Re: [Qemu-devel] [patch 2/2] qemu: PCI device, disk and host network hot-add / hot-remove

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Feb 09, 2009 at 08:41:25PM -0200, Marcelo Tosatti wrote:
> On Mon, Feb 09, 2009 at 08:41:39AM +0000, Daniel P. Berrange wrote:
> > 
> > Also bear in mind that we need the ability to hot unplug devices which
> > were specified on the command line argv. For these we currently have
> > neither the pci <domain,bus,slot>, nor are given any 'name'. 
> 
> Any reason you can't discover <domain,bus,slot> from "info pci" ?
> (domain/bus are always zero at the moment).

'info pci' just gives you a list of PCI devices, and no direct means
to correlate these to devices listed in your command line argv.

eg, I launch QEMU with 3 nics

  qemu \
  ....more args...
  -net tap  -net nic,mac=01:02:03:04:05:01 \
  -net tap  -net nic,mac=01:02:03:04:05:02 \
  -net tap  -net nic,mac=01:02:03:04:05:03 \
  ....more args...

Then info pci shows this:

  ...snip...
  Bus  0, device   3, function 0:
    Ethernet controller: PCI device 10ec:8029
      IRQ 11.
      BAR0: I/O at 0xc100 [0xc1ff].
  Bus  0, device   4, function 0:
    Ethernet controller: PCI device 10ec:8029
      IRQ 9.
      BAR0: I/O at 0xc200 [0xc2ff].
  Bus  0, device   5, function 0:
    Ethernet controller: PCI device 10ec:8029
      IRQ 11.
      BAR0: I/O at 0xc300 [0xc3ff].
  ...snip...

I want to remove NIC with mac adress 01:02:03:04:05:02, but there is
no way to correlate this 'info pci' data to the NIC I wish to remove.
They may happen to appear in the same sorted order immediately after
startup, but if you've hot added & removed a couple of devices already,
then the order from 'info pci' can't easily map back to argv, unless
you very carefully tracked all changes.

> > Markus has previously suggested allowing <domain,bus,slot> to be
> > specified on the cli which would let us manually assign & use that
> > info for unplug.
> 
> > A device type specific unique naming would be useful too though. In
> > changeset r6220,  Mark McLoughlin provided the ability to give every
> > single NIC a unique name. I'd like to be able to use that name for
> > unplug. 
> 
> The NIC identifiers are not specific to PCI. So if you specify a
> non-PCI nic with the cli, you should not expect "pci_del name" to work.
> Now I see where you're getting at with the private discussion around
> "dev_add/dev_add".

Yes, if the device already had a unqiue identifier, it some ways it
would be easier to just be able todo  'nic_del 01:02:03:04:05:02'
Or for a SCSI disk 'drive_del bus=scsi,index=3'. QEMU ought to have
enough info internally to be able to map this to the PCI address it
needs to remove.

Daniel
-- 
|: Red Hat, Engineering, London   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|