当虚拟机运行起来后，管理员还可以获取虚拟机运行状态的数据，动态添加支持热插拔的设备。这是如何实现的呢？通过Qemu的monitor，libvirt很多功能也都是通过Qemu的monitor机制实现的，Qemu的很多高级功能也需要通过monitor的命令来实现。总之monitor很重要！
几个关键词：QMP，HMP。
Qemu monitor主要由三部分构成monitor client，QMP，monitor server。相关详细介绍可以看Qemu源码doc中的qmp相关部分！
HMP 命令行列表：
# acl 相关命令，acl是什么？
acl_add aclname match allow|deny [index] -- add a match rule to the access control list
acl_policy aclname allow|deny -- set default access control list policy
acl_remove aclname match -- remove a match rule from the access control list
acl_reset aclname -- reset the access control list
acl_show aclname -- list rules in the access control list
# 内存balloon相关命令
balloon target -- request VM to change its memory allocation (in MB)
# block job相关命令
block_job_cancel [-f] device -- stop an active background block operation (use -f
if the operation is currently paused)
block_job_complete device -- stop an active background block operation
block_job_pause device -- pause an active background block operation
block_job_resume device -- resume a paused background block operation
block_job_set_speed device speed -- set maximum speed for a background block operation
# block的一些命令
block_passwd block_passwd device password -- set the password of encrypted block devices
block_resize device size -- resize a block image
block_set_io_throttle device bps bps_rd bps_wr iops iops_rd iops_wr -- change I/O throttle limits for a block drive
block_stream device [speed [base]] -- copy data from a backing file into a block device
boot_set bootdevice -- define new values for the boot device list
change device filename [format] -- change a removable medium, optional format
chardev-add args -- add chardev
chardev-remove id -- remove chardev
client_migrate_info protocol hostname port tls-port cert-subject -- send migration info to spice/vnc client
closefd closefd name -- close a file descriptor previously passed via SCM rights
commit device|all -- commit changes to the disk images (if -snapshot is used) or backing files
cpu index -- set the default CPU
cpu-add id -- add cpu
c|cont -- resume emulation
delvm tag|id -- delete a VM snapshot from its tag or id
device_add driver[,prop=value][,...] -- add device, like -device on the command line
device_del device -- remove device
drive_add [[:]:]
[file=file][,if=type][,bus=n]
[,unit=m][,media=d][,index=i]
[,cyls=c,heads=h,secs=s[,trans=t]]
[,snapshot=on|off][,cache=on|off]
[,readonly=on|off][,copy-on-read=on|off] -- add drive to PCI storage controller
drive_backup [-n] [-f] device target [format] -- initiates a point-in-time
copy for a device. The device's contents are
copied to the new image file, excluding data that
is written after the command is started.
The -n flag requests QEMU to reuse the image found
in new-image-file, instead of recreating it from scratch.
The -f flag requests QEMU to copy the whole disk,
so that the result does not need a backing file.
drive_del device -- remove host block device
drive_mirror [-n] [-f] device target [format] -- initiates live storage
migration for a device. The device's contents are
copied to the new image file, including data that
is written after the command is started.
The -n flag requests QEMU to reuse the image found
in new-image-file, instead of recreating it from scratch.
The -f flag requests QEMU to copy the whole disk,
so that the result does not need a backing file.
dump-guest-memory [-p] filename [begin] [length] -- dump guest memory to file
begin(optional): the starting physical address
length(optional): the memory size, in bytes
eject [-f] device -- eject a removable medium (use -f to force it)
expire_password protocol time -- set spice/vnc password expire-time
gdbserver [device] -- start gdbserver on given device (default 'tcp::1234'), stop with 'none'
getfd getfd name -- receive a file descriptor via SCM rights and assign it a name
help|? [cmd] -- show the help
host_net_add tap|user|socket|vde|netmap|dump [options] -- add host VLAN client
host_net_remove vlan_id name -- remove host VLAN client
hostfwd_add [vlan_id name] [tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport -- redirect TCP or UDP connections from host to guest (requires -net user)
hostfwd_remove [vlan_id name] [tcp|udp]:[hostaddr]:hostport -- remove host-to-guest TCP or UDP redirection
i /fmt addr -- I/O port read
info [subcommand] -- show various information about the system state
loadvm tag|id -- restore a VM snapshot from its tag or id
log item1[,...] -- activate logging of the specified items
logfile filename -- output logs to 'filename'
mce [-b] cpu bank status mcgstatus addr misc -- inject a MCE on the given CPU [and broadcast to other CPUs with -b option]
memsave addr size file -- save to disk virtual memory dump starting at 'addr' of size 'size'
migrate [-d] [-b] [-i] uri -- migrate to URI (using -d to not wait for completion)
-b for migration without shared storage with full copy of disk
-i for migration without shared storage with incremental copy of disk (base image shared between src and destination)
migrate_cancel -- cancel the current VM migration
migrate_set_cache_size value -- set cache size (in bytes) for XBZRLE migrations,the cache size will be rounded down to the nearest power of 2.
The cache size affects the number of cache misses.In case of a high cache miss ratio you need to increase the cache size
migrate_set_capability capability state -- Enable/Disable the usage of a capability for migration
migrate_set_downtime value -- set maximum tolerated downtime (in seconds) for migrations
migrate_set_speed value -- set maximum speed (in bytes) for migrations. Defaults to MB if no size suffix is specified, ie. B/K/M/G/T
mouse_button state -- change mouse button state (1=L, 2=M, 4=R)
mouse_move dx dy [dz] -- send mouse move events
mouse_set index -- set which mouse device receives events
nbd_server_add nbd_server_add [-w] device -- export a block device via NBD
nbd_server_start nbd_server_start [-a] [-w] host:port -- serve block devices on the given host and port
nbd_server_stop nbd_server_stop -- stop serving block devices using the NBD protocol
netdev_add [user|tap|socket|hubport|netmap],id=str[,prop=value][,...] -- add host network device
netdev_del id -- remove host network device
nmi -- inject an NMI on all guest's CPUs
o /fmt addr value -- I/O port write
object_add [qom-type=]type,id=str[,prop=value][,...] -- create QOM object
object_del id -- destroy QOM object
pcie_aer_inject_error [-a] [-c] id [ []] -- inject pcie aer error
-a for advisory non fatal error
-c for correctable error
= qdev device id
= error string or 32bit
= 32bit x 4
= 32bit x 4
pmemsave addr size file -- save to disk physical memory dump starting at 'addr' of size 'size'
p|print /fmt expr -- print expression value (use $reg for CPU register access)
qemu-io [device] "[command]" -- run a qemu-io command on a block device
q|quit -- quit the emulator
ringbuf_read device size -- Read from a ring buffer character device
ringbuf_write device data -- Write to a ring buffer character device
savevm [tag|id] -- save a VM snapshot. If no tag or id are provided, a new snapshot is created
screendump filename -- save screen into PPM image 'filename'
sendkey keys [hold_ms] -- send keys to the VM (e.g. 'sendkey ctrl-alt-f1', default hold time=100 ms)
set_link name on|off -- change the link status of a network adapter
set_password protocol password action-if-connected -- set spice/vnc password
singlestep [on|off] -- run emulation in singlestep mode or switch to normal mode
snapshot_blkdev [-n] device [new-image-file] [format] -- initiates a live snapshot
of device. If a new image file is specified, the
new image file will become the new root image.
If format is specified, the snapshot file will
be created in that format.
The default format is qcow2. The -n flag requests QEMU
to reuse the image found in new-image-file, instead of
recreating it from scratch.
snapshot_blkdev_internal device name -- take an internal snapshot of device.
The format of the image used by device must
support it, such as qcow2.
snapshot_delete_blkdev_internal device name [id] -- delete an internal snapshot of device.
If id is specified, qemu will try delete
the snapshot matching both id and name.
The format of the image used by device must
support it, such as qcow2.
stop -- stop emulation
stopcapture capture index -- stop capture
sum addr size -- compute the checksum of a memory region
system_powerdown -- send system power down event
system_reset -- reset the system
system_wakeup -- wakeup guest from suspend
trace-event name on|off -- changes status of a specific trace event
usb_add device -- add USB device (e.g. 'host:bus.addr' or 'host:vendor_id:product_id')
usb_del device -- remove USB device 'bus.addr'
watchdog_action [reset|shutdown|poweroff|pause|debug|none] -- change watchdog action
wavcapture path [frequency [bits [channels]]] -- capture audio to a wave file (default frequency=44100 bits=16 channels=2)
x /fmt addr -- virtual memory dump starting at 'addr'
xp /fmt addr -- physical memory dump starting at 'addr'