netdev - Re: [patch net-next 1/4] net: introduce new priv_flag indicating iface capable of change mac when running

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Date:	Thu, 28 Jun 2012 17:24:52 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, rusty@...tcorp.com.au,
	mst@...hat.com, virtualization@...ts.linux-foundation.org,
	edumazet@...gle.com, danny.kukawka@...ect.de,
	shimoda.hiroaki@...il.com
Subject: Re: [patch net-next 1/4] net: introduce new priv_flag indicating
 iface capable of change mac when running

On Thu, 2012-06-28 at 16:10 +0200, Jiri Pirko wrote:
> Introduce IFF_LIFE_ADDR_CHANGE priv_flag and use it to disable
> netif_running() check in eth_mac_addr()
> 
> Signed-off-by: Jiri Pirko <jpirko@...hat.com>
> ---
>  include/linux/if.h |    2 ++
>  net/ethernet/eth.c |    2 +-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/if.h b/include/linux/if.h
> index f995c66..fd9ee7c 100644
> --- a/include/linux/if.h
> +++ b/include/linux/if.h
> @@ -81,6 +81,8 @@
>  #define IFF_UNICAST_FLT	0x20000		/* Supports unicast filtering	*/
>  #define IFF_TEAM_PORT	0x40000		/* device used as team port */
>  #define IFF_SUPP_NOFCS	0x80000		/* device supports sending custom FCS */
> +#define IFF_LIFE_ADDR_CHANGE 0x100000	/* device supports hardware address
> +					 * change when it's running */
>  
> 
>  #define IF_GET_IFACE	0x0001		/* for querying only */
> diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
> index 36e5880..8f8ded4 100644
> --- a/net/ethernet/eth.c
> +++ b/net/ethernet/eth.c
> @@ -283,7 +283,7 @@ int eth_mac_addr(struct net_device *dev, void *p)
>  {
>  	struct sockaddr *addr = p;
>  
> -	if (netif_running(dev))
> +	if (!(dev->priv_flags & IFF_LIFE_ADDR_CHANGE) && netif_running(dev))
>  		return -EBUSY;
>  	if (!is_valid_ether_addr(addr->sa_data))
>  		return -EADDRNOTAVAIL;

Since the memcpy() is not atomic, there is a small window where a reader
could get a half-changed mac address. I guess its a detail.



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