On 09/04/2012 01:06 PM, Paolo Bonzini wrote: > Il 04/09/2012 11:51, Jan Kiszka ha scritto: >>> > >>> > I don't mean to say we shouldn't care about them, but there are likely >>> > to be a lot more users doing backwards migration than users running >>> > those guests, let alone migrating them (forwards or backwards). The >>> > pragmatic choice is clear. >> BTW, did anyone actually test backward migration recently? I thought to >> remember I effectively broke it in 1.1 with some changes to the i8259 >> (or was it the PIT?) vmstate, and no one really cared about this or my >> first proposals to fix it. > > Correct: commit ce967e2 (i8254: Rework & fix interaction with HPET in > legacy mode, 2012-02-01) bumped the PIT version from 2 to 3.
Gah, this is 1.1, so there's no way to fix it. > RTC > changes will break it more in 1.3. > > Honestly, backwards migration only works on "enterprise" qemu-kvm > because it is tested only there. And so far the only sample across > major releases is that RHEL6->RHEL5 migration didn't work. I expect that we will want 7->6, though we may have to settle for minor releases only. > Here the choice is between changing guest behavior by defaulting to 4/2, > and always transmitting the subsection by defaulting to 0/0. The latter > makes the subsection useless, so at that point we might as well bump the > version number and board said flight to the Pacific. So we do the 4/2 thing. I expect if we go they'll tell us they don't do backwards flights. -- error compiling committee.c: too many arguments to function
