Re: [patch 14/23] QEMU/KVM: device hot-add

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

On Tue, Mar 04, 2008 at 01:30:42PM -0600, Anthony Liguori wrote:
> Daniel P. Berrange wrote:
> >On Tue, Mar 04, 2008 at 03:34:33PM -0300, Marcelo Tosatti wrote:
> >>Add monitor command to hot-add PCI devices (nic and drive).
> >[snip]
> >
> >  
> >>Index: kvm-userspace.hotplug/qemu/monitor.c
> >>===================================================================
> >>--- kvm-userspace.hotplug.orig/qemu/monitor.c
> >>+++ kvm-userspace.hotplug/qemu/monitor.c
> >>@@ -1354,6 +1354,7 @@ static term_cmd_t term_cmds[] = {
> >>     { "migrate_set_speed", "s", do_migrate_set_speed,
> >>       "value", "set maximum speed (in bytes) for migrations" },
> >>     { "cpu_set", "is", do_cpu_set_nr, "cpu [online|offline]", "change 
> >>     cpu state" },
> >>+    { "pci_add", "ss", device_hot_add, "nic|drive 
> >>[vlan=n][,macaddr=addr][,model=type] 
> >>[[file=file][,if=type][,bus=n][,unit=m][,media=d][index=i]]", "hotadd PCI 
> >>device" },
> >>    
> >
> >This syntax is not very nice IMHO. We should have explicit commands
> >for the different types of device,
> >
> >ie
> >
> >   nic_add [vlan=n][,macaddr=addr][,model=type]
> >   drive_add [[file=file][,if=type][,bus=n][,unit=m][,media=d][index=i]]
> >
> >ie, follow naming of the command line args   -nic, and -drive.
> >
> >This also keeps 'pci_add' as a command name available for future use to
> >do generic host->guest  pci device pass-through.
> >  
> 
> There is symmetry with pci_add and usb_add since usb_add takes either a 
> USB device identifier or the name of an emulated device along with 
> parameters.  So I prefer the pci_add syntax just to maintain consistency 
> with the rest of QEMU.

This is true, but the usb_add/remove syntax is horrible to work with. One
of the reasons I've not added  USB hotplug/remove to libvirt yet is the
difficulty (perhaps even impossibility) of reliably finding out the USB
device number associated with the device that was added. I guess ideally
the add command would have to print out / return the number associated
with the device, which libvirt could record for use when it later comes
time to remove the device.

Dan.
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