On Tue, Feb 14, 2012 at 7:42 AM, ronnie sahlberg <ronniesahlb...@gmail.com> wrote: > On Tue, Feb 14, 2012 at 2:12 AM, Hannes Reinecke <h...@suse.de> 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 <m...@redhat.com> >>>> 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 kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
