contrib/tcsh-6/dotlock.c

   1 /*      $NetBSD: dotlock.c,v 1.11 2009/10/21 01:07:46 snj Exp $ */
   2
   3 /*
   4  * Copyright (c) 1996 Christos Zoulas.  All rights reserved.
   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  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  */
  26 #include "sh.h"
  27 RCSID("$tcsh: dotlock.c,v 3.3 2014/03/09 00:11:54 christos Exp $");
  28
  29 #include <stdio.h>
  30 #ifndef O_SYNC
  31 #define O_SYNC  0
  32 #endif
  33
  34 #include "dotlock.h"
  35
  36 static int create_exclusive(const char *);
  37 /*
  38  * Create a unique file. O_EXCL does not really work over NFS so we follow
  39  * the following trick: [Inspired by  S.R. van den Berg]
  40  *
  41  * - make a mostly unique filename and try to create it.
  42  * - link the unique filename to our target
  43  * - get the link count of the target
  44  * - unlink the mostly unique filename
  45  * - if the link count was 2, then we are ok; else we've failed.
  46  */
  47 static int
  48 create_exclusive(const char *fname)
  49 {
  50         char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1];
  51         const char *ptr;
  52         struct timeval tv;
  53         pid_t pid;
  54         size_t ntries, cookie;
  55         int fd, serrno;
  56         struct stat st;
  57
  58         (void)gettimeofday(&tv, NULL);
  59         (void)gethostname(hostname, sizeof(hostname));
  60         hostname[sizeof(hostname) - 1] = '\0';
  61         pid = getpid();
  62
  63         cookie = pid ^ tv.tv_usec;
  64
  65         /*
  66          * We generate a semi-unique filename, from hostname.(pid ^ usec)
  67          */
  68         if ((ptr = strrchr(fname, '/')) == NULL)
  69                 ptr = fname;
  70         else
  71                 ptr++;
  72
  73         (void)snprintf(path, sizeof(path), "%.*s.%s.%lx",
  74             (int)(ptr - fname), fname, hostname, (u_long)cookie);
  75
  76         /*
  77          * We try to create the unique filename.
  78          */
  79         for (ntries = 0; ntries < 5; ntries++) {
  80                 fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0);
  81                 if (fd != -1) {
  82                         (void)close(fd);
  83                         break;
  84                 }
  85                 else if (errno == EEXIST)
  86                         continue;
  87                 else
  88                         return -1;
  89         }
  90
  91         /*
  92          * We link the path to the name
  93          */
  94         if (link(path, fname) == -1)
  95                 goto bad;
  96
  97         /*
  98          * Note that we stat our own exclusively created name, not the
  99          * destination, since the destination can be affected by others.
 100          */
 101         if (stat(path, &st) == -1)
 102                 goto bad;
 103
 104         (void)unlink(path);
 105
 106         /*
 107          * If the number of links was two (one for the unique file and one
 108          * for the lock), we've won the race
 109          */
 110         if (st.st_nlink != 2) {
 111                 errno = EEXIST;
 112                 return -1;
 113         }
 114         return 0;
 115
 116 bad:
 117         serrno = errno;
 118         (void)unlink(path);
 119         errno = serrno;
 120         return -1;
 121 }
 122
 123 /*
 124  * fname -- Pathname to lock
 125  * pollinterval -- Interval (miliseconds) to check for lock, -1 return
 126  */
 127 int
 128 dot_lock(const char *fname, int pollinterval)
 129 {
 130         char path[MAXPATHLEN];
 131         sigset_t nset, oset;
 132         int retval;
 133
 134         (void)sigemptyset(&nset);
 135         (void)sigaddset(&nset, SIGHUP);
 136         (void)sigaddset(&nset, SIGINT);
 137         (void)sigaddset(&nset, SIGQUIT);
 138         (void)sigaddset(&nset, SIGTERM);
 139         (void)sigaddset(&nset, SIGTTIN);
 140         (void)sigaddset(&nset, SIGTTOU);
 141         (void)sigaddset(&nset, SIGTSTP);
 142         (void)sigaddset(&nset, SIGCHLD);
 143
 144         (void)snprintf(path, sizeof(path), "%s.lock", fname);
 145
 146         retval = -1;
 147         for (;;) {
 148                 handle_pending_signals();
 149                 (void)sigprocmask(SIG_BLOCK, &nset, &oset);
 150                 if (create_exclusive(path) != -1) {
 151                         (void)sigprocmask(SIG_SETMASK, &oset, NULL);
 152                         retval = 0;
 153                         break;
 154                 }
 155                 else
 156                         (void)sigprocmask(SIG_SETMASK, &oset, NULL);
 157
 158                 if (errno != EEXIST)
 159                         break;
 160
 161                 if (pollinterval) {
 162                         if (pollinterval == -1) {
 163                                 errno = EEXIST;
 164                                 break;
 165                         }
 166                         (void)usleep((unsigned int)pollinterval * 1000);
 167                 }
 168         }
 169         handle_pending_signals();
 170         return retval;
 171 }
 172
 173 void
 174 dot_unlock(const char *fname)
 175 {
 176         char path[MAXPATHLEN];
 177
 178         (void)snprintf(path, sizeof(path), "%s.lock", fname);
 179         (void)unlink(path);
 180 }