Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle terminating signals.

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Anthony Liguori writes ("Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle 
terminating signals."):
> Then you need a pipe per-signal and you can't accurately simulate 
> threadfd() (since you can't communicate siginfo).

No, you don't need a pipe per signal.  You only need multiple pipes if
you have multiple different event loops which are each capable of
handling only a subset of the signals, _and_ you're unwilling to use
an atomic flag variable (eg, cpu_interrupt) or its equivalent.

But we already have cpu_interrupt, and of course the aio completion
system has its own recording of what's going on.  So that does not
apply to qemu.

All that's needed is a reliable, race-free, way of avoiding spuriously
blocking in a syscall when an event occurs between checking the state
variables (aio_error, cpu interrupt check) and the call to select().
One fd is sufficient for that.

Just to make that concrete, even if we extended my patch to use its
mechanism for SIGINT et al I don't think a second pipe would be
needed.

> I don't see threads as a problem.  Are you concerned about mini-OS?

Minios certainly doesn't currently have any threads and it would
probably be a severe pain to introduce them.  That's just one example
of a portability problem.

Ian.

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