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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
