From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1ME5rB-0003uR-CK for qemu-devel@nongnu.org; Tue, 09 Jun 2009 14:15:33 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1ME5r6-0003s9-G6 for qemu-devel@nongnu.org; Tue, 09 Jun 2009 14:15:32 -0400 Received: from [199.232.76.173] (port=42041 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1ME5r5-0003rq-VK for qemu-devel@nongnu.org; Tue, 09 Jun 2009 14:15:28 -0400 Received: from mx2.redhat.com ([66.187.237.31]:58555) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1ME5r5-0004Y3-JH for qemu-devel@nongnu.org; Tue, 09 Jun 2009 14:15:27 -0400 Date: Tue, 9 Jun 2009 19:15:22 +0100 From: "Richard W.M. Jones" Subject: Re: [Qemu-devel] Re: [PATCH] virtio-serial: PCI device for simple host <-> guest communication Message-ID: <20090609181522.GA11485@amd.home.annexia.org> References: <1244565768-9103-1-git-send-email-amit.shah@redhat.com> <1244565768-9103-2-git-send-email-amit.shah@redhat.com> <1244565768-9103-3-git-send-email-amit.shah@redhat.com> <1244565768-9103-4-git-send-email-amit.shah@redhat.com> <4A2E98AD.2090904@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A2E98AD.2090904@siemens.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Amit Shah , qemu-devel@nongnu.org On Tue, Jun 09, 2009 at 07:15:25PM +0200, Jan Kiszka wrote: > Amit Shah wrote: > > This interface presents a char device from which bits can be > > sent and read. > > > > Sample uses for such a device can be obtaining info from the > > guest like the file systems used, apps installed, etc. for > > offline usage and logged-in users, clipboard copy-paste, etc. > > for online usage. > > Out of curiosity: What is the advantage over instantiating a multiport > 16550A PCI card? Will those channels be so performance critical? 16550A has a couple of problems: The fixed sized FIFO (16 bytes) can cause problems if you send data too quickly. (I've seen this problem when sending too much data from host to the guest, but I can't find the bug report right now ...). Secondly UARTs are complicated to emulate compared to a clean virtio device. Would we be happy with the address space taken up and amount of emulation going on once we had, say, 16 emulated ports? On the other hand, multiport cards don't require special drivers in the guest ... Rich. -- Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones Read my programming blog: http://rwmj.wordpress.com Fedora now supports 75 OCaml packages (the OPEN alternative to F#) http://cocan.org/getting_started_with_ocaml_on_red_hat_and_fedora