kern_fork.c revision 1.37
1 /* $NetBSD: kern_fork.c,v 1.37 1998/02/05 07:59:50 mrg 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 #include <sys/vmmeter.h> 57 58 #include <sys/syscallargs.h> 59 60 #include <vm/vm.h> 61 62 #if defined(UVM) 63 #include <uvm/uvm_extern.h> 64 #endif 65 66 int nprocs = 1; /* process 0 */ 67 68 /*ARGSUSED*/ 69 int 70 sys_fork(p, v, retval) 71 struct proc *p; 72 void *v; 73 register_t *retval; 74 { 75 76 return (fork1(p, 0, retval, NULL)); 77 } 78 79 /* 80 * vfork(2) system call compatible with 4.4BSD (i.e. BSD with Mach VM). 81 * Address space is not shared, but parent is blocked until child exit. 82 */ 83 /*ARGSUSED*/ 84 int 85 sys_vfork(p, v, retval) 86 struct proc *p; 87 void *v; 88 register_t *retval; 89 { 90 91 return (fork1(p, FORK_PPWAIT, retval, NULL)); 92 } 93 94 /* 95 * New vfork(2) system call for NetBSD, which implements original 3BSD vfork(2) 96 * semantics. Address space is shared, and parent is blocked until child exit. 97 */ 98 /*ARGSUSED*/ 99 int 100 sys___vfork14(p, v, retval) 101 struct proc *p; 102 void *v; 103 register_t *retval; 104 { 105 106 return (fork1(p, FORK_PPWAIT|FORK_SHAREVM, retval, NULL)); 107 } 108 109 int 110 fork1(p1, flags, retval, rnewprocp) 111 register struct proc *p1; 112 int flags; 113 register_t *retval; 114 struct proc **rnewprocp; 115 { 116 register struct proc *p2; 117 register uid_t uid; 118 struct proc *newproc; 119 int count; 120 static int nextpid, pidchecked = 0; 121 122 /* 123 * Although process entries are dynamically created, we still keep 124 * a global limit on the maximum number we will create. Don't allow 125 * a nonprivileged user to use the last process; don't let root 126 * exceed the limit. The variable nprocs is the current number of 127 * processes, maxproc is the limit. 128 */ 129 uid = p1->p_cred->p_ruid; 130 if ((nprocs >= maxproc - 1 && uid != 0) || nprocs >= maxproc) { 131 tablefull("proc"); 132 return (EAGAIN); 133 } 134 135 /* 136 * Increment the count of procs running with this uid. Don't allow 137 * a nonprivileged user to exceed their current limit. 138 */ 139 count = chgproccnt(uid, 1); 140 if (uid != 0 && count > p1->p_rlimit[RLIMIT_NPROC].rlim_cur) { 141 (void)chgproccnt(uid, -1); 142 return (EAGAIN); 143 } 144 145 /* Allocate new proc. */ 146 MALLOC(newproc, struct proc *, sizeof(struct proc), M_PROC, M_WAITOK); 147 148 /* 149 * Find an unused process ID. We remember a range of unused IDs 150 * ready to use (from nextpid+1 through pidchecked-1). 151 */ 152 nextpid++; 153 retry: 154 /* 155 * If the process ID prototype has wrapped around, 156 * restart somewhat above 0, as the low-numbered procs 157 * tend to include daemons that don't exit. 158 */ 159 if (nextpid >= PID_MAX) { 160 nextpid = 100; 161 pidchecked = 0; 162 } 163 if (nextpid >= pidchecked) { 164 int doingzomb = 0; 165 166 pidchecked = PID_MAX; 167 /* 168 * Scan the active and zombie procs to check whether this pid 169 * is in use. Remember the lowest pid that's greater 170 * than nextpid, so we can avoid checking for a while. 171 */ 172 p2 = allproc.lh_first; 173 again: 174 for (; p2 != 0; p2 = p2->p_list.le_next) { 175 while (p2->p_pid == nextpid || 176 p2->p_pgrp->pg_id == nextpid) { 177 nextpid++; 178 if (nextpid >= pidchecked) 179 goto retry; 180 } 181 if (p2->p_pid > nextpid && pidchecked > p2->p_pid) 182 pidchecked = p2->p_pid; 183 if (p2->p_pgrp->pg_id > nextpid && 184 pidchecked > p2->p_pgrp->pg_id) 185 pidchecked = p2->p_pgrp->pg_id; 186 } 187 if (!doingzomb) { 188 doingzomb = 1; 189 p2 = zombproc.lh_first; 190 goto again; 191 } 192 } 193 194 nprocs++; 195 p2 = newproc; 196 p2->p_stat = SIDL; /* protect against others */ 197 p2->p_pid = nextpid; 198 LIST_INSERT_HEAD(&allproc, p2, p_list); 199 p2->p_forw = p2->p_back = NULL; /* shouldn't be necessary */ 200 LIST_INSERT_HEAD(PIDHASH(p2->p_pid), p2, p_hash); 201 202 /* 203 * Make a proc table entry for the new process. 204 * Start by zeroing the section of proc that is zero-initialized, 205 * then copy the section that is copied directly from the parent. 206 */ 207 bzero(&p2->p_startzero, 208 (unsigned) ((caddr_t)&p2->p_endzero - (caddr_t)&p2->p_startzero)); 209 bcopy(&p1->p_startcopy, &p2->p_startcopy, 210 (unsigned) ((caddr_t)&p2->p_endcopy - (caddr_t)&p2->p_startcopy)); 211 212 /* 213 * Duplicate sub-structures as needed. 214 * Increase reference counts on shared objects. 215 * The p_stats and p_sigacts substructs are set in vm_fork. 216 */ 217 p2->p_flag = P_INMEM | (p1->p_flag & P_SUGID); 218 p2->p_emul = p1->p_emul; 219 if (p1->p_flag & P_PROFIL) 220 startprofclock(p2); 221 MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred), 222 M_SUBPROC, M_WAITOK); 223 bcopy(p1->p_cred, p2->p_cred, sizeof(*p2->p_cred)); 224 p2->p_cred->p_refcnt = 1; 225 crhold(p1->p_ucred); 226 227 /* bump references to the text vnode (for procfs) */ 228 p2->p_textvp = p1->p_textvp; 229 if (p2->p_textvp) 230 VREF(p2->p_textvp); 231 232 p2->p_fd = fdcopy(p1); 233 /* 234 * If p_limit is still copy-on-write, bump refcnt, 235 * otherwise get a copy that won't be modified. 236 * (If PL_SHAREMOD is clear, the structure is shared 237 * copy-on-write.) 238 */ 239 if (p1->p_limit->p_lflags & PL_SHAREMOD) 240 p2->p_limit = limcopy(p1->p_limit); 241 else { 242 p2->p_limit = p1->p_limit; 243 p2->p_limit->p_refcnt++; 244 } 245 246 if (p1->p_session->s_ttyvp != NULL && p1->p_flag & P_CONTROLT) 247 p2->p_flag |= P_CONTROLT; 248 if (flags & FORK_PPWAIT) 249 p2->p_flag |= P_PPWAIT; 250 LIST_INSERT_AFTER(p1, p2, p_pglist); 251 p2->p_pptr = p1; 252 LIST_INSERT_HEAD(&p1->p_children, p2, p_sibling); 253 LIST_INIT(&p2->p_children); 254 255 #ifdef KTRACE 256 /* 257 * Copy traceflag and tracefile if enabled. 258 * If not inherited, these were zeroed above. 259 */ 260 if (p1->p_traceflag&KTRFAC_INHERIT) { 261 p2->p_traceflag = p1->p_traceflag; 262 if ((p2->p_tracep = p1->p_tracep) != NULL) 263 VREF(p2->p_tracep); 264 } 265 #endif 266 267 /* 268 * This begins the section where we must prevent the parent 269 * from being swapped. 270 */ 271 PHOLD(p1); 272 273 /* 274 * Finish creating the child process. It will return through a 275 * different path later. 276 */ 277 #if defined(UVM) 278 uvm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 279 #else 280 vm_fork(p1, p2, (flags & FORK_SHAREVM) ? TRUE : FALSE); 281 #endif 282 283 /* 284 * Make child runnable, set start time, and add to run queue. 285 */ 286 (void) splstatclock(); 287 p2->p_stats->p_start = time; 288 p2->p_acflag = AFORK; 289 p2->p_stat = SRUN; 290 setrunqueue(p2); 291 (void) spl0(); 292 293 /* 294 * Now can be swapped. 295 */ 296 PRELE(p1); 297 298 /* 299 * Update stats now that we know the fork was successful. 300 */ 301 #if defined(UVM) 302 uvmexp.forks++; 303 if (flags & FORK_PPWAIT) 304 uvmexp.forks_ppwait++; 305 if (flags & FORK_SHAREVM) 306 uvmexp.forks_sharevm++; 307 #else 308 cnt.v_forks++; 309 if (flags & FORK_PPWAIT) 310 cnt.v_forks_ppwait++; 311 if (flags & FORK_SHAREVM) 312 cnt.v_forks_sharevm++; 313 #endif 314 315 /* 316 * Pass a pointer to the new process to the caller. 317 */ 318 if (rnewprocp != NULL) 319 *rnewprocp = p2; 320 321 /* 322 * Preserve synchronization semantics of vfork. If waiting for 323 * child to exec or exit, set P_PPWAIT on child, and sleep on our 324 * proc (in case of exit). 325 */ 326 if (flags & FORK_PPWAIT) 327 while (p2->p_flag & P_PPWAIT) 328 tsleep(p1, PWAIT, "ppwait", 0); 329 330 /* 331 * Return child pid to parent process, 332 * marking us as parent via retval[1]. 333 */ 334 if (retval != NULL) { 335 retval[0] = p2->p_pid; 336 retval[1] = 0; 337 } 338 return (0); 339 } 340
Indexes created Tue Sep 23 14:10:03 GMT 2025