1 files changed, 145 insertions, 0 deletions
diff --git a/src/lib/fs/lockfile.c b/src/lib/fs/lockfile.c
new file mode 100644
index 0000000000..933ff1e02f
--- /dev/null
+++ b/src/lib/fs/lockfile.c
@@ -0,0 +1,145 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file lockfile.c
+ *
+ * \brief Implements lock files to prevent two Tor processes from using the
+ * same data directory at the same time.
+ **/
+
+#include "orconfig.h"
+#include "lib/fs/files.h"
+#include "lib/fs/lockfile.h"
+#include "lib/log/log.h"
+#include "lib/log/util_bug.h"
+#include "lib/malloc/malloc.h"
+
+#ifdef HAVE_SYS_FILE_H
+#include <sys/file.h>
+#endif
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+#ifdef _WIN32
+#include <windows.h>
+#include <sys/locking.h>
+#endif
+
+#include <errno.h>
+#include <string.h>
+
+/** Represents a lockfile on which we hold the lock. */
+struct tor_lockfile_t {
+  /** Name of the file */
+  char *filename;
+  /** File descriptor used to hold the file open */
+  int fd;
+};
+
+/** Try to get a lock on the lockfile <b>filename</b>, creating it as
+ * necessary.  If someone else has the lock and <b>blocking</b> is true,
+ * wait until the lock is available.  Otherwise return immediately whether
+ * we succeeded or not.
+ *
+ * Set *<b>locked_out</b> to true if somebody else had the lock, and to false
+ * otherwise.
+ *
+ * Return a <b>tor_lockfile_t</b> on success, NULL on failure.
+ *
+ * (Implementation note: because we need to fall back to fcntl on some
+ *  platforms, these locks are per-process, not per-thread.  If you want
+ *  to do in-process locking, use tor_mutex_t like a normal person.
+ *  On Windows, when <b>blocking</b> is true, the maximum time that
+ *  is actually waited is 10 seconds, after which NULL is returned
+ *  and <b>locked_out</b> is set to 1.)
+ */
+tor_lockfile_t *
+tor_lockfile_lock(const char *filename, int blocking, int *locked_out)
+{
+  tor_lockfile_t *result;
+  int fd;
+  *locked_out = 0;
+
+  log_info(LD_FS, "Locking \"%s\"", filename);
+  fd = tor_open_cloexec(filename, O_RDWR|O_CREAT|O_TRUNC, 0600);
+  if (fd < 0) {
+    log_warn(LD_FS,"Couldn't open \"%s\" for locking: %s", filename,
+             strerror(errno));
+    return NULL;
+  }
+
+#ifdef _WIN32
+  _lseek(fd, 0, SEEK_SET);
+  if (_locking(fd, blocking ? _LK_LOCK : _LK_NBLCK, 1) < 0) {
+    if (errno != EACCES && errno != EDEADLOCK)
+      log_warn(LD_FS,"Couldn't lock \"%s\": %s", filename, strerror(errno));
+    else
+      *locked_out = 1;
+    close(fd);
+    return NULL;
+  }
+#elif defined(HAVE_FLOCK)
+  if (flock(fd, LOCK_EX|(blocking ? 0 : LOCK_NB)) < 0) {
+    if (errno != EWOULDBLOCK)
+      log_warn(LD_FS,"Couldn't lock \"%s\": %s", filename, strerror(errno));
+    else
+      *locked_out = 1;
+    close(fd);
+    return NULL;
+  }
+#else
+  {
+    struct flock lock;
+    memset(&lock, 0, sizeof(lock));
+    lock.l_type = F_WRLCK;
+    lock.l_whence = SEEK_SET;
+    if (fcntl(fd, blocking ? F_SETLKW : F_SETLK, &lock) < 0) {
+      if (errno != EACCES && errno != EAGAIN)
+        log_warn(LD_FS, "Couldn't lock \"%s\": %s", filename, strerror(errno));
+      else
+        *locked_out = 1;
+      close(fd);
+      return NULL;
+    }
+  }
+#endif /* defined(_WIN32) || ... */
+
+  result = tor_malloc(sizeof(tor_lockfile_t));
+  result->filename = tor_strdup(filename);
+  result->fd = fd;
+  return result;
+}
+
+/** Release the lock held as <b>lockfile</b>. */
+void
+tor_lockfile_unlock(tor_lockfile_t *lockfile)
+{
+  tor_assert(lockfile);
+
+  log_info(LD_FS, "Unlocking \"%s\"", lockfile->filename);
+#ifdef _WIN32
+  _lseek(lockfile->fd, 0, SEEK_SET);
+  if (_locking(lockfile->fd, _LK_UNLCK, 1) < 0) {
+    log_warn(LD_FS,"Error unlocking \"%s\": %s", lockfile->filename,
+             strerror(errno));
+  }
+#elif defined(HAVE_FLOCK)
+  if (flock(lockfile->fd, LOCK_UN) < 0) {
+    log_warn(LD_FS, "Error unlocking \"%s\": %s", lockfile->filename,
+             strerror(errno));
+  }
+#else
+  /* Closing the lockfile is sufficient. */
+#endif /* defined(_WIN32) || ... */
+
+  close(lockfile->fd);
+  lockfile->fd = -1;
+  tor_free(lockfile->filename);
+  tor_free(lockfile);
+}