On Tue, Feb 14, 2012 at 07:53:26AM +1100, ronnie sahlberg wrote: > On Tue, Feb 14, 2012 at 7:42 AM, ronnie sahlberg > <ronniesahlberg@xxxxxxxxx> wrote: > > On Tue, Feb 14, 2012 at 2:12 AM, Hannes Reinecke <hare@xxxxxxx> 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 <mst@xxxxxxxxxx> 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? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
