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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 28 Jun 2012 23:32:34 +0300

On Thu, Jun 28, 2012 at 05:24:52PM +0200, Eric Dumazet wrote:
> 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 <[email-masked]>
> > ---
> >  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.
> 

At least for virtio nothing changes - we had this bug forever.
How'd you fix this?

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MST