devel/migration/CPR.rst

8 the cpr-reboot and cpr-transfer modes are available.
18 cpr-reboot mode
19 ---------------
23 resumes by running QEMU with the ``-incoming`` option.  Because the
25 be a type that streams data from one instance to the other.
38 ``guest-suspend-ram`` command to the QEMU guest agent.  The agent
39 must be pre-installed in the guest, and the guest must support
48 memory, such as ``memory-backend-file,share=on``, and that the
49 ``x-ignore-shared`` capability be set.  This combination allows memory
54   * Set the migration mode parameter to ``cpr-reboot``.
55   * Set the ``x-ignore-shared`` capability if desired.
58     provided the command captures all the data from the outgoing side,
59     and provides all the data to the incoming side.
63   * Start QEMU with the ``-incoming defer`` option.
64   * Set the migration mode parameter to ``cpr-reboot``.
65   * Set the ``x-ignore-shared`` capability if desired.
66   * Issue the ``migrate-incoming`` command.
74   # qemu-kvm -monitor stdio
75   -object memory-backend-file,id=ram0,size=4G,mem-path=/dev/dax0.0,align=2M,share=on -m 4G
80   (qemu) migrate_set_parameter mode cpr-reboot
81   (qemu) migrate_set_capability x-ignore-shared on
82   (qemu) migrate -d file:vm.state
92   # qemu-kvm ... -incoming defer
95   (qemu) migrate_set_parameter mode cpr-reboot
96   (qemu) migrate_set_capability x-ignore-shared on
105   # qemu-kvm -monitor stdio
106   -object memory-backend-file,id=ram0,size=4G,mem-path=/dev/dax0.0,align=2M,share=on -m 4G
107   -device vfio-pci, ...
108   -chardev socket,id=qga0,path=qga.sock,server=on,wait=off
109   -device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0
115   # echo '{"execute":"guest-suspend-ram"}' | ncat --send-only -U qga.sock
119   (qemu) migrate_set_parameter mode cpr-reboot
120   (qemu) migrate_set_capability x-ignore-shared on
121   (qemu) migrate -d file:vm.state
131   # qemu-kvm ... -incoming defer
134   (qemu) migrate_set_parameter mode cpr-reboot
135   (qemu) migrate_set_capability x-ignore-shared on
146 cpr-reboot mode may not be used with postcopy, background-snapshot,
149 cpr-transfer mode
150 -----------------
158 The user starts new QEMU on the same host as old QEMU, with command-
159 line arguments to create the same machine, plus the ``-incoming``
160 option for the main migration channel, like normal live migration.
161 In addition, the user adds a second -incoming option with channel
162 type ``cpr``.  This CPR channel must support file descriptor transfer
166 adding a second migration channel of type ``cpr`` in the channels
171 New QEMU reads the CPR channel before opening a monitor, hence
172 the CPR channel cannot be specified in the list of channels for a
173 migrate-incoming command.  It may only be specified on the command
181 The VM must be started with the ``-machine aux-ram-share=on``
183 a memory-backend object) to be allocated by mmap'ing a memfd.
187   * Set the migration mode parameter to ``cpr-transfer``.
188   * Issue the ``migrate`` command, containing a main channel and
189     a cpr channel.
192   * Start new QEMU with two ``-incoming`` options.
199 cpr-transfer mode may not be used with postcopy, background-snapshot,
202 memory-backend-epc is not supported.
204 The main incoming migration channel address cannot be a file type.
206 If the main incoming channel address is an inet socket, then the port
209 When using ``-incoming defer``, you must issue the migrate command to
211 QEMU blocks waiting to read from the cpr channel before starting its
212 monitor, and old QEMU does not write to the channel until the migrate
214 main migration channel until you issue the migrate incoming command.
216 Example 1: incoming channel
223 HMP cannot specify a CPR channel.  Some QMP responses are omitted for
230   # qemu-kvm -qmp stdio
231   -object memory-backend-file,id=ram0,size=4G,
232   mem-path=/dev/shm/ram0,share=on -m 4G
233   -machine memory-backend=ram0
234   -machine aux-ram-share=on
236                                         # qemu-kvm -monitor stdio
237                                         -incoming tcp:0:44444
238                                         -incoming '{"channel-type": "cpr",
244   {"execute": "query-status"}
248   {"execute":"migrate-set-parameters",
249    "arguments":{"mode":"cpr-transfer"}}
252     {"channel-type": "main",
255     {"channel-type": "cpr",
263   {"execute": "query-status"}
270 This example uses ``-incoming defer`` to hot plug a device before
271 accepting the main migration channel.  Again note you must issue the
280   # qemu-kvm -monitor stdio
281   -object memory-backend-file,id=ram0,size=4G,
282   mem-path=/dev/shm/ram0,share=on -m 4G
283   -machine memory-backend=ram0
284   -machine aux-ram-share=on
286                                         # qemu-kvm -monitor stdio
287                                         -incoming defer
288                                         -incoming '{"channel-type": "cpr",
295    "arguments": {"driver": "pcie-root-port"}}
297   {"execute":"migrate-set-parameters",
298    "arguments":{"mode":"cpr-transfer"}}
301     {"channel-type": "main",
304     {"channel-type": "cpr",
311                                         (qemu) device_add pcie-root-port
316   {"execute": "query-status"}
323 cpr-transfer mode is based on a capability to transfer open file