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

[Bruno Alvisio]

Hello John,

Thanks. Yes, typo when I wrote the e-mail.

It might be possible that XEN does that (I will ask in the XEN forum). However, I have noticed that it is not the case for all of the VMs I have launched. In some of them I can query the block devices even after a long time the VM has been running.

I was wondering if the device is removed in case the disk is corrupted or something. When I mention it runs normally, I can log into ithe VM and perform read/write operations such creating files.

Also, is there an easy way to log all qemu events so that I can see what might be going on with the 'ide' device?

Thanks,

Bruno

On Thu, May 25, 2017 at 11:18 AM, John Snow <address@hidden> wrote:

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=""
>