Re: [PATCH] fix tuntap oversight

[Jeff Garzik <jgarzik@pobox.com>]

Jeremy Martin wrote:
> On Mon, Apr 12, 2004 at 12:15:51AM -0700, David S. Miller wrote:
> 
>>This netif_running() check is not necessary, and in fact
>>wrong.
>>
>>In fact, if ethernet drivers erroneously do this, this causes
>>them to fail to support the ALB bonding driver modes which
>>require on-the-fly MAC address changes while the interface is
>>up.
>>
> 
> 
> I just took a look in drivers/net/
> and 
> 	acenic.c
> 	atarilance.c
> 	b44.c
> 	cs89x0.c
> 	net_init.c
> 	typhoon.c
> 
> all use that netif_running() check when setting the MAC.  I actually just pulled
> the function from net_init.c for the tun change.  Are these broken?
> (I'm asking in total ignorance so be gentle :).

It's different for a driver that drives real hardware.

struct net_device::set_mac_address() is called inside rtnl_lock().  The 
safe thing to do is
1) read MAC address from eeprom on probe
2) write MAC address to hardware upon each dev->open()
3) use default eth_mac_addr() from net_init.c

And the netif_running() check in eth_mac_addr() is correct, because it 
does not update the hardware MAC address (which in this API would be 
impossible).

Normally the netif_running() check is for hardware that cannot update 
its MAC address safely during operation.

	Jeff