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    SubjectRe: [PATCH net-next] sysfs: add entry to indicate network interfaces with random MAC address
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    On Tue, 2010-07-20 at 13:47 +0200, Stefan Assmann wrote:
    > On 20.07.2010 13:20, Ben Hutchings wrote:
    > > On Tue, 2010-07-20 at 12:50 +0200, Stefan Assmann wrote:
    > >> From: Stefan Assmann <sassmann@redhat.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.
    >
    > We can call it "ifrndhwaddr" if that's more consistent.
    >
    > >
    > > 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).
    >
    > It's really up to the driver to decide whether it makes sense to set the
    > flag or not. The question is what should udev do with these MAC address
    > stealing devices apart from ignoring them? Sorry I have no higher
    > insight into it.
    > This flag has the purpose to allow udev to explicitly handle devices
    > that generate their MAC address randomly and generate a persistent
    > rule based on the device path instead of the MAC address.
    > I'm open for suggestions but I'm not sure we can handle both cases with
    > a single flag.

    OK, then call it something like 'address_temporary'.

    > JFYI this is an alternative approach to changing the kernel name of VFs
    > to vfeth. The advantage of this way should be that we don't break any
    > user-space applications that rely on network interfaces being names
    > "ethX". Actually this goes in the direction of "fixing udev" which was
    > what you asked for in your comment on my first patch concering vfeth. :)
    >
    > >
    > > [...]
    > >> 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?
    >
    > Actually Dave Miller suggested to put it there. What other place is
    > there to put it?

    If Dave said that then I'm sure it's OK.

    However, if you define this as an interface flag (net_device::flags;
    <linux/if.h>) and add it to the set of changeable flags in
    __dev_change_flags(), user-space will be able to clear the flag if it
    later sets a stable address.

    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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