devel/migration/CPR.rst

5 VM is migrated to a new QEMU instance on the same host.  It is
7 that run the VM, such as QEMU or even the host kernel.  At this time,
10 Because QEMU is restarted on the same host, with access to the same
13 guest block devices between quitting old QEMU and starting new QEMU.
21 In this mode, QEMU stops the VM, and writes VM state to the migration
22 URI, which will typically be a file.  After quitting QEMU, the user
23 resumes by running QEMU with the ``-incoming`` option.  Because the
24 old and new QEMU instances are not active concurrently, the URI cannot
32 software before restarting QEMU and resuming the VM.  Further, if
34 then the user may reboot to a new host kernel before restarting QEMU.
38 ``guest-suspend-ram`` command to the QEMU guest agent.  The agent
50 to be saved in place.  Otherwise, after QEMU stops the VM, all guest
60   * Quit when QEMU reaches the postmigrate state.
63   * Start QEMU with the ``-incoming defer`` option.
68     issued, then QEMU automatically resumes VM execution.
74   # qemu-kvm -monitor stdio
78   (qemu) info status
80   (qemu) migrate_set_parameter mode cpr-reboot
81   (qemu) migrate_set_capability x-ignore-shared on
82   (qemu) migrate -d file:vm.state
83   (qemu) info status
85   (qemu) quit
92   # qemu-kvm ... -incoming defer
93   (qemu) info status
95   (qemu) migrate_set_parameter mode cpr-reboot
96   (qemu) migrate_set_capability x-ignore-shared on
97   (qemu) migrate_incoming file:vm.state
98   (qemu) info status
105   # qemu-kvm -monitor stdio
109   -device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0
112   (qemu) info status
117   (qemu) info status
119   (qemu) migrate_set_parameter mode cpr-reboot
120   (qemu) migrate_set_capability x-ignore-shared on
121   (qemu) migrate -d file:vm.state
122   (qemu) info status
124   (qemu) quit
131   # qemu-kvm ... -incoming defer
132   (qemu) info status
134   (qemu) migrate_set_parameter mode cpr-reboot
135   (qemu) migrate_set_capability x-ignore-shared on
136   (qemu) migrate_incoming file:vm.state
137   (qemu) info status
139   (qemu) system_wakeup
140   (qemu) info status
152 This mode allows the user to transfer a guest to a new QEMU instance
154 RAM in place, albeit with new virtual addresses in new QEMU.  Devices
155 and their pinned memory pages will also be preserved in a future QEMU
158 The user starts new QEMU on the same host as old QEMU, with command-
165 To initiate CPR, the user issues a migrate command to old QEMU,
167 argument.  Old QEMU stops the VM, saves state to the migration
169 new QEMU.
171 New QEMU reads the CPR channel before opening a monitor, hence
192   * Start new QEMU with two ``-incoming`` options.
194     issued, then QEMU automatically resumes VM execution.
210 old QEMU before issuing any monitor commands to new QEMU, because new
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
213 command is issued.  However, new QEMU does not open and read the
219 In these examples, we simply restart the same version of QEMU, but
220 in a real scenario one would start new QEMU on the incoming side.
221 Note that new QEMU does not print the monitor prompt until old QEMU
230   # qemu-kvm -qmp stdio
236                                         # qemu-kvm -monitor stdio
259                                         QEMU 10.0.50 monitor
260                                         (qemu) info status
272 migrate command to old QEMU before you can issue any monitor
273 commands to new QEMU.
280   # qemu-kvm -monitor stdio
286                                         # qemu-kvm -monitor stdio
308                                         QEMU 10.0.50 monitor
309                                         (qemu) info status
311                                         (qemu) device_add pcie-root-port
312                                         (qemu) migrate_incoming tcp:0:44444
313                                         (qemu) info status
324 descriptors from old to new QEMU.  In the future, descriptors for