Re: [Qemu-devel] [PATCH 10/13] Implement scsi device destruction

[Artyom Tarasenko <atar4qemu@googlemail.com>]

2009/9/25 Markus Armbruster <armbru@redhat.com>:
> Gerd Hoffmann <kraxel@redhat.com> writes:
>
>>   Hi,
>>
>>> If I understand this correctly, SCSI devices "overwrite": if you add a
>>> new one with an existing SCSI ID, the old one gets disconnected
>>> automatically.  Isn't that inconsistent with other buses?  PCI,
>>> specifically.  Question applies before your patch already.
>>
>> Yes, this is correct.
>> I've just maintained current behavior.
>>
>> To extend that question:  While playing with that I've noticed linux
>> does not automagically find the a scsi disk hot-plugged in.  After
>> reboot (and the scsi bus rescan triggered by that) it finds the
>> disk. Reloading the driver module probably would have worked too.  We
>> don't signal the guest in any way it got a new disk, so this isn't
>> exactly surprising.  Is this just a emulation limitation?  Or a
>> limitation of the emulated scsi host adapters?
>
> What appens when you hotplug or just switch on a real SCSI device?  Does
> Linux pick it up automatically?  Long ago when I last tried that, I
> think I had to do a magic write to sysfs to make it look for the device.

I guess it wasn't magic, but an official way of doing it. At least
SCSI-2 controllers didn't get any notification signal on a hot-plug.
I used to do it with
echo "scsi add-single-device 0 0 3 0" > /proc/scsi/scsi