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/util.h"           /* tilde_expand() */
  58 #include "lib/lock.h"
  59
  60 #include "src/wtools.h" /* query_dialog() */
  61
  62 #define BUF_SIZE 255
  63 #define PID_BUF_SIZE 10
  64
  65 struct lock_s {
  66     char *who;
  67     pid_t pid;
  68 };
  69
  70 /** \fn static char * lock_build_name (void)
  71  *  \brief builds user@host.domain.pid string (need to be freed)
  72  *  \return a pointer to lock filename
  73  */
  74 static char *
  75 lock_build_name (void)
  76 {
  77     char host[BUF_SIZE];
  78     const char *user = NULL;
  79     struct passwd *pw;
  80
  81     pw = getpwuid (getuid ());
  82     if (pw) user = pw->pw_name;
  83     if (!user) user = getenv ("USER");
  84     if (!user) user = getenv ("USERNAME");
  85     if (!user) user = getenv ("LOGNAME");
  86     if (!user) user = "";
  87
  88     /** \todo Use FQDN, no clean interface, so requires lot of code */
  89     if (gethostname (host, BUF_SIZE - 1) == -1)
  90         *host = '\0';
  91
  92     return g_strdup_printf ("%s@%s.%d", user, host, (int) getpid ());
  93 }
  94
  95 static char *
  96 lock_build_symlink_name (const char *fname)
  97 {
  98     char *fname_copy, *symlink_name;
  99     char absolute_fname[PATH_MAX];
 100
 101     if (mc_realpath (fname, absolute_fname) == NULL)
 102         return NULL;
 103
 104     fname = x_basename (absolute_fname);
 105     fname_copy = g_strdup (fname);
 106     absolute_fname[fname - absolute_fname] = '\0';
 107     symlink_name = g_strconcat (absolute_fname, ".#", fname_copy, (char *) NULL);
 108     g_free (fname_copy);
 109
 110     return symlink_name;
 111 }
 112
 113 /* Extract pid from user@host.domain.pid string */
 114 static struct lock_s *
 115 lock_extract_info (const char *str)
 116 {
 117     size_t i, len;
 118     const char *p, *s;
 119     static char pid[PID_BUF_SIZE], who[BUF_SIZE];
 120     static struct lock_s lock;
 121
 122     len = strlen (str);
 123
 124     for (p = str + len - 1; p >= str; p--)
 125         if (*p == '.')
 126             break;
 127
 128     /* Everything before last '.' is user@host */
 129     i = 0;
 130     for (s = str; s < p && i < BUF_SIZE; s++)
 131         who[i++] = *s;
 132     who[i] = '\0';
 133
 134     /* Treat text between '.' and ':' or '\0' as pid */
 135     i = 0;
 136     for (p = p + 1; (p < str + len) && (*p != ':') && (i < PID_BUF_SIZE); p++)
 137         pid[i++] = *p;
 138     pid[i] = '\0';
 139
 140     lock.pid = (pid_t) atol (pid);
 141     lock.who = who;
 142     return &lock;
 143 }
 144
 145 /* Extract user@host.domain.pid from lock file (static string)  */
 146 static char *
 147 lock_get_info (const char *lockfname)
 148 {
 149     int cnt;
 150     static char buf[BUF_SIZE];
 151
 152     cnt = readlink (lockfname, buf, BUF_SIZE - 1);
 153     if (cnt == -1 || *buf == '\0')
 154         return NULL;
 155     buf[cnt] = '\0';
 156     return buf;
 157 }
 158
 159
 160 /* Tries to raise file lock
 161    Returns 1 on success,  0 on failure, -1 if abort
 162    Warning: Might do screen refresh and lose edit->force */
 163 int
 164 lock_file (const char *fname)
 165 {
 166     char *lockfname, *newlock, *msg, *lock;
 167     struct stat statbuf;
 168     struct lock_s *lockinfo;
 169     gboolean symlink_ok;
 170
 171     /* Just to be sure (and don't lock new file) */
 172     if (fname == NULL || *fname == '\0')
 173         return 0;
 174
 175     fname = tilde_expand (fname);
 176
 177     /* Locking on VFS is not supported */
 178     if (!vfs_file_is_local (fname))
 179     {
 180         g_free (fname);
 181         return 0;
 182     }
 183
 184     /* Check if already locked */
 185     lockfname = lock_build_symlink_name (fname);
 186     g_free (fname);
 187     if (lockfname == NULL)
 188         return 0;
 189
 190     if (lstat (lockfname, &statbuf) == 0) {
 191         lock = lock_get_info (lockfname);
 192         if (lock == NULL) {
 193             g_free (lockfname);
 194             return 0;
 195         }
 196         lockinfo = lock_extract_info (lock);
 197
 198         /* Check if locking process alive, ask user if required */
 199         if (lockinfo->pid == 0
 200             || !(kill (lockinfo->pid, 0) == -1 && errno == ESRCH)) {
 201             msg =
 202                 g_strdup_printf (_
 203                                  ("File \"%s\" is already being edited.\n"
 204                                   "User: %s\nProcess ID: %d"), x_basename (lockfname) + 2,
 205                                  lockinfo->who, (int) lockinfo->pid);
 206             /* TODO: Implement "Abort" - needs to rewind undo stack */
 207             switch (query_dialog
 208                     (_("File locked"), msg, D_NORMAL, 2, _("&Grab lock"),
 209                      _("&Ignore lock"))) {
 210             case 0:
 211                 break;
 212             case 1:
 213             case -1:
 214                 g_free (lockfname);
 215                 g_free (msg);
 216                 return 0;
 217             }
 218             g_free (msg);
 219         }
 220         unlink (lockfname);
 221     }
 222
 223     /* Create lock symlink */
 224     newlock = lock_build_name ();
 225     symlink_ok = (symlink (newlock, lockfname) != -1);
 226     g_free (newlock);
 227     g_free (lockfname);
 228
 229     return symlink_ok ? 1 : 0;
 230 }
 231
 232 /* Lowers file lock if possible
 233    Always returns 0 */
 234 int
 235 unlock_file (const char *fname)
 236 {
 237     char *lockfname, *lock;
 238     struct stat statbuf;
 239
 240     /* Just to be sure */
 241     if (fname == NULL || *fname == '\0')
 242         return 0;
 243
 244     fname = tilde_expand (fname);
 245     lockfname = lock_build_symlink_name (fname);
 246     g_free (fname);
 247
 248     if (lockfname == NULL)
 249         return 0;
 250
 251     /* Check if lock exists */
 252     if (lstat (lockfname, &statbuf) == -1) {
 253         g_free (lockfname);
 254         return 0;
 255     }
 256
 257     lock = lock_get_info (lockfname);
 258     if (lock != NULL) {
 259         /* Don't touch if lock is not ours */
 260         if (lock_extract_info (lock)->pid != getpid ()) {
 261             g_free (lockfname);
 262             return 0;
 263         }
 264     }
 265
 266     /* Remove lock */
 267     unlink (lockfname);
 268     g_free (lockfname);
 269     return 0;
 270 }