Bug 35173

Attachment #42466 [details] makes bus-test pass when given fds beyond 2 by the parent process (for instance under gdb). I'm splitting this off because it's not required to fix the bug it's attached to.

Colin Walters reviewed it and said:

> ::: dbus/dbus-message-private.h
> @@ +139,3 @@
>                                                  va_list          var_args);
> 
> +void _dbus_close_excess_fds(void);
> 
> Would prefer this lived in dbus-sysdeps.h.
> 
> ::: dbus/dbus-message-util.c
> @@ +182,3 @@
> +      closedir(d);
> +    }
> +#endif
> 
> This needs a non-#ifdef __linux__ implementation (and should probably fall back
> if the open of /prof/self/fd fails for some reason too).
> 
> This code is definitely scattered around; look at e.g.
> dbus-sysdeps-unix.c:3108 where we use sysconf (_SC_OPEN_MAX) and then a loop. 
> I think it'd be worth at least refactoring that bit to use this common
> function.
> 
> Also I suggest a better name is:
> 
> _dbus_close_nonstandard_fds ();
> 
> Or possibly
> 
> _dbus_close_fds_from (3); ?

to which I replied:

> (In reply to comment #8)
> > This needs a non-#ifdef __linux__ implementation (and should probably fall > back
> > if the open of /prof/self/fd fails for some reason too).
> 
> For this purpose, it doesn't need a fallback: it's meant to be an exact mirror
> of the check for leaked fds in the same file. Both are #ifdef __linux__ and
> only used in the regression tests.
> 
> > _dbus_close_nonstandard_fds ();
> 
> It'd be reasonable to put that function (and perhaps the leak check too) in
> sysdeps-util, though, and if placed in that location I agree it should be
> cross-platform.

Thinking about this again, it'd be better still if we made the check for leaked fds work like this:

* remember the initial set of fds
* do the test
* complain about any fds not found in the set we remembered

This would avoid breaking any tools that relied on having bonus fds open for their own purposes; for instance, Valgrind can be told to report to fd 3 if you don't want its output to get interleaved with your stdout and/or stderr.