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
  28 #include <stdio.h>
  29 #ifndef O_SYNC
  30 #define O_SYNC  0
  31 #endif
  32
  33 #include "dotlock.h"
  34
  35 static int create_exclusive(const char *);
  36 /*
  37  * Create a unique file. O_EXCL does not really work over NFS so we follow
  38  * the following trick: [Inspired by  S.R. van den Berg]
  39  *
  40  * - make a mostly unique filename and try to create it.
  41  * - link the unique filename to our target
  42  * - get the link count of the target
  43  * - unlink the mostly unique filename
  44  * - if the link count was 2, then we are ok; else we've failed.
  45  */
  46 static int
  47 create_exclusive(const char *fname)
  48 {
  49         char path[MAXPATHLEN], hostname[MAXHOSTNAMELEN + 1];
  50         const char *ptr;
  51         struct timeval tv;
  52         pid_t pid;
  53         size_t ntries, cookie;
  54         int fd, serrno;
  55         struct stat st;
  56
  57         (void)gettimeofday(&tv, NULL);
  58         (void)gethostname(hostname, sizeof(hostname));
  59         hostname[sizeof(hostname) - 1] = '\0';
  60         pid = getpid();
  61
  62         cookie = pid ^ tv.tv_usec;
  63
  64         /*
  65          * We generate a semi-unique filename, from hostname.(pid ^ usec)
  66          */
  67         if ((ptr = strrchr(fname, '/')) == NULL)
  68                 ptr = fname;
  69         else
  70                 ptr++;
  71
  72         (void)snprintf(path, sizeof(path), "%.*s.%s.%lx",
  73             (int)(ptr - fname), fname, hostname, (u_long)cookie);
  74
  75         /*
  76          * We try to create the unique filename.
  77          */
  78         for (ntries = 0; ntries < 5; ntries++) {
  79                 fd = open(path, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL|O_SYNC, 0);
  80                 if (fd != -1) {
  81                         (void)close(fd);
  82                         break;
  83                 }
  84                 else if (errno == EEXIST)
  85                         continue;
  86                 else
  87                         return -1;
  88         }
  89
  90         /*
  91          * We link the path to the name
  92          */
  93         if (link(path, fname) == -1)
  94                 goto bad;
  95
  96         /*
  97          * Note that we stat our own exclusively created name, not the
  98          * destination, since the destination can be affected by others.
  99          */
 100         if (stat(path, &st) == -1)
 101                 goto bad;
 102
 103         (void)unlink(path);
 104
 105         /*
 106          * If the number of links was two (one for the unique file and one
 107          * for the lock), we've won the race
 108          */
 109         if (st.st_nlink != 2) {
 110                 errno = EEXIST;
 111                 return -1;
 112         }
 113         return 0;
 114
 115 bad:
 116         serrno = errno;
 117         (void)unlink(path);
 118         errno = serrno;
 119         return -1;
 120 }
 121
 122 /*
 123  * fname -- Pathname to lock
 124  * pollinterval -- Interval (miliseconds) to check for lock, -1 return
 125  */
 126 int
 127 dot_lock(const char *fname, int pollinterval)
 128 {
 129         char path[MAXPATHLEN];
 130         sigset_t nset, oset;
 131         int retval;
 132
 133         (void)sigemptyset(&nset);
 134         (void)sigaddset(&nset, SIGHUP);
 135         (void)sigaddset(&nset, SIGINT);
 136         (void)sigaddset(&nset, SIGQUIT);
 137         (void)sigaddset(&nset, SIGTERM);
 138         (void)sigaddset(&nset, SIGTTIN);
 139         (void)sigaddset(&nset, SIGTTOU);
 140         (void)sigaddset(&nset, SIGTSTP);
 141         (void)sigaddset(&nset, SIGCHLD);
 142
 143         (void)snprintf(path, sizeof(path), "%s.lock", fname);
 144
 145         retval = -1;
 146         for (;;) {
 147                 handle_pending_signals();
 148                 (void)sigprocmask(SIG_BLOCK, &nset, &oset);
 149                 if (create_exclusive(path) != -1) {
 150                         (void)sigprocmask(SIG_SETMASK, &oset, NULL);
 151                         retval = 0;
 152                         break;
 153                 }
 154                 else
 155                         (void)sigprocmask(SIG_SETMASK, &oset, NULL);
 156
 157                 if (errno != EEXIST)
 158                         break;
 159
 160                 if (pollinterval) {
 161                         if (pollinterval == -1) {
 162                                 errno = EEXIST;
 163                                 break;
 164                         }
 165                         (void)usleep((unsigned int)pollinterval * 1000);
 166                 }
 167         }
 168         handle_pending_signals();
 169         return retval;
 170 }
 171
 172 void
 173 dot_unlock(const char *fname)
 174 {
 175         char path[MAXPATHLEN];
 176
 177         (void)snprintf(path, sizeof(path), "%s.lock", fname);
 178         (void)unlink(path);
 179 }