Re: Running mipsel guest under libvirt/qemu

[James Cowgill <jcowgill@debian.org>]

Hi,

On 05/06/17 12:10, Christoph Biedl wrote:
> Hello,
> 
> in a desperate attempt to understand #852962, thus salvaging ycmd and
> youcompleteme for stretch, I tried to set up an emulated mipsel machine
> using libvirt/qemu, and failed horribly. There are tons of documents
> out there, many years old, contradicting, not helping.
> 
> So: Is this feasible at all? I could use a pointer then.
> 
> So far: Create a virtual machine, with installer CD and virtual disk.
> Then libvirt needs a patch by Aurilien[1][2]. Then libvirt complains
> about mips_bios.bin although some pages[3]  state this was no
> longer required. Providing a dummy image, the machine starts, but shows
> just a blank screen and qemu eats 100% CPU. Then booting via "Direct
> kernel boot", ditto. I've tried several "console=" parameters, no
> avail. Perhaps libvirt plays tricks on me, wasn't the first time.

You have to use direct kernel booting on mips. If you provide a dummy
bootloader, qemu will execute it and just hang.

I remember trying to use libvirt some time ago on mips and having to
manually specify the base address of the serial port on malta. I found
this config file but its a few years old so it might not work anymore.

> It *is* possible to start qemu-system-mipsel directly, with an
> additional '-serial stdio' parameter, but for reasons I'd really like to
> control the machine using libvirt, and I fail to see how to fiddle the
> kernel console into the libvirt terminal.
> 
> - What did I miss?
> - How comes appearently nobody encounters such issues?

I expect there are very few users of qemu-mipsel with libvirt. Some of
the issues you've encountered may be genuine bugs.

Thanks,
James

<domain type='qemu' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <name>debian-vm-1-qemu1</name>
  <uuid>c48e51ea-ba43-4de6-bd20-21469badae9e</uuid>
  <memory unit='KiB'>2097152</memory>
  <currentMemory unit='KiB'>2097152</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <os>
    <type arch='mips64el' machine='malta'>hvm</type>
    <kernel>/var/lib/libvirt/boot/vmlinux-mips64el</kernel>
    <initrd>/var/lib/libvirt/boot/initrd-mips64el</initrd>
    <cmdline>root=/dev/vda console=ttyS0 mem=2048m net.ifnames=0</cmdline>
    <boot dev='hd'/>
  </os>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-system-mips64el</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/debian-vm-1-qemu1'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </disk>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='usb' index='0' model='piix3-uhci'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
    </controller>
    <serial type='pty'>
      <target port='0'/>
      <address type='isa' iobase='0x3f8' irq='0x4'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
      <address type='isa' iobase='0x3f8' irq='0x4'/>
    </console>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </memballoon>
  </devices>
  <qemu:commandline>
    <qemu:arg value='-cpu'/>
    <qemu:arg value='MIPS64R2-generic'/>
  </qemu:commandline>
</domain>

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