1; 278 if (vm_fork(p1, p2, isvfork)) { 279 /* 280 * Child process. Set start time and get to work. 281 */ 282 (void) splclock(); 283 p2->p_stats->p_start = time; 284 (void) spl0(); 285 p2->p_acflag = AFORK; 286 return (0); 287 } 288 289 /* 290 * Make child runnable and add to run queue. 291 */ 292 (void) splhigh(); 293 p2->p_stat = SRUN; 294 setrunqueue(p2); 295 (void) spl0(); 296 297 /* 298 * Now can be swapped. 299 */ 300 p1->p_flag &= ~P_NOSWAP; 301 302 /* 303 * Preserve synchronization semantics of vfork. If waiting for 304 * child to exec or exit, set P_PPWAIT on child, and sleep on our 305 * proc (in case of exit). 306 */ 307 if (isvfork) 308 while (p2->p_flag & P_PPWAIT) 309 tsleep(p1, PWAIT, "ppwait", 0); 310 311 /* 312 * Return child pid to parent process, 313 * marking us as parent via retval[1]. 314 */ 315 retval[0] = p2->p_pid; 316 retval[1] = 0; 317 return (0); 318 } 319