ctdb/server/ctdb_mutex_fcntl_helper.c

   1 /*
   2    CTDB mutex fcntl lock file helper
   3
   4    Copyright (C) Martin Schwenke 2015
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program; if not, see <http://www.gnu.org/licenses/>.
  18 */
  19
  20 #include "replace.h"
  21 #include "system/filesys.h"
  22 #include "system/network.h"
  23
  24 /* protocol.h is just needed for ctdb_sock_addr, which is used in system.h */
  25 #include "protocol/protocol.h"
  26 #include "common/system.h"
  27
  28 static char *progname = NULL;
  29
  30 static char fcntl_lock(const char *file, int *outfd)
  31 {
  32         int fd;
  33         struct flock lock;
  34
  35         fd = open(file, O_RDWR|O_CREAT, 0600);
  36         if (fd == -1) {
  37                 fprintf(stderr, "%s: Unable to open %s - (%s)\n",
  38                         progname, file, strerror(errno));
  39                 return '3';
  40         }
  41
  42         lock.l_type = F_WRLCK;
  43         lock.l_whence = SEEK_SET;
  44         lock.l_start = 0;
  45         lock.l_len = 1;
  46         lock.l_pid = 0;
  47
  48         if (fcntl(fd, F_SETLK, &lock) != 0) {
  49                 int saved_errno = errno;
  50                 close(fd);
  51                 fd = -1;
  52                 if (saved_errno == EACCES ||
  53                     saved_errno == EAGAIN) {
  54                         /* Lock contention, fail silently */
  55                         return '1';
  56                 }
  57
  58                 /* Log an error for any other failure */
  59                 fprintf(stderr,
  60                         "%s: Failed to get lock on '%s' - (%s)\n",
  61                         progname, file, strerror(saved_errno));
  62                 return '3';
  63         }
  64
  65         *outfd = fd;
  66
  67         return '0';
  68 }
  69
  70 int main(int argc, char *argv[])
  71 {
  72         char result;
  73         int ppid;
  74         const char *file = NULL;
  75         int fd = -1;
  76
  77         progname = argv[0];
  78
  79         if (argc != 2) {
  80                 fprintf(stderr, "Usage: %s <file>\n", progname);
  81                 exit(1);
  82         }
  83
  84         ppid = getppid();
  85
  86         if (ppid == 1) {
  87                 /* The original parent is gone and the process has
  88                  * been reparented to init.  This can happen if the
  89                  * helper is started just as the parent is killed
  90                  * during shutdown.  The error message doesn't need to
  91                  * be stellar, since there won't be anything around to
  92                  * capture and log it...
  93                  */
  94                 fprintf(stderr, "%s: PPID == 1\n", progname);
  95                 exit(1);
  96         }
  97
  98         file = argv[1];
  99
 100         result = fcntl_lock(file, &fd);
 101         sys_write(STDOUT_FILENO, &result, 1);
 102
 103         ctdb_wait_for_process_to_exit(ppid);
 104
 105         if (fd != -1) {
 106                 close(fd);
 107         }
 108
 109         return 0;
 110 }