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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH v3 2/4] char: Add ability to provide a
	callback when write won't return -EAGAIN
Date: Tue, 20 Apr 2010 13:28:48 +0100
References: <1271319378-9811-1-git-send-email-amit.shah@redhat.com>
	<4BCD90C2.7050009@redhat.com>
	<20100420114420.GA20123@amit-x200.redhat.com>
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To: Amit Shah <amit.shah@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, qemu list <qemu-devel@nongnu.org>

> I sent out this series as a "feeler" to see if the approach was
> acceptable.
> 
> Paul didn't reply to my reply addressing his concern, so I take that as
> he's OK with the approach as well :-)

I'd probably exposed this as an asyncronous write rather than nonblocking 
operation. However both have their issues and I guess for character devices 
your approach makes sense (c.f. block devices where we want concurrent 
transfers).

It would be useful to have a debugging mode where the chardev layer 
deliberately returns spurious EAGAIN and short writes. Otherwise you've got a 
lot of very poorly tested device fallback code. I have low confidence in 
getting this right first time :-)

Paul