Re: [patch 7/8] fdmap v2 - implement sys_socket2

From: Davide Libenzi
Date: Fri Jun 08 2007 - 14:07:42 EST

On Fri, 8 Jun 2007, Theodore Tso wrote:

> On Thu, Jun 07, 2007 at 03:40:14PM -0700, Davide Libenzi wrote:
> > Yes. Files with the CLOFORK and CLOEXEC flag do not count for fork and
> > exec copies.
> > I was also planning on doing it in __put_unused_fd(), every time
> > fmap->count goes to zero. But get_random_int() is not as cheap as I
> > thought. If we use a cheaper (although less secure) function to mix pid &
> > jiffies, we could do it even in there.
> Um, how cheap do you need it? get_random_int() is actually pretty
> cheep, since it was designed to be usable by the networking stack for
> sequence numbers for TCP packets; and it's not like sys_close() or
> sys_open() is a majorly critical path, is it? If the concern is
> increasing the potential hold time, I suppose you could have the
> exactly two callers of __put_unused_fd() (sys_close() and
> put_unused_fd()) call get_random_int() before grabbing the
> current->files->file_lock spinlock,

I'm actually using get_random_int() in the slow path (fmap creation time).
It does a few things get_random_int(), and one of those is an MD4 transform.
This does not need to be super secure (the Unix allocator has been
exactly predicatble for years), so maybe a cheaper combination of the
previous base (generated with get_random_int) together with jiffies and
pid is enough. I really would not want to put something like an MD4
transform in that path.

- Davide

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at