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Date: Fri, 05 Apr 2013 15:01:20 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] qemu-char: eliminate busy waiting on
 can_read returning zero
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: amit.shah@redhat.com, peter.crosthwaite@xilinx.com, qemu-devel@nongnu.org, gson@gson.org

Il 05/04/2013 14:54, Anthony Liguori ha scritto:
> I guess this works with migration because we assume that after migration
> the main loop will do a complete run?

Yes, migration will terminate in an fd handler, and the next round of
the main loop will re-evaluate chr_read.

> Is this a safe assumption or does
> there need to be a qemu_notify_event() somewhere after migration to make
> sure this doesn't cause a hang?

There could be a qemu_chr_accept_input() for all character devices after
migration.  I think that would be a separate patch.

Regarding the need or not for Peter's patch: the patch might be needed
this kind of busy-wait fix was required often.  As far as I recall, this
is the first we ever had, and it came after an almost-complete rewrite.
 It seems rare enough, that it's much better to fix the root causes when
they appear---not the symptoms.

Paolo