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From: Paul Brook <paul@codesourcery.com>
Date: Wed, 7 Apr 2010 23:58:53 +0100
References: <1270674156-9345-1-git-send-email-amit.shah@redhat.com>
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Message-Id: <201004072358.53971.paul@codesourcery.com>
Subject: [Qemu-devel] Re: [PATCH 0/8] (v2) chardev,
	virtio-console: flow control, error handling, fixes
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To: Amit Shah <amit.shah@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, qemu list <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

> Hello,
> 
> This patchset introduces flow control to virtio-console and
> chardev-based virtio serial ports. This series is based on the
> previous series I sent on Mar 31st (00/17: v4: virtio-serial fixes,
> new abi for port discovery)
> 
> The qemu chardevs can now return -EAGAIN when a non-blocking remote
> isn't ready to accept more data.
> 
> Comments?

This is a major change in semantics. Are you sure all users handle this 
correctly? My guess is that most of the devices don't.
EAGAIN isn't really a useful response unless you have some way of notifying 
the device that it can send more data.

Paul