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


From: Bruno Alvisio
Subject: [Qemu-devel] Behavior of QMP "query-block"
Date: Wed, 24 May 2017 21:27:29 -0700

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
Arch: x86-64
QMP : 2.2.1

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



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=""


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