src/common/lockfile.cpp

   1 /*
   2  * Copyright (C) 2012 David Goulet <dgoulet@efficios.com>
   3  * Copyright (C) 2013 Jérémie Galarneau <jeremie.galarneau@efficios.com>
   4  *
   5  * SPDX-License-Identifier: LGPL-2.1-only
   6  *
   7  */
   8
   9 #include <common/error.hpp>
  10 #include <common/lockfile.hpp>
  11 #include <common/macros.hpp>
  12
  13 #include <fcntl.h>
  14
  15 #ifdef HAVE_FLOCK
  16
  17 #include <sys/file.h>
  18
  19 static int lock_file(const char *filepath, int fd)
  20 {
  21         int ret;
  22
  23         /*
  24          * Attempt to lock the file. If this fails, there is
  25          * already a process using the same lock file running
  26          * and we should exit.
  27          */
  28         ret = flock(fd, LOCK_EX | LOCK_NB);
  29         if (ret == -1) {
  30                 /* EWOULDBLOCK are expected if the file is locked: don't spam the logs. */
  31                 if (errno != EWOULDBLOCK) {
  32                         PERROR("Failed to apply lock on lock file: file_path=`%s`", filepath);
  33                 }
  34         }
  35
  36         return ret;
  37 }
  38
  39 #else /* HAVE_FLOCK */
  40
  41 static int lock_file(const char *filepath, int fd)
  42 {
  43         int ret;
  44         struct flock lock = {};
  45
  46         lock.l_whence = SEEK_SET;
  47         lock.l_type = F_WRLCK;
  48
  49         /*
  50          * Attempt to lock the file. If this fails, there is
  51          * already a process using the same lock file running
  52          * and we should exit.
  53          */
  54         ret = fcntl(fd, F_SETLK, &lock);
  55         if (ret == -1) {
  56                 /* EAGAIN and EACCESS are expected if the file is locked: don't spam the logs. */
  57                 if (errno != EAGAIN && errno != EACCES) {
  58                         PERROR("Failed to set lock on lock file: file_path=`%s`", filepath);
  59                 }
  60         }
  61
  62         return ret;
  63 }
  64
  65 #endif /* HAVE_FLOCK */
  66
  67 int utils_create_lock_file(const char *filepath)
  68 {
  69         int ret, fd;
  70
  71         LTTNG_ASSERT(filepath);
  72
  73         fd = open(filepath, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
  74         if (fd < 0) {
  75                 PERROR("Failed to open lock file `%s`", filepath);
  76                 fd = -1;
  77                 goto error;
  78         }
  79
  80         /*
  81          * Attempt to lock the file. If this fails, there is already a process using the same lock
  82          * file running and we should exit.
  83          *
  84          * lock_file is chosen based on the build configuration, see implementations above.
  85          */
  86         ret = lock_file(filepath, fd);
  87         if (ret == -1) {
  88                 ERR("Could not get lock file `%s`, another instance is running.", filepath);
  89
  90                 if (close(fd)) {
  91                         PERROR("Failed to close lock file fd: fd=%d", fd);
  92                 }
  93
  94                 fd = ret;
  95                 goto error;
  96         }
  97
  98         DBG_FMT("Acquired lock file: file_path={}", filepath);
  99
 100 error:
 101         return fd;
 102 }