Re: O_CLOEXEC: An alternate proposal

From: Eric Dumazet
Date: Fri Jun 08 2007 - 05:21:25 EST

On Fri, 8 Jun 2007 03:47:12 -0400 (EDT)
"Daniel Colascione" <danc@xxxxxxxxxxxxxxxx> wrote:

> Hey, this is my first post to linux-kernel, so please be kind. :-)

Welcome Daniel

> Linus Torvalds wrote on May 31:
> > I'm with Uli on this one. "Stateful" stuff is bad. It's essentially
> > impossible to handle with libraries - either the library would have to
> > explciitly always turn the state the way _it_ needs it, or the library
> > will do the wrogn thing.
> I agree that stateful stuff is generally not very elegant,
> but I think it's a win here -- we wouldn't have to create any
> new APIs except for the state-setting stuff.
> The state just has to be thread-local.
> If it's thread-local, a library, say, glibc,
> can use code like this:
> /* Internal library function */
> old_fd_flags = kernel_default_fd_flags(FD_CLOEXEC | FD_RANDFD);

<race here if a signal handler runs some user code messing with a thread-local fd_flags >

> event_fd = super_duper_event_polling_mechanism_fd();
> kernel_default_fd_flags(old_fd_flags);
> I think that's a lot cleaner than augmenting every
> present and future fd-creating syscall to take some kind
> of flags parameter and adding some kind of funny dup().

Thats funny, you probably missed Linus syscall_indirect() proposal,
which is basically doing the thing but with one syscall (so no races, and faster)

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