lib/libutil/pidlock.c

   1 /*      $NetBSD: pidlock.c,v 1.16 2012/04/07 16:17:17 christos Exp $ */
   2
   3 /*
   4  * Copyright 1996, 1997 by Curt Sampson <cjs@NetBSD.org>.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  *
  12  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
  13  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  14  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  15  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE
  16  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  17  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  18  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  19  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  20  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  21  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  22  * SUCH DAMAGE.
  23  */
  24
  25 #include <sys/cdefs.h>
  26 #if defined(LIBC_SCCS) && !defined(lint)
  27 __RCSID("$NetBSD: pidlock.c,v 1.16 2012/04/07 16:17:17 christos Exp $");
  28 #endif /* LIBC_SCCS and not lint */
  29
  30 #include <sys/param.h>
  31 #include <sys/stat.h>
  32 #include <sys/types.h>
  33
  34 #include <assert.h>
  35 #include <errno.h>
  36 #include <fcntl.h>
  37 #include <signal.h>
  38 #include <stdio.h>
  39 #include <stdlib.h>
  40 #include <string.h>
  41 #include <unistd.h>
  42 #include <util.h>
  43 #include <paths.h>
  44
  45 /*
  46  * Create a lockfile. Return 0 when locked, -1 on error.
  47  */
  48 int
  49 pidlock(const char *lockfile, int flags, pid_t *locker, const char *info)
  50 {
  51         char    tempfile[MAXPATHLEN];
  52         char    hostname[MAXHOSTNAMELEN + 1];
  53         pid_t   pid2 = -1;
  54         struct  stat st;
  55         ssize_t n;
  56         int     f = -1, savee;
  57         char    s[256];
  58         char    *p;
  59         size_t  len;
  60
  61         _DIAGASSERT(lockfile != NULL);
  62         /* locker may be NULL */
  63         /* info may be NULL */
  64
  65
  66         if (gethostname(hostname, sizeof(hostname)))
  67                 return -1;
  68         hostname[sizeof(hostname) - 1] = '\0';
  69
  70         /*
  71          * Build a path to the temporary file.
  72          * We use the path with the PID and hostname appended.
  73          * XXX This is not thread safe.
  74          */
  75         if (snprintf(tempfile, sizeof(tempfile), "%s.%d.%s", lockfile,
  76             (int) getpid(), hostname) >= (int)sizeof(tempfile))  {
  77                 errno = ENAMETOOLONG;
  78                 return -1;
  79         }
  80
  81         /* Open it, write pid, hostname, info. */
  82         if ((f = open(tempfile, O_WRONLY|O_CREAT|O_TRUNC, 0600)) == -1)
  83                 goto out;
  84
  85         (void)snprintf(s, sizeof(s), "%10d\n", getpid());       /* pid */
  86         if (write(f, s, (size_t)11) != 11)
  87                 goto out;
  88
  89         if ((flags & PIDLOCK_USEHOSTNAME))  {           /* hostname */
  90                 len = strlen(hostname);
  91                 if ((size_t)write(f, hostname, len) != len
  92                     || write(f, "\n", (size_t)1) != 1)
  93                         goto out;
  94         }
  95         if (info)  {                                    /* info */
  96                 if (!(flags & PIDLOCK_USEHOSTNAME))  {
  97                         /* write blank line because there's no hostname */
  98                         if (write(f, "\n", (size_t)1) != 1)
  99                                 goto out;
 100                 }
 101                 len = strlen(info);
 102                 if ((size_t)write(f, info, len) != len ||
 103                     write(f, "\n", (size_t)1) != 1)
 104                         goto out;
 105         }
 106         (void)close(f);
 107         f = -1;
 108
 109         /* Hard link the temporary file to the real lock file. */
 110         /* This is an atomic operation. */
 111 lockfailed:
 112         while (link(tempfile, lockfile) == -1)  {
 113                 if (errno != EEXIST)
 114                         goto out;
 115                 /* Find out who has this lockfile. */
 116                 if ((f = open(lockfile, O_RDONLY, 0)) != -1)  {
 117                         if ((n = read(f, s, (size_t)11)) == -1)
 118                                 goto out;
 119                         if (n == 0) {
 120                                 errno = EINVAL;
 121                                 goto out;
 122                         }
 123                         pid2 = atoi(s);
 124                         if ((n = read(f, s, sizeof(s) - 2)) == -1)
 125                                 goto out;
 126                         if (n == 0)
 127                                 *s = '\0';
 128                         s[sizeof(s) - 1] = '\0';
 129                         if ((p = strchr(s, '\n')) != NULL)
 130                                 *p = '\0';
 131                         (void)close(f);
 132                         f = -1;
 133
 134                         if ((flags & PIDLOCK_USEHOSTNAME) == 0 ||
 135                             strcmp(s, hostname) == 0)  {
 136                                 if (kill(pid2, 0) == -1 && errno == ESRCH)  {
 137                                         /* process doesn't exist */
 138                                         (void)unlink(lockfile);
 139                                         continue;
 140                                 }
 141                         }
 142                 }
 143                 if (flags & PIDLOCK_NONBLOCK)  {
 144                         if (locker)
 145                                 *locker = pid2;
 146                         errno = EWOULDBLOCK;
 147                         goto out;
 148                 } else
 149                         sleep(5);
 150         }
 151         /*
 152          * Check to see that we really were successful (in case we're
 153          * using NFS) by making sure that something really is linked
 154          * to our tempfile (reference count is two).
 155          */
 156         if (stat(tempfile, &st) == -1)
 157                 goto out;
 158         if (st.st_nlink != 2)
 159                 goto lockfailed;
 160
 161         (void)unlink(tempfile);
 162         if (locker)
 163                 *locker = getpid();     /* return this process's PID on lock */
 164         errno = 0;
 165         return 0;
 166 out:
 167         savee = errno;
 168         if (f != -1)
 169                 (void)close(f);
 170         (void)unlink(tempfile);
 171         errno = savee;
 172         return -1;
 173 }
 174
 175 static int
 176 checktty(const char *tty)
 177 {
 178         char    ttyfile[MAXPATHLEN];
 179         struct stat sb;
 180
 181         (void)strlcpy(ttyfile, _PATH_DEV, sizeof(ttyfile));
 182         (void)strlcat(ttyfile, tty, sizeof(ttyfile));
 183
 184         /* make sure the tty exists */
 185         if (stat(ttyfile, &sb) == -1)
 186                 return -1;
 187         if (!S_ISCHR(sb.st_mode))  {
 188                 errno = EFTYPE;
 189                 return -1;
 190         }
 191         return 0;
 192 }
 193
 194 #define LOCKPATH        "/var/spool/lock/LCK.."
 195
 196 static char *
 197 makelock(char *buf, size_t bufsiz, const char *tty)
 198 {
 199         (void)strlcpy(buf, LOCKPATH, bufsiz);
 200         (void)strlcat(buf, tty, bufsiz);
 201         return buf;
 202 }
 203
 204 /*ARGSUSED*/
 205 int
 206 ttylock(const char *tty, int flags, pid_t *locker)
 207 {
 208         char    lockfile[MAXPATHLEN];
 209
 210         _DIAGASSERT(tty != NULL);
 211
 212         if (checktty(tty) != 0)
 213                 return -1;
 214
 215         /* do the lock */
 216         return pidlock(makelock(lockfile, sizeof(lockfile), tty),
 217             flags, locker, 0);
 218 }
 219
 220 int
 221 ttyunlock(const char *tty)
 222 {
 223         char    lockfile[MAXPATHLEN];
 224
 225         _DIAGASSERT(tty != NULL);
 226
 227         if (checktty(tty) != 0)
 228                 return -1;
 229
 230         /* remove the lock */
 231         return unlink(makelock(lockfile, sizeof(lockfile), tty));
 232 }