Re: [PATCH] nextfd(2)

[Colin Walters <walters@verbum.org>]

On Wed, 2012-04-04 at 09:31 -0700, KOSAKI Motohiro wrote:

> Ideally possible. but practically impossible. 2) people don't use a their
> own malloc. they only uses open sources alternative malloc. And, I think
> you have too narrowing concern. Even though malloc people adds a workaround,
> the standard inhibit to use it

What do you mean?  If as hpa says, the maintainer of e.g. google
tcmalloc added a call to pthread_atfork(), then code which uses
opendir() would start working.

>  and people may continue to use more dangerous
> RLIM_NOFILE loop. 1) I haven't seen _practical_ userland software uses such
> linux internal hacking. Almost all major software can run on multiple OSs.

Except that if you're using /proc/self/fd, you're already relying on
Linux-specific functionality.  So it's not burdensome to use "struct
linux_dirent" and O_DIRECTORY either.

In GLib we're presently doing the regular /proc+opendir() under
#ifdef __linux__:
http://git.gnome.org/browse/glib/tree/glib/gspawn.c#n932

Now I'd happily switch to hpa's fdwalk() implementation if I was aware
of someone using glib in combination with an alternative malloc hitting
this problem.

Basically I think hpa is right here, and it's not really worth adding
a new system call.

The thing is, even if it were added today, since we need to run on old
kernels, we'd have to carry the code to use the /proc trick
approximately forever.  And in the end all nextfd() would accomplish
would be a *third* case in the already messy ifdefs/fallbacks
in the various implementations of process spawning.