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Date: Wed, 30 Jul 2014 12:52:41 -0600
From: Chris Friesen <chris.friesen@windriver.com>
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Subject: [Qemu-devel] questions about host side of virtio-serial
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To: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Amit Shah <amit.shah@redhat.com>

Hi,

I'm working on a native user of virtio-serial (ie, not going via the 
qemu guest agent).

The information at "http://www.linux-kvm.org/page/Virtio-serial_API" 
does a good job of describing the guest side of things, but has very 
little information about the host side of things.

In particular, assuming that the host side is using a chardev mapped to 
a unix socket:

1) Is there any way for the host app to get information about whether or 
not the guest is reading the messages?  (i.e. logically equivalent to 
getting POLLHUP in the guest when the host app disconnects.)

2) Suppose the host sends a large message.  The guest app reads a 
portion of the message, then crashes.  We respawn the guest app and 
start reading again, but now we're in the middle of a message of 
arbitrary size.  Is there a recommended technique to re-sync the host 
and guest?

3) Same as 2, but the guest sending to the host and the host app 
crashing partway through.

4) If nothing in the guest is reading the data, how much data can the 
host send before it will get an error?  Is there a way to adjust this?

Thanks,
Chris