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 but after a few seconds the "query-block" command returns an
empty result.
KVM Version: 4.6.5
Arch: x86-64
QEMU : 2.2.1
I was expecting to see the device information in QEMU such as:
{"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"}]}
I wanted to understand how the storage subsystem work for QEMU backed
disks. Any help and pointers in the code would be great.
Eventually I would like to implement a feature in XEN to allow migration of
instances with local disks.
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-dis
k.img,if=ide,index=0,media=disk,format=raw,cache=writeback -drive
if=ide,index=2,readonly=on,media=cdrom,id=ide-5632,file=/hom
e/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": []}
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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