lib/lock.c

   1 /*
   2    File locking
   3
   4    Copyright (C) 2003, 2004, 2005, 2006, 2007, 2011
   5    The Free Software Foundation, Inc.
   6
   7    Written by:
   8    Adam Byrtek, 2003
   9
  10    This file is part of the Midnight Commander.
  11
  12    The Midnight Commander is free software: you can redistribute it
  13    and/or modify it under the terms of the GNU General Public License as
  14    published by the Free Software Foundation, either version 3 of the License,
  15    or (at your option) any later version.
  16
  17    The Midnight Commander is distributed in the hope that it will be useful,
  18    but WITHOUT ANY WARRANTY; without even the implied warranty of
  19    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20    GNU General Public License for more details.
  21
  22    You should have received a copy of the GNU General Public License
  23    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  24  */
  25
  26 /** \file
  27  *  \brief Source: file locking
  28  *  \author Adam Byrtek
  29  *  \date 2003
  30  *
  31  *  Locking scheme is based on a documentation found
  32  *  in JED editor sources. Abstract from lock.c file (by John E. Davis):
  33  *
  34  *  The basic idea here is quite simple.  Whenever a buffer is attached to
  35  *  a file, and that buffer is modified, then attempt to lock the
  36  *  file. Moreover, before writing to a file for any reason, lock the
  37  *  file. The lock is really a protocol respected and not a real lock.
  38  *  The protocol is this: If in the directory of the file is a
  39  *  symbolic link with name ".#FILE", the FILE is considered to be locked
  40  *  by the process specified by the link.
  41  */
  42
  43 #include <config.h>
  44
  45 #include <signal.h>             /* kill() */
  46 #include <stdio.h>
  47 #include <stdarg.h>
  48 #include <sys/types.h>
  49 #include <unistd.h>
  50 #include <string.h>
  51 #include <ctype.h>
  52 #include <errno.h>
  53 #include <sys/stat.h>
  54 #include <pwd.h>
  55 #include <stdlib.h>
  56
  57 #include "lib/global.h"
  58 #include "lib/vfs/vfs.h"
  59 #include "lib/util.h"           /* tilde_expand() */
  60 #include "lib/lock.h"
  61 #include "lib/widget.h"         /* query_dialog() */
  62
  63 /*** global variables ****************************************************************************/
  64
  65 /*** file scope macro definitions ****************************************************************/
  66
  67 #define BUF_SIZE 255
  68 #define PID_BUF_SIZE 10
  69
  70 /*** file scope type declarations ****************************************************************/
  71
  72 struct lock_s
  73 {
  74     char *who;
  75     pid_t pid;
  76 };
  77
  78 /*** file scope variables ************************************************************************/
  79
  80 /*** file scope functions ************************************************************************/
  81 /* --------------------------------------------------------------------------------------------- */
  82 /** \fn static char * lock_build_name (void)
  83  *  \brief builds user@host.domain.pid string (need to be freed)
  84  *  \return a pointer to lock filename
  85  */
  86
  87 static char *
  88 lock_build_name (void)
  89 {
  90     char host[BUF_SIZE];
  91     const char *user = NULL;
  92     struct passwd *pw;
  93
  94     pw = getpwuid (getuid ());
  95     if (pw)
  96         user = pw->pw_name;
  97     if (!user)
  98         user = getenv ("USER");
  99     if (!user)
 100         user = getenv ("USERNAME");
 101     if (!user)
 102         user = getenv ("LOGNAME");
 103     if (!user)
 104         user = "";
 105
 106     /** \todo Use FQDN, no clean interface, so requires lot of code */
 107     if (gethostname (host, BUF_SIZE - 1) == -1)
 108         *host = '\0';
 109
 110     return g_strdup_printf ("%s@%s.%d", user, host, (int) getpid ());
 111 }
 112
 113 /* --------------------------------------------------------------------------------------------- */
 114
 115 static char *
 116 lock_build_symlink_name (const vfs_path_t * fname_vpath)
 117 {
 118     const char *elpath, *str_filename;
 119     char *str_dirname, *symlink_name;
 120
 121     /* get first path piece */
 122     elpath = vfs_path_get_by_index (fname_vpath, 0)->path;
 123
 124     str_filename = g_basename (elpath);
 125     str_dirname = g_dirname (elpath);
 126
 127     symlink_name = g_strconcat (str_dirname, PATH_SEP_STR ".#", str_filename, (char *) NULL);
 128     g_free (str_dirname);
 129     return symlink_name;
 130 }
 131
 132 /* --------------------------------------------------------------------------------------------- */
 133 /**
 134  * Extract pid from user@host.domain.pid string
 135  */
 136
 137 static struct lock_s *
 138 lock_extract_info (const char *str)
 139 {
 140     size_t i, len;
 141     const char *p, *s;
 142     static char pid[PID_BUF_SIZE], who[BUF_SIZE];
 143     static struct lock_s lock;
 144
 145     len = strlen (str);
 146
 147     for (p = str + len - 1; p >= str; p--)
 148         if (*p == '.')
 149             break;
 150
 151     /* Everything before last '.' is user@host */
 152     i = 0;
 153     for (s = str; s < p && i < BUF_SIZE; s++)
 154         who[i++] = *s;
 155     who[i] = '\0';
 156
 157     /* Treat text between '.' and ':' or '\0' as pid */
 158     i = 0;
 159     for (p = p + 1; (p < str + len) && (*p != ':') && (i < PID_BUF_SIZE); p++)
 160         pid[i++] = *p;
 161     pid[i] = '\0';
 162
 163     lock.pid = (pid_t) atol (pid);
 164     lock.who = who;
 165     return &lock;
 166 }
 167
 168 /* --------------------------------------------------------------------------------------------- */
 169 /**
 170  * Extract user@host.domain.pid from lock file (static string)
 171  */
 172
 173 static char *
 174 lock_get_info (const char *lockfname)
 175 {
 176     int cnt;
 177     static char buf[BUF_SIZE];
 178
 179     cnt = readlink (lockfname, buf, BUF_SIZE - 1);
 180     if (cnt == -1 || *buf == '\0')
 181         return NULL;
 182     buf[cnt] = '\0';
 183     return buf;
 184 }
 185
 186 /* --------------------------------------------------------------------------------------------- */
 187 /*** public functions ****************************************************************************/
 188 /* --------------------------------------------------------------------------------------------- */
 189
 190 /* Tries to raise file lock
 191    Returns 1 on success,  0 on failure, -1 if abort
 192    Warning: Might do screen refresh and lose edit->force */
 193
 194 int
 195 lock_file (const vfs_path_t * fname_vpath)
 196 {
 197     char *lockfname = NULL, *newlock, *msg, *lock;
 198     struct stat statbuf;
 199     struct lock_s *lockinfo;
 200     gboolean is_local;
 201     gboolean symlink_ok = FALSE;
 202     const char *elpath;
 203
 204     if (fname_vpath == NULL)
 205         return 0;
 206
 207     elpath = vfs_path_get_by_index (fname_vpath, 0)->path;
 208     /* Just to be sure (and don't lock new file) */
 209     if (*elpath == '\0')
 210         return 0;
 211
 212     /* Locking on VFS is not supported */
 213     is_local = vfs_file_is_local (fname_vpath);
 214     if (is_local)
 215     {
 216         /* Check if already locked */
 217         lockfname = lock_build_symlink_name (fname_vpath);
 218     }
 219
 220     if (!is_local || lockfname == NULL)
 221         return 0;
 222
 223     if (lstat (lockfname, &statbuf) == 0)
 224     {
 225         lock = lock_get_info (lockfname);
 226         if (lock == NULL)
 227             goto ret;
 228         lockinfo = lock_extract_info (lock);
 229
 230         /* Check if locking process alive, ask user if required */
 231         if (lockinfo->pid == 0 || !(kill (lockinfo->pid, 0) == -1 && errno == ESRCH))
 232         {
 233             msg =
 234                 g_strdup_printf (_
 235                                  ("File \"%s\" is already being edited.\n"
 236                                   "User: %s\nProcess ID: %d"), x_basename (lockfname) + 2,
 237                                  lockinfo->who, (int) lockinfo->pid);
 238             /* TODO: Implement "Abort" - needs to rewind undo stack */
 239             switch (query_dialog
 240                     (_("File locked"), msg, D_NORMAL, 2, _("&Grab lock"), _("&Ignore lock")))
 241             {
 242             case 0:
 243                 break;
 244             case 1:
 245             case -1:
 246                 g_free (msg);
 247                 goto ret;
 248                 break;          /* FIXME: unneeded? */
 249             }
 250             g_free (msg);
 251         }
 252         unlink (lockfname);
 253     }
 254
 255     /* Create lock symlink */
 256     newlock = lock_build_name ();
 257     symlink_ok = (symlink (newlock, lockfname) != -1);
 258     g_free (newlock);
 259
 260   ret:
 261     g_free (lockfname);
 262     return symlink_ok ? 1 : 0;
 263 }
 264
 265 /* --------------------------------------------------------------------------------------------- */
 266 /**
 267  * Lowers file lock if possible
 268  * @returns  Always 0
 269  */
 270
 271 int
 272 unlock_file (const vfs_path_t * fname_vpath)
 273 {
 274     char *lockfname, *lock;
 275     struct stat statbuf;
 276     const char *elpath;
 277
 278     if (fname_vpath == NULL)
 279         return 0;
 280
 281     elpath = vfs_path_get_by_index (fname_vpath, 0)->path;
 282     /* Just to be sure (and don't lock new file) */
 283     if (*elpath == '\0')
 284         return 0;
 285
 286     lockfname = lock_build_symlink_name (fname_vpath);
 287
 288     if (lockfname == NULL)
 289         return 0;
 290
 291     /* Check if lock exists */
 292     if (lstat (lockfname, &statbuf) == -1)
 293         goto ret;
 294
 295     lock = lock_get_info (lockfname);
 296     if (lock != NULL)
 297     {
 298         /* Don't touch if lock is not ours */
 299         if (lock_extract_info (lock)->pid != getpid ())
 300             goto ret;
 301     }
 302
 303     /* Remove lock */
 304     unlink (lockfname);
 305
 306   ret:
 307     g_free (lockfname);
 308     return 0;
 309 }
 310
 311 /* --------------------------------------------------------------------------------------------- */