[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [XEN PATCH 1/7] xen: introduce XENFEAT_xenstore_late_init
On Mon, 10 Jan 2022, Jan Beulich wrote: > On 08.01.2022 01:49, Stefano Stabellini wrote: > > Introduce a new feature flag to signal that xenstore will not be > > immediately available at boot time. Instead, xenstore will become > > available later, and a notification of xenstore readiness will be > > signalled to the guest using the xenstore event channel. > > In addition to what Julien has said, I'd like to point out that Linux'es > xenbus driver already has means to deal with xenstored not being around > right away (perhaps because of living in a stubdom which starts in > parallel). I therefore wonder whether what you want can't be achieved > entirely inside that driver, without any new feature flag. The fewer changes to Linux the better but we couldn't find a way to make it work with zero changes. In a way, the patch for Linux is re-using the existing infrastructure to delay initialization, e.g. xenbus_probe_thread to call xenbus_probe later. However, today there is nothing stopping Linux/HVM to continue initialization immediately except for xs_hvm_defer_init_for_callback which is not applicable in this case. So we introduced XENFEAT_xenstore_late_init. As I wrote in another reply, I think we could do without XENFEAT_xenstore_late_init if we instead rely on checking for HVM_PARAM_STORE_EVTCHN being valid and HVM_PARAM_STORE_PFN being zero. But either way as far as I can tell we need to add a new check to delay xenstore initialization in Linux/HVM.
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