Re: [Qemu-devel] [RFC PATCH 1/5] qdev: Create qdev_get_dev_path()

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2010-06-16 at 10:23 +0200, Markus Armbruster wrote:
> Alex Williamson <alex.williamson@redhat.com> writes:
> 
> > On Tue, 2010-06-15 at 12:28 +0100, Paul Brook wrote:
> >> > > Alex proposed to disambiguate by adding "identified properties of the
> >> > > immediate parent bus and device" to the path component.  For PCI, these
> >> > > are dev.fn.  Likewise for any other bus where devices have unambigous
> >> > > bus address.  The driver name carries no information!
> >> > 
> >> > From user POV, driver names are very handly to address a device
> >> > intuitively - except for the case you have tones of devices on the same
> >> > bus that are handled by the same driver. For that case we need to
> >> > augment the device name with a useful per-bus ID, derived from the bus
> >> > address where available, otherwise based on instance numbers.
> >> 
> >> This is where I think you're missing a trick. We don't need to augment the 
> >> name, we just need to allow the bus id to be used instead.
> >
> > For the case of a hot remove, I agree.  If the user specifies "pci_del
> > pci.0/03.0", that's completely sufficient because we don't care what's
> > in that slot, just remove it.  However, I still see some use cases for
> > device names in the path.  Take for example:
> >
> > (A): /i440FX-pcihost/pci.0/e1000.05.0
> >
> > vs
> >
> > (B): /pci.0/05.0
> >
> > (removing both the root bridge driver name and the device driver name)
> 
> / is the main system bus.  System bus defines no bus address at the
> moment.  Therefore, you have to use the driver name i440FX-pcihost.

So is the general rule "If a device's parent bus does not provide an
address, print device name"?

> /i440FX-pcihost/pci.0 is the PCI bus.  PCI bus defines a bus address:
> dev.fn.  Therefore, you can either use the bus address @05.0, or the
> driver name e1000.
> 
> We have "/i440FX-pcihost/pci.0/e1000" vs. "/i440FX-pcihost/pci.0/@05.0".

I object to being able to use anything but an address under a bus that
supports hotplug, but that aside, I think the paths for my example
system look like below.  Note that anything behind and including the $
is not the canonical path, that begins the free form, usage specific
string, here filled by missing device names (open to suggestions other
than $ here).  Note that were isa devices do not have a bus identifier,
I'm using the device name, which I think follows the same rule as
i440FX-pcihost.  Can we agree this is the goal?  Thanks,

Alex

/i440FX-pcihost/pci.0/@00.0$i440FX
/i440FX-pcihost/pci.0/@01.0$PIIX3
/i440FX-pcihost/pci.0/@02.0$cirrus-vga
/i440FX-pcihost/pci.0/@01.0/isa.0/mc146818rtc
/i440FX-pcihost/pci.0/@01.0/isa.0/@0x3f8$isa-serial
/i440FX-pcihost/pci.0/@01.0/isa.0/@0x378$isa-parallel
/i440FX-pcihost/pci.0/@01.0/isa.0/i8042
/i440FX-pcihost/pci.0/@01.0/isa.0/isa-fdc
/i440FX-pcihost/pci.0/@03.0$i82551
/i440FX-pcihost/pci.0/@04.0$virtio-net-pci
/i440FX-pcihost/pci.0/@05.0$e1000
/i440FX-pcihost/pci.0/@06.0$rtl8139
/i440FX-pcihost/pci.0/@07.0$pcnet
/i440FX-pcihost/pci.0/@01.0/isa.0/@0x300$ne2k_isa
/i440FX-pcihost/pci.0/@01.1$piix3-ide
/i440FX-pcihost/pci.0/@01.1/ide.0/@0$ide-drive
/i440FX-pcihost/pci.0/@01.1/ide.1/@0$ide-drive
/i440FX-pcihost/pci.0/@01.2$piix3-usb-uhci
/i440FX-pcihost/pci.0/@01.3$PIIX4_PM
/i440FX-pcihost/pci.0/@01.3/i2c/@80$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@81$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@82$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@83$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@84$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@85$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@86$smbus-eeprom
/i440FX-pcihost/pci.0/@01.3/i2c/@87$smbus-eeprom
/i440FX-pcihost/pci.0/@08.0/scsi.0/@0$scsi-disk
/i440FX-pcihost/pci.0/@08.0/scsi.0/@3$scsi-disk
/i440FX-pcihost/pci.0/@08.0$lsi53c895a
/i440FX-pcihost/pci.0/@01.2/usb.0/@usb0/scsi.0/@0$scsi-disk
/i440FX-pcihost/pci.0/@01.2/usb.0/@usb0$usb-storage
/i440FX-pcihost/pci.0/@09.0$virtio-blk-pci