From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC 1/4] New virtio bus driver Date: Mon, 9 Jul 2007 13:18:47 +0200 Message-ID: <200707091318.48261.arnd@arndb.de> References: <20070706124200.988637662@arndb.de> <200707082229.00810.arnd@arndb.de> <4691DA69.4060204@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <4691DA69.4060204@qumranet.com> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Avi Kivity Cc: virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Monday 09 July 2007, Avi Kivity wrote: > > That is much harder to do, it would require a separate interrupt if y= ou > > want to have a device independent mechanism. Most real buses (like PC= I) > > don't have this, so I'm not sure it's good to do this at the virtio > > layer. You already listed the media change notification, which can > > be handled without this by either removing and adding the complete > > virtio device, or by using a channel for out-of-band data like scsi. >=20 > At the very least, we need an interrupt for device hotplug. =A0That sam= e > interrupt can be used to notify the guest about configuration changes > within a device ("rescan the virtbus and all who sail in her"). There is an important difference between device reconfiguration and bus reconfiguration (device hotplug). If we want device reconfiguration, that needs to be implemented within the virtio layer, because the device drivers need to know about it. For hotplugging devices, we need to have a bus specific mechanism, while the device drivers only care about 'new device found' and 'device is gone' events that are already supported by any linux bus_type. The problem with hotplugging devices on PCI is that there is not a good standard for this yet. The best option we have is probably PCI express hotplug, but I'm not sure how many legacy operating systems already suppo= rt this. Arnd <><