Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758414Ab2BMXdq (ORCPT ); Mon, 13 Feb 2012 18:33:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:3951 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758333Ab2BMXdn (ORCPT ); Mon, 13 Feb 2012 18:33:43 -0500 Date: Tue, 14 Feb 2012 01:33:35 +0200 From: "Michael S. Tsirkin" To: ronnie sahlberg Cc: Hannes Reinecke , Dor Laor , "Nicholas A. Bellinger" , Christian Borntraeger , James Bottomley , Paolo Bonzini , Christian Hoff , borntrae@linux.vnet.ibm.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, rusty@rustcorp.com.au, Stefan Hajnoczi , target-devel Subject: Re: Pe: [PATCH v5 1/3] virtio-scsi: first version Message-ID: <20120213233334.GC4430@redhat.com> References: <1329136806.9333.383.camel@haakon2.linux-iscsi.org> <4F3907EB.4030402@redhat.com> <20120213130005.GB26773@redhat.com> <20120213131848.GD26773@redhat.com> <4F39287A.9030808@suse.de> <20120213225623.GA2988@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4072 Lines: 94 On Tue, Feb 14, 2012 at 10:30:59AM +1100, ronnie sahlberg wrote: > On Tue, Feb 14, 2012 at 9:59 AM, Michael S. Tsirkin wrote: > > On Tue, Feb 14, 2012 at 07:53:26AM +1100, ronnie sahlberg wrote: > >> On Tue, Feb 14, 2012 at 7:42 AM, ronnie sahlberg > >> wrote: > >> > On Tue, Feb 14, 2012 at 2:12 AM, Hannes Reinecke wrote: > >> >> On 02/13/2012 02:18 PM, Michael S. Tsirkin wrote: > >> >>> On Tue, Feb 14, 2012 at 12:13:36AM +1100, ronnie sahlberg wrote: > >> >>>> On Tue, Feb 14, 2012 at 12:00 AM, Michael S. Tsirkin wrote: > >> >>>>> On Mon, Feb 13, 2012 at 02:54:03PM +0200, Dor Laor wrote: > >> >>>>>> Only if you use the pci multi-function option but that kills > >> >>>>>> standard hot unplug > >> >>>>> > >> >>>>> It doesn't kill it as such, rather you can't unplug luns individually. > >> >>>> > >> >>>> Isnt that just a consequence of the current implementation rather than > >> >>>> a SCSI limitation? > >> >>> > >> >>> Yes. > >> >>> > >> >>>> A different way to do hoplug could be to flag all devices as removable > >> >>>> in the standard inq page then > >> >>>> leave the LUN there persistently and what you remove/add is not the > >> >>>> LUN device itself but just the media in the device. > >> >>>> > >> >>>> Instead of hot-plug remove the LUN, ?hot-plug becomes "media eject" or > >> >>>> "media insert". > >> >>>> The device remains present all time, you never remove it, but instead > >> >>>> hot-plug controls if the media is present or not. > >> >>>> > >> >>>> > >> >>>> This would require implementing at least START_STOP_UNIT and > >> >>>> PREVENT_ALLOW_MEDIUM_REMOVAL opcode emulation from SBC. > >> >>>> > >> >>>> > >> >>>> regards > >> >>>> ronnie sahlberg > >> >>> > >> >>> That would work. > >> >>> > >> >> Or we simply use the Peripheral Qualifier that the device is gone; > >> >> eg we could simply set PQ = 1, return sense code 0x25/00 and be done > >> >> with ... > >> >> > >> > > >> > That is still similar to "rip a device out from the guest without notice" > >> > and can cause the guest to be "surprised". > >> > > >> > > >> > Removable media is standard feature in SCSI SBC (and other commandsets). > >> > The nice part of removable media is that it activates a contract > >> > between the device and the guest > >> > to prevent removal of the media when the guest depends on the media > >> > not being removed. > >> > > >> > I.e. ?If you have a SBC device with the removable-media bit set, > >> > this is used to tell the initiator "this media can be removed, be > >> > prepared that this might happen". > >> > So when you mount such a SBC device in the guest, the guest will issue > >> > a "PREVENT_ALLOW_MEDIUM_REMOVAL" > >> > to tell the device "this medium is in use and may not be removed". > >> > > >> > >> What I mean is that if /dev/sdb is removable, > >> if you mount this as ? "mount /dev/sdb1 /mnt" > >> this will automatically cause the guest kernel to send a > >> PREVENT_ALLOW_MEDIUM_REMOVAL to /dev/sdb to prevent removal. > >> > >> When you "umount /dev/sdb1" ? the kernel/guest will automagically send > >> PREVENT_ALLOW_MEDIUM_REMOVEAL to /dev/sdb and allow removal of the > >> media again. > >> > >> > >> If you capture this command and track the "prevent/allow removal > >> status" ?you automatically get a channel where qemu will > >> know when it is safe to unplug the device ?and when it is not safe to > >> unplug the device. > >> This is a nice feature. > > > > Presumably there's a way for device to notify the OS > > that user requested removal, as well? > > > I think that is done by responding with sense to one of the commands, > like the every few second TEST_UNIT_READY that the > initiator/guest-kernel will send. Does it do this even for mounted media? I didn't realize ... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/