linux-kernel - Re: [GIT PULL] pidfd updates

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Message-ID: <20230425-sardinen-bespannt-c19a6bb8e74e@brauner>
Date:   Tue, 25 Apr 2023 14:08:54 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] pidfd updates

On Mon, Apr 24, 2023 at 01:35:03PM -0700, Linus Torvalds wrote:
> On Mon, Apr 24, 2023 at 1:24 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > But I really think a potentially much nicer model would have been to
> > extend our "get_unused_fd_flags()" model.
> >
> > IOW, we could have instead marked the 'struct file *' in the file
> > descriptor table as being "not ready yet".
> 
> Maybe that isn't worth it just for pdfd, but I have this feeling that
> it might make some other code simpler too.
> 
> That pidfd case isn't the only one that has to carry both a file
> pointer and a fd around.
> 
> Looking around, I get the feeling that quite a lot of users of
> "fd_install()" might actually have been happier if they could just
> install it early, and then just have a "fd_expose(fd)" for the success
> case, and for the error cases have "put_unused_fd(fd)" also do the
> fput on the file descriptor even if the low bit was set. One less
> thing to worry about.
> 
> I dunno. Maybe not worth it. That "two return values" just made me go "Eww".

I'm not fond of "two return values" - in C at least - as well I think
open-coding get_unused_fd() is pretty nasty as well...
Let me see...