linux-kernel - Re: O_CLOEXEC: An alternate proposal

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Date:	Fri, 8 Jun 2007 11:19:09 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"Daniel Colascione" <danc@...rillpress.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: O_CLOEXEC: An alternate proposal

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

http://marc.info/?l=linux-kernel&m=118124716616552&w=2

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