Re: [Qemu-devel] Behavior of QMP "query-block"

[John Snow]

On 05/25/2017 12:27 AM, Bruno Alvisio wrote:
> Hello all,
> 
> Summary
> 
> I am using XEN hypervisor to run a HVM with a QEMU backed disk. After I
> start the HVM I use QMP "query-block" command to see the devices of the VM.
> Initially the command returns the disk that I set as part of the
> configuration. After a few seconds the a DEVICE_DELETE event occurs (for
> device nic0) and after that the "query-block" command returns an empty
> result.
> 
> QEMU Version: 4.6.5

I assume this is the KVM version.

> Arch: x86-64
> QMP : 2.2.1

And I assume this is the QEMU version.

> 
> Note:
> 1. I was not performing any activity on the VM when the event occurs.
> 2. After the event, the QEMU process is still alive and the VM runs
> normally.
> 3. This behavior is consistently reproduced.
> 
> 
> Any help on how can I debug this issue would be greatly appreciated .
> 
> Thanks,
> 
> Bruno
> 

I'm not very familiar with XEN, I do know that it likes to add more
devices than it needs and then deletes them before starting the VM
proper. The VM actually still runs normally despite the fact that query
block returns no information? ...

CCing qemu-block.

--js

> 
> 
> DETAILED LOGS
> 
> I am using XEN hypervisor to run a HVM with QEMU backed disk. When I start
> the HVM I see the following QEMU process started:
> 
> root      2199     1  0 18:57 ?        00:00:02
> /usr/local/lib/xen/bin/qemu-system-i386
> -xen-domid 3 -chardev socket,id=libxl-cmd,path=/var/
> run/xen/qmp-libxl-3,server,nowait -no-shutdown -mon
> chardev=libxl-cmd,mode=control -chardev socket,id=libxenstat-cmd,path=
> /var/run/xen/qmp-libxenstat-3,server,nowait -mon
> chardev=libxenstat-cmd,mode=control -nodefaults -no-user-config -name
> debianL2 -vnc :0,to=99 -display none -serial pty -device
> cirrus-vga,vgamem_mb=8 -boot order=d -device
> rtl8139,id=nic0,netdev=net0,mac=00:16:3e:1b:d0:7e
> -netdev type=tap,id=net0,ifname=vif3.0-emu,script=no,downscript=no -machine
> xenfv -m 1016 -drive file=/home/balvisio/debian-
> disk.img,if=ide,index=0,media=disk,format=raw,cache=writeback -drive
> if=ide,index=2,readonly=on,media=cdrom,id=ide-5632,file=/
> home/balvisio/debian-live-8.7.1-amd64-gnome-desktop.iso,format=raw
> 
> After launching the VM, I connected to the QMP socket:
> 
> # rlwrap -C qmp socat STDIO UNIX:/var/run/xen/qmp-libxl-2
> 
> {"QMP": {"version": {"qemu": {"micro": 1, "minor": 2, "major": 2},
> "package": ""}, "capabilities": []}}
> 
> {"execute":"qmp_capabilities"}
> 
> {"return": {}}
> 
> I issue the "query-block" command and I get:
> 
> {"execute":"query-block"}
> 
> {"return": [{"io-status": "ok", "device": "ide0-hd0", "locked": false,
> "removable": false, "inserted": {"iops_rd": 0, "detect_zeroes": "off",
> "image": {"virtual-size": 10737418240, "filename":
> "/home/balvisio/debian-disk.img", "format": "raw", "actual-size":
> 4940075008, "dirty-flag": false}, "iops_wr": 0, "ro": false,
> "backing_file_depth": 0, "drv": "raw", "iops": 0, "bps_wr": 0, "encrypted":
> false, "bps": 0, "bps_rd": 0, "file": "/home/balvisio/debian-disk.img",
> "encryption_key_missing": false}, "type": "unknown"}]}
> 
> 
> 
> After a few seconds, the following event happens asynchronoausly:
> 
> {"timestamp": {"seconds": 1495590969, "microseconds": 898981}, "event":
> "DEVICE_DELETED", "data": {"device": "nic0", "path":
> "/machine/peripheral/nic0"}}
> 
> After that event, I perform a "query-block" command again but now the block
> device is gone:
> 
> {"execute":"query-block"}
> 
> {"return": []}
> 
> 
> Xen Config File Used
> 
> kernel="/usr/local/lib/xen/boot/hvmloader"
> 
> builder='hvm'
> 
> memory=1024
> 
> vcpus=1
> 
> name="debianL2"
> 
> vfb = ['type=vnc']
> 
> vif= ['bridge=xenbr0']
> 
> boot='b'
> 
> disk=['file:/home/balvisio/debian-disk.img,xvda,w']
> 
> acpi=1
> 
> device_model_version='qemu-xen'
> 
> serial='pty'
> 
> vnc=1
> 
> vnclisten=""
> 
> vncpasswd=""
>