system/FileDescriptor: add methods EnableCloseOnExec(), DisableCloseOnExec()

src/system/FileDescriptor.cxx

 /*
- * Copyright (C) 2012-2015 Max Kellermann <max.kellermann@gmail.com>
+ * Copyright (C) 2012-2017 Max Kellermann <max.kellermann@gmail.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -126,6 +126,24 @@ FileDescriptor::SetBlocking() noexcept
 	fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);
 }
 
+void
+FileDescriptor::EnableCloseOnExec() noexcept
+{
+	assert(IsDefined());
+
+	const int old_flags = fcntl(fd, F_GETFD, 0);
+	fcntl(fd, F_SETFD, old_flags | FD_CLOEXEC);
+}
+
+void
+FileDescriptor::DisableCloseOnExec() noexcept
+{
+	assert(IsDefined());
+
+	const int old_flags = fcntl(fd, F_GETFD, 0);
+	fcntl(fd, F_SETFD, old_flags & ~FD_CLOEXEC);
+}
+
 #endif
 
 #ifdef USE_EVENTFD

src/system/FileDescriptor.hxx

 /*
- * Copyright (C) 2012-2015 Max Kellermann <max.kellermann@gmail.com>
+ * Copyright (C) 2012-2017 Max Kellermann <max.kellermann@gmail.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -115,6 +115,18 @@ public:
 	void SetBlocking() noexcept;
 
 	/**
+	 * Auto-close this file descriptor when a new program is
+	 * executed.
+	 */
+	void EnableCloseOnExec() noexcept;
+
+	/**
+	 * Do not auto-close this file descriptor when a new program
+	 * is executed.
+	 */
+	void DisableCloseOnExec() noexcept;
+
+	/**
 	 * Duplicate the file descriptor onto the given file descriptor.
 	 */
 	bool Duplicate(int new_fd) const noexcept {