lib/lock.c

   1 /* file locking
   2
   3    Copyright (C) 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
   4
   5    Authors: 2003 Adam Byrtek
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20    02110-1301, USA.
  21
  22 */
  23
  24 /** \file
  25  *  \brief Source: file locking
  26  *  \author Adam Byrtek
  27  *  \date 2003
  28  *
  29  *  Locking scheme is based on a documentation found
  30  *  in JED editor sources. Abstract from lock.c file (by John E. Davis):
  31  *
  32  *  The basic idea here is quite simple.  Whenever a buffer is attached to
  33  *  a file, and that buffer is modified, then attempt to lock the
  34  *  file. Moreover, before writing to a file for any reason, lock the
  35  *  file. The lock is really a protocol respected and not a real lock.
  36  *  The protocol is this: If in the directory of the file is a
  37  *  symbolic link with name ".#FILE", the FILE is considered to be locked
  38  *  by the process specified by the link.
  39  */
  40
  41 #include <config.h>
  42
  43 #include <signal.h>             /* kill() */
  44 #include <stdio.h>
  45 #include <stdarg.h>
  46 #include <sys/types.h>
  47 #include <unistd.h>
  48 #include <string.h>
  49 #include <ctype.h>
  50 #include <errno.h>
  51 #include <sys/stat.h>
  52 #include <pwd.h>
  53 #include <stdlib.h>
  54
  55 #include "lib/global.h"
  56 #include "lib/vfs/mc-vfs/vfs.h"
  57 #include "lib/lock.h"
  58
  59 #include "src/wtools.h" /* query_dialog() */
  60
  61 #define BUF_SIZE 255
  62 #define PID_BUF_SIZE 10
  63
  64 struct lock_s {
  65     char *who;
  66     pid_t pid;
  67 };
  68
  69 /** \fn static char * lock_build_name (void)
  70  *  \brief builds user@host.domain.pid string (need to be freed)
  71  *  \return a pointer to lock filename
  72  */
  73 static char *
  74 lock_build_name (void)
  75 {
  76     char host[BUF_SIZE];
  77     const char *user = NULL;
  78     struct passwd *pw;
  79
  80     pw = getpwuid (getuid ());
  81     if (pw) user = pw->pw_name;
  82     if (!user) user = getenv ("USER");
  83     if (!user) user = getenv ("USERNAME");
  84     if (!user) user = getenv ("LOGNAME");
  85     if (!user) user = "";
  86
  87     /** \todo Use FQDN, no clean interface, so requires lot of code */
  88     if (gethostname (host, BUF_SIZE - 1) == -1)
  89         *host = '\0';
  90
  91     return g_strdup_printf ("%s@%s.%d", user, host, (int) getpid ());
  92 }
  93
  94 static char *
  95 lock_build_symlink_name (const char *fname)
  96 {
  97     char *fname_copy, *symlink_name;
  98     char absolute_fname[PATH_MAX];
  99
 100     if (mc_realpath (fname, absolute_fname) == NULL)
 101         return NULL;
 102
 103     fname = x_basename (absolute_fname);
 104     fname_copy = g_strdup (fname);
 105     absolute_fname[fname - absolute_fname] = '\0';
 106     symlink_name = g_strconcat (absolute_fname, ".#", fname_copy, (char *) NULL);
 107     g_free (fname_copy);
 108
 109     return symlink_name;
 110 }
 111
 112 /* Extract pid from user@host.domain.pid string */
 113 static struct lock_s *
 114 lock_extract_info (const char *str)
 115 {
 116     size_t i, len;
 117     const char *p, *s;
 118     static char pid[PID_BUF_SIZE], who[BUF_SIZE];
 119     static struct lock_s lock;
 120
 121     len = strlen (str);
 122
 123     for (p = str + len - 1; p >= str; p--)
 124         if (*p == '.')
 125             break;
 126
 127     /* Everything before last '.' is user@host */
 128     i = 0;
 129     for (s = str; s < p && i < BUF_SIZE; s++)
 130         who[i++] = *s;
 131     who[i] = '\0';
 132
 133     /* Treat text between '.' and ':' or '\0' as pid */
 134     i = 0;
 135     for (p = p + 1; (p < str + len) && (*p != ':') && (i < PID_BUF_SIZE); p++)
 136         pid[i++] = *p;
 137     pid[i] = '\0';
 138
 139     lock.pid = (pid_t) atol (pid);
 140     lock.who = who;
 141     return &lock;
 142 }
 143
 144 /* Extract user@host.domain.pid from lock file (static string)  */
 145 static char *
 146 lock_get_info (const char *lockfname)
 147 {
 148     int cnt;
 149     static char buf[BUF_SIZE];
 150
 151     cnt = readlink (lockfname, buf, BUF_SIZE - 1);
 152     if (cnt == -1 || *buf == '\0')
 153         return NULL;
 154     buf[cnt] = '\0';
 155     return buf;
 156 }
 157
 158
 159 /* Tries to raise file lock
 160    Returns 1 on success,  0 on failure, -1 if abort
 161    Warning: Might do screen refresh and lose edit->force */
 162 int
 163 lock_file (const char *fname)
 164 {
 165     char *lockfname, *newlock, *msg, *lock;
 166     struct stat statbuf;
 167     struct lock_s *lockinfo;
 168
 169     /* Just to be sure (and don't lock new file) */
 170     if (!fname || !*fname)
 171         return 0;
 172
 173     /* Locking on VFS is not supported */
 174     if (!vfs_file_is_local (fname))
 175         return 0;
 176
 177     /* Check if already locked */
 178     lockfname = lock_build_symlink_name (fname);
 179     if (lockfname == NULL)
 180         return 0;
 181     if (lstat (lockfname, &statbuf) == 0) {
 182         lock = lock_get_info (lockfname);
 183         if (!lock) {
 184             g_free (lockfname);
 185             return 0;
 186         }
 187         lockinfo = lock_extract_info (lock);
 188
 189         /* Check if locking process alive, ask user if required */
 190         if (!lockinfo->pid
 191             || !(kill (lockinfo->pid, 0) == -1 && errno == ESRCH)) {
 192             msg =
 193                 g_strdup_printf (_
 194                                  ("File \"%s\" is already being edited.\n"
 195                                   "User: %s\nProcess ID: %d"), x_basename (lockfname) + 2,
 196                                  lockinfo->who, (int) lockinfo->pid);
 197             /* TODO: Implement "Abort" - needs to rewind undo stack */
 198             switch (query_dialog
 199                     (_("File locked"), msg, D_NORMAL, 2, _("&Grab lock"),
 200                      _("&Ignore lock"))) {
 201             case 0:
 202                 break;
 203             case 1:
 204             case -1:
 205                 g_free (lockfname);
 206                 g_free (msg);
 207                 return 0;
 208             }
 209             g_free (msg);
 210         }
 211         unlink (lockfname);
 212     }
 213
 214     /* Create lock symlink */
 215     newlock = lock_build_name ();
 216     if (symlink (newlock, lockfname) == -1) {
 217         g_free (lockfname);
 218         g_free (newlock);
 219         return 0;
 220     }
 221
 222     g_free (lockfname);
 223     g_free (newlock);
 224     return 1;
 225 }
 226
 227 /* Lowers file lock if possible
 228    Always returns 0 */
 229 int
 230 unlock_file (const char *fname)
 231 {
 232     char *lockfname, *lock;
 233     struct stat statbuf;
 234
 235     /* Just to be sure */
 236     if (!fname || !*fname)
 237         return 0;
 238
 239     lockfname = lock_build_symlink_name (fname);
 240     if (lockfname == NULL)
 241         return 0;
 242
 243     /* Check if lock exists */
 244     if (lstat (lockfname, &statbuf) == -1) {
 245         g_free (lockfname);
 246         return 0;
 247     }
 248
 249     lock = lock_get_info (lockfname);
 250     if (lock) {
 251         /* Don't touch if lock is not ours */
 252         if (lock_extract_info (lock)->pid != getpid ()) {
 253             g_free (lockfname);
 254             return 0;
 255         }
 256     }
 257
 258     /* Remove lock */
 259     unlink (lockfname);
 260     g_free (lockfname);
 261     return 0;
 262 }