[systemd-devel] udev virtio by-path naming

[Daniel P. Berrange]

On Wed, Mar 01, 2017 at 04:02:53PM +0100, Viktor Mihajlovski wrote:
> On 01.03.2017 04:30, Zbigniew Jędrzejewski-Szmek wrote:
> > On Tue, Feb 28, 2017 at 09:47:42AM +0100, Viktor Mihajlovski wrote:
> >>>>>> One could argue about back-level compatibility, but virtio by-path
> >>>>>> naming has changed multiple times. We have seen virtio-pci-virtio<n>
> >>>>>> (not predictable), pci-<busid> and virtio-pci-<busid> already. It
> >>>>>> might be a good time now to settle on a common approach for all
> >>>>>> virtio types.
> >>>>>>
> >>>>>> For the reasons above, I'd vote for <subsystem>-<busid>, which
> >>>>>> would work for PCI and CCW, not sure about ARM MMIO though.
> > 
> > It seems that there's agreement that <subsystem>-<busid> is the right
> > approach.
> > 
> > Ideally we would keep the virtio-pci-<busid> links as they appear
> > right now, for backwards compatibility, just for the pci devices, and
> > mark them as deprecated (dunno where, maybe just in NEWS), and add the
> > code to make the links.
> > 
> > I haven't looked at the code, maybe we just do this with the right
> > udev rule, and also stick the deprecation comment there?
> > 
> > Zbyszek
> > 
> I've posted a github pull request [1], and would appreciate review
> feedback. As I am lacking an ARM setup, it would also be nice if someone
> with ARM skills could have a look as well.

FYI you can install ARM7 guests on an x86_64 host, using pre-built Fedora
images

  https://fedoraproject.org/wiki/QA:Testcase_Virt_ARM_on_x86

NB, this will install the guest using virtio-pci. So if you want to
see virtio-mmio in action, you'll need to edit the libvirt XML config
afterwards to add another disk, eg

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/data.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <address type='virtio-mmio'/>
    </disk>


> If wanted, I can take a stab at virtio-mmio, but would need the output
> of udevadm -a /dev/vda from a virtio-mmio system.

Presumably you mean 'udevadm info -a /dev/vda' ?  That reports the following,
given a basic Fedora 25 guest, with a virtio-mmio disk added as per the
guide above...

  looking at device '/devices/platform/a003e00.virtio_mmio/virtio3/block/vda':
    KERNEL=="vda"
    SUBSYSTEM=="block"
    DRIVER==""
    ATTR{alignment_offset}=="0"
    ATTR{badblocks}==""
    ATTR{cache_type}=="write back"
    ATTR{capability}=="50"
    ATTR{discard_alignment}=="0"
    ATTR{ext_range}=="256"
    ATTR{inflight}=="       0        0"
    ATTR{range}=="16"
    ATTR{removable}=="0"
    ATTR{ro}=="0"
    ATTR{serial}==""
    ATTR{size}=="2097152"
    ATTR{stat}=="      94        0     4208      285        0        0        0 
       0        0      100      280"

  looking at parent device '/devices/platform/a003e00.virtio_mmio/virtio3':
    KERNELS=="virtio3"
    SUBSYSTEMS=="virtio"
    DRIVERS=="virtio_blk"
    ATTRS{device}=="0x0002"
    ATTRS{features}=="0010101101110000000000000000110000000000000000000000000000
000000"
    ATTRS{status}=="0x00000007"
    ATTRS{vendor}=="0x554d4551"

  looking at parent device '/devices/platform/a003e00.virtio_mmio':
    KERNELS=="a003e00.virtio_mmio"
    SUBSYSTEMS=="platform"
    DRIVERS=="virtio-mmio"
    ATTRS{driver_override}=="(null)"

  looking at parent device '/devices/platform':
    KERNELS=="platform"
    SUBSYSTEMS==""
    DRIVERS==""



Regards,
Daniel
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