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From: Paul Brook <paul@codesourcery.com>
Date: Wed, 5 May 2010 14:34:19 +0100
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Subject: [Qemu-devel] Re: [PATCH v7 4/6] char: Add qemu_chr_write_nb() for
	nonblocking writes
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Amit Shah <amit.shah@redhat.com>, Juan Quintela <quintela@redhat.com>, qemu list <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

> I really dislike the idea of adding another function for this.  Can you
> explain why you need this functionality for virtio-console and why this
> functionality isn't needed for everything else?

This functionality should (in principle) be used by all serial port 
implementations.

Physical serial ports are sufficiently crufty and low-performance that noone 
actually uses them nowadays.  I expect that the only significant real-world 
use is for serial consoles, which never send enough data to care that writes 
stall the whole machine.

With virtio-serial we've made serial ports a viable solution to a whole range 
of problems.  It's likely that applications that may send nontrivial amounts 
of data, or clients will not be ready to process the data immediately.

Paul