[Qemu-devel] [Bug 1736655] Re: 2k3/xp guests w/virtio-net randomly DHCP fail on boot

[ChristianEhrhardt]

I wanted an XP guest testbed anyway for some time, so this was the perfect 
reason to create one.
# virtio drivers from [1] and otherwise a "normal" virt-manager setup of a 
winxp sp3 (32bit) guest

- Modified to use virtio for net
- Modified to have the virtio drivers as floppy
- Installed virtio drivers for network afer base install

So after that I assume I'm at the same stage you are.
- WinXP Guest
- Virtio Driver for network
- Host provides DHCP to a bridged network

I set that to a rebot loop and checked the internet connection through
the dhcp virtiop net after reboot. This worked through 10 reboots
without an issue, but then IIRC with vhost ioeventfd was on all the
time.

I realized the change identified by you should only make a differenc on 
non-vhost virtio-net.
But libvirt will make use of vhost automatically if available, so I set the 
interface to use driver qemu explicitly.

Another 10 reboots without issue - the virtio version is of 7/19/2017 version 
51.75.104.14100
There must be something more to your case, so please if you have more info how 
to trigger the case let us know.

I really think I have the same case you were describing as affected by the 
change you identified:
$ virsh qemu-monitor-command --hmp winxp 'info network'
net0: index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:ce:ca:72
 \ hostnet0: index=0,type=tap,fd=26
Here from qtree on the device [2] ioeventfd is on.

Could you try and run it with vhost and see if this changes behavior it
for you?

[1]: 
https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/stable-virtio/virtio-win_amd64.vfd
[2]: http://paste.ubuntu.com/26123654/

** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1736655

Title:
  2k3/xp guests w/virtio-net randomly DHCP fail on boot

Status in QEMU:
  Incomplete
Status in qemu package in Ubuntu:
  Incomplete

Bug description:
  Host:
  Debian GNU/Linux 9 with Linux 4.13.0-0.bpo.1-amd64
  QEMU 2.10.1

  Guest:
  Windows 2003 Standard SP2 (x64)
  Windows XP SP3 (i386)

  QEMU command line:
  http://cfp.vim-cn.com/cbdF3

  Description:
  After upgrading from QEMU 2.8 to 2.10.1, my Windows 2003 x64 and Windows XP 
guests with "virtio-net-pci" NIC would randomly fail to aquire DHCP address on 
boot. When it fails, cycle disable/enable the connection in Control Panel could 
make it connect successfully. As an immediate workaround, I switched to the 
RTL8139 NIC which works fine. Further investigation showed that manually 
reverting commit '4a3f03ba8dbf53fce36d0c1dd5d0cc0f340fe5f3' on top of 2.10.1 
"fixed" the problem.

  Here are the bisect test results:
  git branch 97cd965: 17 boots, 5 failures  (Feb 18)
  git branch 77424a4: 27 boots, 0 failure   (Jan 09)
  git branch c25d97c: 7 boots, 2 failures   (Feb 01)
  git branch 4a3f03b: 25 boots, 8 failures  (Jan 19)
  git branch 39f099e: 60 boots, 0 failure   (Jan 18)
  2.10.1 with revert: 194 boots, 0 failure
  2.10.1 without revert: 30 boots, 4 failures

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