linux-kernel - Re: [PATCH] nextfd(2)

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Message-ID: <CA+55aFwCaekbk7VocaU0_O=7fDgJRBXUiQYvoYh1GDMicbCtow@mail.gmail.com>
Date:	Sun, 1 Apr 2012 10:20:59 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	drepper@...il.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] nextfd(2)

On Sun, Apr 1, 2012 at 5:57 AM, Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> BSD added closefrom(fd) which is OK for this exact purpose but suboptimal
> on the bigger scale. closefrom(2) does only close(2) (obviously :-)
> closefrom(2) siletly ignores errors from close(2) which in theory is not OK
> for userspace.
>
> So, don't add closefrom(2), add nextfd(2).

I don't disagree with this, but I don't think it's worth a new file of
its own - I think it should go next to dup() and friends (currently in
fs/fcntl.h).

Also, I think you should:

 (a) at a minimum use the bitmap.  It's easy:

    struct fdtable *fdt;

    rcu_read_lock();
    fdt = files_fdtable(current->files);
    .. maximum fd in fdt->max_fds ...
    .. you have the bitmap in fdt->open_fds ..

 (b) I'd also suggest you add a "flag" argument and have at least one
bit option for "search for next *free* file table entry". I'm not sure
anybody wants it, but it is kind of the same operation, and having a
"flags" field means that it's extensible in the future if people want
to find the next cloexec fd or whatever. Or if they just want to find
the *last* fd, or something.

But I think the concept makes sense.

                               Linus
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