netdev - Re: [PATCHv6 1/3] tun: export underlying socket

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Message-Id: <200911031341.31622.arnd@arndb.de>
Date:	Tue, 3 Nov 2009 13:41:31 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, mingo@...e.hu,
	linux-mm@...ck.org, akpm@...ux-foundation.org, hpa@...or.com,
	gregory.haskins@...il.com, Rusty Russell <rusty@...tcorp.com.au>,
	s.hetze@...ux-ag.com
Subject: Re: [PATCHv6 1/3] tun: export underlying socket

On Tuesday 03 November 2009, Michael S. Tsirkin wrote:
> > What was your reason for changing?
> 
> It turns out socket structure is really bound to specific a file, so we
> can not have 2 files referencing the same socket.  Instead, as I say
> above, it's possible to make sendmsg/recvmsg work on tap file directly.

Ah, I see.

> I have implemented this (patch below), but decided to go with the simple
> thing first.  Since no userspace-visible changes are involved, let's do
> this by small steps: it will be easier to figure out when vhost
> is upstream.

This may even make it easier for me to do the same with macvtap
if I resume work on that.

> @@ -416,8 +422,8 @@ int sock_map_fd(struct socket *sock, int flags)
>  
>  static struct socket *sock_from_file(struct file *file, int *err)
>  {
> -       if (file->f_op == &socket_file_ops)
> -               return file->private_data;      /* set in sock_map_fd */
> +       if (file->f_op->get_socket)
> +               return file->f_op->get_socket(file);
>  
>         *err = -ENOTSOCK;

Or maybe do both (socket_file_ops and get_socket), to avoid an indirect
function call.

	Arnd <><
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