netdev - RE: [PATCH net-next 1/1] skbuff: Extend gso

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Date:   Fri, 7 Apr 2017 13:36:05 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Steffen Klassert' <steffen.klassert@...unet.com>,
        David Miller <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next 1/1] skbuff: Extend gso_type to unsigned int.

From: Steffen Klassert
> Sent: 03 April 2017 09:16
> All available gso_type flags are currently in use, so
> extend gso_type from 'unsigned short' to 'unsigned int'
> to be able to add further flags.
> 
> We also reorder the struct skb_shared_info to use
> two bytes of the four byte hole before dataref.
> All fields before _unused are cleared now, i.e.
> two bytes more than before the change.
...
> -	 * Warning : all fields before dataref are cleared in __alloc_skb()
> +	 * Warning : all fields before _unused are cleared in __alloc_skb()
>  	 */
> +	unsigned short	_unused;
>  	atomic_t	dataref;
> 
>  	/* Intermediate layers must ensure that destructor_arg
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 9f78109..8796b93 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -257,7 +257,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
> 
>  	/* make sure we initialize shinfo sequentially */
>  	shinfo = skb_shinfo(skb);
> -	memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
> +	memset(shinfo, 0, offsetof(struct skb_shared_info, _unused));
>  	atomic_set(&shinfo->dataref, 1);
>  	kmemcheck_annotate_variable(shinfo->destructor_arg);

Is it worth adding a specific field name for the end of the 'zero' area?
Either as a #define or anonymous union.

I think that changing the definition to:
	union {
		unsigned short	_unused;
		atomic_t	dataref;
	};
would require no other changes.

	David