From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dor Laor Subject: Re: KVM call agenda for Apr 27 Date: Tue, 27 Apr 2010 12:08:37 +0300 Message-ID: <4BD6A995.2010006@redhat.com> References: <20100426172634.GC15278@x200.localdomain> <4BD5D28C.7080700@codemonkey.ws> <20100426221258.GH15278@x200.localdomain> <4BD61584.9080208@codemonkey.ws> <4BD69D03.2050502@redhat.com> <4BD6A4CA.6070306@redhat.com> <4BD6A6BA.1090600@redhat.com> Reply-To: dlaor@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , Chris Wright , kvm@vger.kernel.org, qemu-devel@nongnu.org, Kevin Wolf To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:27558 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753876Ab0D0JHL (ORCPT ); Tue, 27 Apr 2010 05:07:11 -0400 In-Reply-To: <4BD6A6BA.1090600@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 04/27/2010 11:56 AM, Avi Kivity wrote: > On 04/27/2010 11:48 AM, Dor Laor wrote: >>> Here's another option: an nbd-like protocol that remotes all BlockDriver >>> operations except read and write over a unix domain socket. The open >>> operation returns an fd (SCM_RIGHTS strikes again) that is used for read >>> and write. This can be used to implement snapshots over LVM, for >>> example. >>> >> >> >> Why w/o read/writes? > > To avoid the copying. Of course, just pass the offset+len on read/write too > >> the watermark code needs them too (as info, not the actual buffer). > > Yeah. It works for lvm snapshots, not for watermarks. > >> >> IMHO the whole thing is way over engineered: >> a) Having another channel into qemu is complicating management >> software. Isn't the monitor should be the channel? Otherwise we'll >> need to create another QMP (or nbd like Avi suggest) for these >> actions. It's extra work for mgmt and they will have hard time to >> understand events interleaving of the various channels > > block layer plugins allow intercepting all interesting block layer > events, not just write-past-a-watermark, and allow actions based on > those events. It's a more general solution. No problem there, as long as we do try to use the single existing QMP with the plugins. Otherwise we'll create QMP2 for the block events in a year from now. > >> b) How the plugins are defined? Is it scripts? Binaries? Do they open >> their own sockets? > > Shared objects. > >