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From: Arnd Bergmann <arnd@arndb.de>
To: virtualization@lists.linux-foundation.org
Subject: Re: [PATCHv6 1/3] tun: export underlying socket
Date: Tue, 3 Nov 2009 13:12:33 +0100
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Cc: "Michael S. Tsirkin" <mst@redhat.com>, netdev@vger.kernel.org,
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On Monday 02 November 2009, Michael S. Tsirkin wrote:
> Tun device looks similar to a packet socket
> in that both pass complete frames from/to userspace.
> 
> This patch fills in enough fields in the socket underlying tun driver
> to support sendmsg/recvmsg operations, and message flags
> MSG_TRUNC and MSG_DONTWAIT, and exports access to this socket
> to modules.  Regular read/write behaviour is unchanged.
> 
> This way, code using raw sockets to inject packets
> into a physical device, can support injecting
> packets into host network stack almost without modification.
> 
> First user of this interface will be vhost virtualization
> accelerator.

You mentioned before that you wanted to export the socket
using some ioctl function returning an open file descriptor,
which seemed to be a cleaner approach than this one.

What was your reason for changing?

> index 3f5fd52..404abe0 100644
> --- a/include/linux/if_tun.h
> +++ b/include/linux/if_tun.h
> @@ -86,4 +86,18 @@ struct tun_filter {
>         __u8   addr[0][ETH_ALEN];
>  };
>  
> +#ifdef __KERNEL__
> +#if defined(CONFIG_TUN) || defined(CONFIG_TUN_MODULE)
> +struct socket *tun_get_socket(struct file *);
> +#else
> +#include <linux/err.h>
> +#include <linux/errno.h>
> +struct file;
> +struct socket;
> +static inline struct socket *tun_get_socket(struct file *f)
> +{
> +       return ERR_PTR(-EINVAL);
> +}
> +#endif /* CONFIG_TUN */
> +#endif /* __KERNEL__ */
>  #endif /* __IF_TUN_H */

Is this a leftover from testing? Exporting the function for !__KERNEL__
seems pointless.

	Arnd <><