Subject: Re: [PATCH v6 37/46] tun: move internal flag defines out of uapi

From: Jason Wang <[email-masked]>
Date: Fri, 28 Nov 2014 08:15:32 +0008

On Fri, Nov 28, 2014 at 4:10 AM, Michael S. Tsirkin <[email-masked]> 
wrote:
> TUN_ flags are internal and never exposed
> to userspace. Any application using it is almost
> certainly buggy.
> 
> Move them out to tun.c, we'll remove them in follow-up patches.
> 
> Signed-off-by: Michael S. Tsirkin <[email-masked]>
> ---
>  include/uapi/linux/if_tun.h | 16 ++--------
>  drivers/net/tun.c           | 74 
> ++++++++++++++-------------------------------
>  2 files changed, 26 insertions(+), 64 deletions(-)
> 
> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> index e9502dd..277a260 100644
> --- a/include/uapi/linux/if_tun.h
> +++ b/include/uapi/linux/if_tun.h
> @@ -22,21 +22,11 @@
>  
>  /* Read queue size */
>  #define TUN_READQ_SIZE	500
> -
> -/* TUN device flags */
> -#define TUN_TUN_DEV 	0x0001	
> -#define TUN_TAP_DEV	0x0002
> +/* TUN device type flags: deprecated. Use IFF_TUN/IFF_TAP instead. */
> +#define TUN_TUN_DEV 	IFF_TUN
> +#define TUN_TAP_DEV	IFF_TAP
>  #define TUN_TYPE_MASK   0x000f
>  
> -#define TUN_FASYNC	0x0010
> -#define TUN_NOCHECKSUM	0x0020
> -#define TUN_NO_PI	0x0040
> -/* This flag has no real effect */
> -#define TUN_ONE_QUEUE	0x0080
> -#define TUN_PERSIST 	0x0100	
> -#define TUN_VNET_HDR 	0x0200
> -#define TUN_TAP_MQ      0x0400
> -
>  /* Ioctl defines */
>  #define TUNSETNOCSUM  _IOW('T', 200, int) 
>  #define TUNSETDEBUG   _IOW('T', 201, int) 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 9dd3746..bc89d07 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -103,6 +103,21 @@ do {								\
>  } while (0)
>  #endif
>  
> +/* TUN device flags */
> +
> +/* IFF_ATTACH_QUEUE is never stored in device flags,
> + * overload it to mean fasync when stored there.
> + */
> +#define TUN_FASYNC	IFF_ATTACH_QUEUE
> +#define TUN_NO_PI	IFF_NO_PI
> +/* This flag has no real effect */
> +#define TUN_ONE_QUEUE	IFF_ONE_QUEUE
> +#define TUN_PERSIST 	IFF_PERSIST
> +#define TUN_VNET_HDR 	IFF_VNET_HDR
> +#define TUN_TAP_MQ      IFF_MULTI_QUEUE
> +
> +#define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
> +		      IFF_MULTI_QUEUE)
>  #define GOODCOPY_LEN 128
>  
>  #define FLT_EXACT_COUNT 8
> @@ -1521,32 +1536,7 @@ static struct proto tun_proto = {
>  
>  static int tun_flags(struct tun_struct *tun)
>  {
> -	int flags = 0;
> -
> -	if (tun->flags & TUN_TUN_DEV)
> -		flags |= IFF_TUN;
> -	else
> -		flags |= IFF_TAP;
> -
> -	if (tun->flags & TUN_NO_PI)
> -		flags |= IFF_NO_PI;
> -
> -	/* This flag has no real effect.  We track the value for backwards
> -	 * compatibility.
> -	 */
> -	if (tun->flags & TUN_ONE_QUEUE)
> -		flags |= IFF_ONE_QUEUE;
> -
> -	if (tun->flags & TUN_VNET_HDR)
> -		flags |= IFF_VNET_HDR;
> -
> -	if (tun->flags & TUN_TAP_MQ)
> -		flags |= IFF_MULTI_QUEUE;
> -
> -	if (tun->flags & TUN_PERSIST)
> -		flags |= IFF_PERSIST;
> -
> -	return flags;
> +	return tun->flags & (TUN_FEATURES | IFF_PERSIST | IFF_TUN | 
> IFF_TAP);
>  }
>  
>  static ssize_t tun_show_flags(struct device *dev, struct 
> device_attribute *attr,
> @@ -1706,28 +1696,8 @@ static int tun_set_iff(struct net *net, struct 
> file *file, struct ifreq *ifr)
>  
>  	tun_debug(KERN_INFO, tun, "tun_set_iff\n");
>  
> -	if (ifr->ifr_flags & IFF_NO_PI)
> -		tun->flags |= TUN_NO_PI;
> -	else
> -		tun->flags &= ~TUN_NO_PI;
> -
> -	/* This flag has no real effect.  We track the value for backwards
> -	 * compatibility.
> -	 */
> -	if (ifr->ifr_flags & IFF_ONE_QUEUE)
> -		tun->flags |= TUN_ONE_QUEUE;
> -	else
> -		tun->flags &= ~TUN_ONE_QUEUE;
> -
> -	if (ifr->ifr_flags & IFF_VNET_HDR)
> -		tun->flags |= TUN_VNET_HDR;
> -	else
> -		tun->flags &= ~TUN_VNET_HDR;
> -
> -	if (ifr->ifr_flags & IFF_MULTI_QUEUE)
> -		tun->flags |= TUN_TAP_MQ;
> -	else
> -		tun->flags &= ~TUN_TAP_MQ;
> +	tun->flags = (tun->flags & ~TUN_FEATURES) |
> +		(ifr->ifr_flags & TUN_FEATURES);
>  
>  	/* Make sure persistent devices do not get stuck in
>  	 * xoff state.
> @@ -1890,9 +1860,11 @@ static long __tun_chr_ioctl(struct file *file, 
> unsigned int cmd,
>  	if (cmd == TUNGETFEATURES) {
>  		/* Currently this just means: "what IFF flags are valid?".
>  		 * This is needed because we never checked for invalid flags on
> -		 * TUNSETIFF. */
> -		return put_user(IFF_TUN | IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE |
> -				IFF_VNET_HDR | IFF_MULTI_QUEUE,
> +		 * TUNSETIFF.  Why do we report IFF_TUN and IFF_TAP which are
> +		 * not legal for TUNSETIFF here?  It's probably a bug, but it
> +		 * doesn't seem to be worth fixing.
> +		 */

The question is not very clear. IFF_TUN and IFF_TAP are legal for 
 ifr.ifr_flags during TUNSETIFF. No?
> 
> +		return put_user(IFF_TUN | IFF_TAP | TUN_FEATURES,
>  				(unsigned int __user*)argp);
>  	} else if (cmd == TUNSETQUEUE)
>  		return tun_set_queue(file, &ifr);
> -- 
> MST
> 
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