netdev - Re: [PATCH net-next] sysfs: add entry to indicate network interfaces with random MAC address

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Date:	Tue, 20 Jul 2010 12:20:44 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Stefan Assmann <sassmann@...hat.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	davem@...emloft.net, Andy Gospodarek <gospo@...hat.com>,
	"Rose, Gregory V" <gregory.v.rose@...el.com>,
	"Duyck, Alexander H" <alexander.h.duyck@...el.com>,
	Casey Leedom <leedom@...lsio.com>,
	Harald Hoyer <harald@...hat.com>
Subject: Re: [PATCH net-next] sysfs: add entry to indicate network
 interfaces with random MAC address

On Tue, 2010-07-20 at 12:50 +0200, Stefan Assmann wrote:
> From: Stefan Assmann <sassmann@...hat.com>
> 
> Reserve a bit in struct net_device to indicate whether an interface
> generates its MAC address randomly, and expose the information via
> sysfs.
> May look like this:
> /sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/net/eth0/ifrndmac
> 
> By default the value of ifrndmac is 0. Any driver that generates the MAC
> address randomly should return a value to 1.

The name should incorporate 'address', not 'mac', for consistency with
the generic 'address' attribute.

What about devices that 'steal' MAC addresses from slave devices?
Currently I believe udev has special cases for them but ideally these
drivers would indicate explicitly that their addresses are not stable
identifiers (even though they aren't random).

[...]
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index b626289..2ea0298 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -845,6 +845,7 @@ struct net_device {
>  #define NETIF_F_FCOE_MTU	(1 << 26) /* Supports max FCoE MTU, 2158 bytes*/
>  #define NETIF_F_NTUPLE		(1 << 27) /* N-tuple filters supported */
>  #define NETIF_F_RXHASH		(1 << 28) /* Receive hashing offload */
> +#define NETIF_F_RNDMAC		(1 << 29) /* Interface with random MAC address */
[...]

This is not really a feature, and we are running out of real feature
bits.  Can you find somewhere else to put this flag?

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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