From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36522) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a1trl-0000wq-LB for qemu-devel@nongnu.org; Thu, 26 Nov 2015 05:33:30 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a1tri-0000hH-BX for qemu-devel@nongnu.org; Thu, 26 Nov 2015 05:33:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40597) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a1tri-0000h2-5p for qemu-devel@nongnu.org; Thu, 26 Nov 2015 05:33:26 -0500 Date: Thu, 26 Nov 2015 12:33:22 +0200 From: "Michael S. Tsirkin" Message-ID: <20151126121944-mutt-send-email-mst@redhat.com> References: <1441753806-14225-1-git-send-email-marcandre.lureau@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1441753806-14225-1-git-send-email-marcandre.lureau@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH RFC 00/14] vhost-user: shutdown and reconnection List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: marcandre.lureau@redhat.com Cc: mukawa@igel.co.jp, qemu-devel@nongnu.org On Wed, Sep 09, 2015 at 01:09:52AM +0200, marcandre.lureau@redhat.com wro= te: > From: Marc-Andr=E9 Lureau >=20 > In a previous series "Add feature to start QEMU without vhost-user > backend", Tetsuya Mukawa proposed to allow the vhost-user backend to > disconnect and reconnect. However, Michael Tsirkin pointed out that > you can't do that without extra care, because the guest and hypervisor > don't know the slave ring manipulation state, there might be pending > replies for example that could be lost, and suggested to reset the > guest queues, but this requires kernel changes, and it may have to > clear the ring and lose queued packets. >=20 > The following series starts from the idea that the slave can request a > "managed" shutdown instead and later recover (I guess the use case for > this is to allow for example to update static dispatching/filter rules > etc) I'm still not sure users actually need this. I am inclined to think we should teach guests to respond to NEED_RESET status. Then to handle disconnect, we would - deactivate the disconnected backend - stop VM, and wait for a reconnect - set NEED_RESET status, and re-activate the backend after guest reset --=20 MST