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Re: [PATCH] hw/char/pl011: Output characters using best-effort mode

From: Gavin Shan
Subject: Re: [PATCH] hw/char/pl011: Output characters using best-effort mode
Date: Mon, 24 Feb 2020 10:45:26 +1100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0

On 2/22/20 5:15 AM, Paolo Bonzini wrote:
On 21/02/20 14:14, Peter Maydell wrote:
The initial case reported by Gavin in this thread is
"-serial tcp:" with the other end being a program which
listens on TCP port 50900 and then sleeps without accepting any incoming
connections, which blocks the serial port output and effectively blocks
the guest bootup. If you want to insulate the guest from badly
behaved consumers like that (or the related consumer who accepts
the connection and then just doesn't read data from it) you probably
need to deal with more than just POLLHUP. But I'm not sure how much
we should care about these cases as opposed to just telling users
not to do that...

No, I think we don't do anything (on purpose; that is, it was considered
the lesser evil) for x86 in that case.

Paolo and Peter, thanks for your time on the discussion. So I think the
conclusion is we don't do anything for pl011 either? :)

Actually, the issue was reported by libvirt developer. A VM is started
with serial on tcp socket, which is never accepted on server side. It
practically blocks the VM to boot up. I will tell the libvirt developer
to hack their code to avoid the race if we don't do anything in qemu.


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