On Mon, Feb 13, 2017 at 08:36:45AM +0100, Thomas Huth wrote: > On 13.02.2017 06:33, David Gibson wrote: > > On Tue, Nov 22, 2016 at 10:19:38AM +1100, Sam Bobroff wrote: > >> The spapr-vlan device in QEMU has always presented it's MAC address in > >> the device tree as an 8 byte value, even though PAPR requires it to be > >> 6 bytes. This is because, at the time, AIX required the value to be 8 > >> bytes. However, modern versions of AIX support the (correct) 6 > >> byte value so they no longer require the workaround. > >> > >> It would be neatest to always provide a 6 byte value but that would > >> cause a problem with old Linux kernel ibmveth drivers, so the old 8 > >> byte value is still presented when necessary. > >> > >> Since commit 13f85203e (3.10, May 2013) the driver has been able to > >> handle 6 or 8 byte addresses so versions after that don't need to be > >> considered specially. > >> > >> Drivers from kernels before that can also handle either type of > >> address, but not always: > >> * If the first byte's lowest bits are 10, the address must be 6 bytes. > >> * Otherwise, the address must be 8 bytes. > >> (The two bits in question are significant in a MAC address: they > >> indicate a locally-administered unicast address.) > >> > >> So to maintain compatibility the old 8 byte value is presented when > >> the lowest two bits of the first byte are not 10. > >> > >> Signed-off-by: Sam Bobroff <sam.bobr...@au1.ibm.com> > > > > Sorry, I didn't see this one until now. > > > > Since we need a workaround for the workaround, is it actually worth > > going to the 6-byte property? > > 8-byte addresses are just wrong, all other network devices and the > standard use 6-byte MAC addresses instead. So we should use 6-byte > addresses in QEMU whenever it is possible, too. Unfortunately there are > still guests in the field that use this bad assumption with 8 byte > addresses, so I think this work-around is the best we can and should do > right now.
Hm, yes, good point. Applied to ppc-for-2.9.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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