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- lib/lock.c
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*/
1 /*
2 File locking
3
4 Copyright (C) 2003-2021
5 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 typedef struct
73 {
74 char *who;
75 pid_t pid;
76 } lock_s;
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)
/* ![[next]](../icons/right.png)
![[first]](../icons/n_first.png)
*/
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)
/* ![[previous]](../icons/left.png)
*/
117 {
118 const char *elpath;
119 char *str_filename, *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_path_get_basename (elpath);
125 str_dirname = g_path_get_dirname (elpath);
126 symlink_name = g_strconcat (str_dirname, PATH_SEP_STR ".#", str_filename, (char *) NULL);
127 g_free (str_dirname);
128 g_free (str_filename);
129
130 return symlink_name;
131 }
132
133 /* --------------------------------------------------------------------------------------------- */
134 /**
135 * Extract pid from user@host.domain.pid string
136 */
137
138 static lock_s *
139 lock_extract_info (const char *str)
/* */
140 {
141 size_t i, len;
142 const char *p, *s;
143 static char pid[PID_BUF_SIZE], who[BUF_SIZE];
144 static lock_s lock;
145
146 len = strlen (str);
147
148 for (p = str + len - 1; p >= str; p--)
149 if (*p == '.')
150 break;
151
152 /* Everything before last '.' is user@host */
153 i = 0;
154 for (s = str; i < BUF_SIZE && s < p; s++)
155 who[i++] = *s;
156 if (i == BUF_SIZE)
157 i--;
158 who[i] = '\0';
159
160 /* Treat text between '.' and ':' or '\0' as pid */
161 i = 0;
162 for (p = p + 1; i < PID_BUF_SIZE && p < str + len && *p != ':'; p++)
163 pid[i++] = *p;
164 if (i == PID_BUF_SIZE)
165 i--;
166 pid[i] = '\0';
167
168 lock.pid = (pid_t) atol (pid);
169 lock.who = who;
170 return &lock;
171 }
172
173 /* --------------------------------------------------------------------------------------------- */
174 /**
175 * Extract user@host.domain.pid from lock file (static string)
176 */
177
178 static const char *
179 lock_get_info (const char *lockfname)
/* */
180 {
181 ssize_t cnt;
182 static char buf[BUF_SIZE];
183
184 cnt = readlink (lockfname, buf, BUF_SIZE - 1);
185 if (cnt == -1 || *buf == '\0')
186 return NULL;
187 buf[cnt] = '\0';
188 return buf;
189 }
190
191 /* --------------------------------------------------------------------------------------------- */
192 /*** public functions ****************************************************************************/
193 /* --------------------------------------------------------------------------------------------- */
194
195 /* Tries to raise file lock
196 Returns 1 on success, 0 on failure, -1 if abort
197 Warning: Might do screen refresh and lose edit->force */
198
199 int
200 lock_file (const vfs_path_t * fname_vpath)
/* */
201 {
202 char *lockfname = NULL, *newlock, *msg;
203 struct stat statbuf;
204 lock_s *lockinfo;
205 gboolean is_local;
206 gboolean symlink_ok = FALSE;
207 const char *elpath;
208
209 if (fname_vpath == NULL)
210 return 0;
211
212 elpath = vfs_path_get_by_index (fname_vpath, 0)->path;
213 /* Just to be sure (and don't lock new file) */
214 if (*elpath == '\0')
215 return 0;
216
217 /* Locking on VFS is not supported */
218 is_local = vfs_file_is_local (fname_vpath);
219 if (is_local)
220 {
221 /* Check if already locked */
222 lockfname = lock_build_symlink_name (fname_vpath);
223 }
224
225 if (!is_local || lockfname == NULL)
226 return 0;
227
228 if (lstat (lockfname, &statbuf) == 0)
229 {
230 const char *lock;
231
232 lock = lock_get_info (lockfname);
233 if (lock == NULL)
234 goto ret;
235 lockinfo = lock_extract_info (lock);
236
237 /* Check if locking process alive, ask user if required */
238 if (lockinfo->pid == 0 || !(kill (lockinfo->pid, 0) == -1 && errno == ESRCH))
239 {
240 msg =
241 g_strdup_printf (_
242 ("File \"%s\" is already being edited.\n"
243 "User: %s\nProcess ID: %d"), x_basename (lockfname) + 2,
244 lockinfo->who, (int) lockinfo->pid);
245 /* TODO: Implement "Abort" - needs to rewind undo stack */
246 switch (query_dialog
247 (_("File locked"), msg, D_NORMAL, 2, _("&Grab lock"), _("&Ignore lock")))
248 {
249 case 0:
250 break;
251 case 1:
252 case -1:
253 default: /* Esc Esc */
254 g_free (msg);
255 goto ret;
256 }
257 g_free (msg);
258 }
259 unlink (lockfname);
260 }
261
262 /* Create lock symlink */
263 newlock = lock_build_name ();
264 symlink_ok = (symlink (newlock, lockfname) != -1);
265 g_free (newlock);
266
267 ret:
268 g_free (lockfname);
269 return symlink_ok ? 1 : 0;
270 }
271
272 /* --------------------------------------------------------------------------------------------- */
273 /**
274 * Lowers file lock if possible
275 * @return Always 0
276 */
277
278 int
279 unlock_file (const vfs_path_t * fname_vpath)
/* ![[last]](../icons/n_last.png)
*/
280 {
281 char *lockfname;
282 struct stat statbuf;
283 const char *elpath, *lock;
284
285 if (fname_vpath == NULL)
286 return 0;
287
288 elpath = vfs_path_get_by_index (fname_vpath, 0)->path;
289 /* Just to be sure (and don't lock new file) */
290 if (*elpath == '\0')
291 return 0;
292
293 lockfname = lock_build_symlink_name (fname_vpath);
294
295 if (lockfname == NULL)
296 return 0;
297
298 /* Check if lock exists */
299 if (lstat (lockfname, &statbuf) == -1)
300 goto ret;
301
302 lock = lock_get_info (lockfname);
303 if (lock != NULL)
304 {
305 /* Don't touch if lock is not ours */
306 if (lock_extract_info (lock)->pid != getpid ())
307 goto ret;
308 }
309
310 /* Remove lock */
311 unlink (lockfname);
312
313 ret:
314 g_free (lockfname);
315 return 0;
316 }
317
318 /* --------------------------------------------------------------------------------------------- */
![[bottom]](../icons/n_bottom.png){kind=icon}
*/