On 01/19/2010 03:25 PM, Jan Kiszka wrote:
For kvm-kmod, I'm fighting with compat support for eventfd_ctx_remove_wait_queue. I basically have a solution for kernels with CONFIG_KPROBES enabled (I need to look up unexported __wake_up_locked[_key]), but there will also be target kernels that do not have this. So there are three options for that case: - Warn the user and fall back to the old racy approach - (Somehow) disable KVM subsystems that use eventfd - Refuse to start KVM As far as I understood, irqfd is interesting for device assignment and now also for vhost, right? What about ioeventfd? I just wonder how broad the impact of a broken or non-existent eventfd subsystem for kvm-kmod is. Any thoughts welcome.
Since vhost is only a performance option (and there isn't a vhost-kmod) and device assignment wants a new kernel anyway (and only applies to a small subset of users), I think it's okay to drop it from kvm-kmod. It should be sufficient to return 0 from KVM_CHECK_EXCEPTION and substitute some stubs for the functions.
ioeventfd/irqfd are useful for inter-guest wakeups, but there isn't any public code for that that I'm aware of.
PS: If anyone forgot why Avi handed over this job, you should now remember why. :)
It's only going to get more difficult, I'm afraid. The list of old kernels keeps growing and we're going to depend on core kernel functionality more and more.
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