While trying to fix a bug in the s390 migration code, I noticed that QEMU ignores practically all errors returned from that VM ioctl. QEMU behaves as specified in the KVM api and only processes -1 (-EPERM) as an error.
Unfortunately the documentation is wrong/old and KVM may return -EFAULT, -EINVAL, -ENOTSUPP (BookE) and -ENOENT. This bugs me, as I found a case where I want to return -EFAULT because of guest memory problems and QEMU will still happily migrate the VM. I currently don't see a reason why we continue to migrate on EFAULT and EINVAL. But returning -error from kvm_physical_sync_dirty_bitmap might also a bit hard, as it kills QEMU. Do we want to fix this and if, how do we want it done? If not we at least have a definitive mail to point to when the next one comes around. I also have a KVM patch to update the api documentation if wanted (maybe we should dust that off a bit anyhow). This has been brought up in 2009 [1] the first time and was more or less fixed and then reverted in 2014 [2]. The reason in [1] was that PPC hadn't settled yet on a valid return code. In [2] it was too close to the v2 to handle it properly. [1] https://lists.nongnu.org/archive/html/qemu-devel/2009-07/msg01772.html [2] https://lists.nongnu.org/archive/html/qemu-devel/2014-04/msg01993.html Cheers, Janosch
