Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758130Ab2BMUx3 (ORCPT ); Mon, 13 Feb 2012 15:53:29 -0500 Received: from mail-tul01m020-f174.google.com ([209.85.214.174]:40591 "EHLO mail-tul01m020-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754169Ab2BMUx1 convert rfc822-to-8bit (ORCPT ); Mon, 13 Feb 2012 15:53:27 -0500 MIME-Version: 1.0 In-Reply-To: References: <4F313526.2050907@redhat.com> <4F3390FB.80107@redhat.com> <1329077777.21613.60.camel@dabdike.int.hansenpartnership.com> <4F38B657.7060405@de.ibm.com> <4F38C27E.7030300@redhat.com> <1329136806.9333.383.camel@haakon2.linux-iscsi.org> <4F3907EB.4030402@redhat.com> <20120213130005.GB26773@redhat.com> <20120213131848.GD26773@redhat.com> <4F39287A.9030808@suse.de> Date: Tue, 14 Feb 2012 07:53:26 +1100 Message-ID: Subject: Re: Pe: [PATCH v5 1/3] virtio-scsi: first version From: ronnie sahlberg To: Hannes Reinecke Cc: "Michael S. Tsirkin" , 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3156 Lines: 80 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. -- 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/