linux-kernel - Re: [PATCH] virtio_console: Add support for multiple ports for generic guest and host communication

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Message-ID: <20090917165701.400ad28c@lxorguk.ukuu.org.uk>
Date:	Thu, 17 Sep 2009 16:57:01 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	Markus Armbruster <armbru@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, greg@...ah.com
Subject: Re: [PATCH] virtio_console: Add support for multiple ports for
 generic guest and host communication

> Alan, I'm not sure how many ports at a time people would want to use so
> allocating one major device for this seems OK?

We have very large minor number ranges now so one dynamic major should do
you for a while yet. Probably forever but thats always asking for a
"640K.." moment ;)


> +static ssize_t fill_readbuf(struct virtio_console_port *port,
> +			    char *out_buf, size_t out_count, bool to_user)
> +{

Save yourself serious grief - and the FIXME pain noted below - unless you
are shipping huge objects use a bounce buffer and kill off the to_user
stuff - modern CPUs are so fast doing cache transfers it really isn't
worth the suffering for small stuff.

> +			ret = copy_to_user(out_buf + out_offset,
> +					   buf->buf + buf->offset,
> +					   copy_size);
> +			/* FIXME: Deal with ret != 0 */
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