[PATCH V2 0/6] Live Update reboot mode

[Steve Sistare <steven.sistare@oracle.com>]

Add a mode migration parameter that can be used to select alternate
migration algorithms.  The default mode is normal, representing the
current migration algorithm, and does not need to be explicitly set.

Provide the cpr-reboot (CheckPoint and Restart) migration mode for live
update, which saves state to a file.  This allows one to quit qemu, reboot
to an updated kernel, install an updated version of qemu, and resume via
the migrate-incoming command.  The caller must specify a migration URI
that writes to and reads from a file, and must set the mode parameter
before invoking the migrate or migrate-incoming commands.

Unlike normal mode, the use of certain local storage options does not block
cpr-reboot mode, but the caller must not modify guest block devices between
the quit and restart.  To avoid saving guest RAM to the state file, the memory
backend must be shared, and the @x-ignore-shared migration capability must
be set.

Guest RAM must be non-volatile across reboot, which can be achieved by
backing it with a dax device, or /dev/shm PKRAM as proposed in
https://lore.kernel.org/lkml/1617140178-8773-1-git-send-email-anthony.yznaga@oracle.com
but this is not enforced.  The restarted qemu arguments must match those used
to initially start qemu, plus the -incoming option.

This patch series contains minimal functionality.  Future patches will enhance
reboot mode by preserving vfio devices for suspended guests.  They will also
add a new mode for updating qemu using the exec system call, which will keep
vfio devices and certain character devices alive.

Here is an example of updating the host kernel using reboot mode.

window 1                                        | window 2
                                                |
# qemu-system-$arch -monitor stdio              |
  mem-path=/dev/dax0.0 ...                      |
QEMU 8.1.50 monitor - type 'help' for more info |
(qemu) info status                              |
VM status: running                              |
                                                | # yum update kernel-uek
(qemu) migrate_set_capability x-ignore-shared on|
(qemu) migrate_set_parameter mode cpr-reboot    |
(qemu) migrate -d file:vm.state                 |
(qemu) info status                              |
VM status: paused (postmigrate)                 |
(qemu) quit                                     |
                                                |
# systemctl kexec                               |
kexec_core: Starting new kernel                 |
...                                             |
                                                |
# qemu-system-$arch -monitor stdio              |
  mem-path=/dev/dax0.0 -incoming defer ...      |
QEMU 8.1.50 monitor - type 'help' for more info |
(qemu) info status                              |
VM status: paused (inmigrate)                   |
(qemu) migrate_set_capability x-ignore-shared on|
(qemu) migrate_set_parameter mode cpr-reboot    |
(qemu) migrate_incoming file:vm.state           |
(qemu) info status                              |
VM status: running                              |

Changes in V2:
  - moved "migration mode" code and comments to more appropriate places
  - clarified the behavior of non-shared-memory backends
  - split blocker patches and reverted some blockers
  - added a test

Steve Sistare (6):
  migration: mode parameter
  migration: per-mode blockers
  cpr: relax blockdev migration blockers
  cpr: relax vhost migration blockers
  cpr: reboot mode
  tests/qtest: migration: add reboot mode test

 block/parallels.c                   |  2 +-
 block/qcow.c                        |  2 +-
 block/vdi.c                         |  2 +-
 block/vhdx.c                        |  2 +-
 block/vmdk.c                        |  2 +-
 block/vpc.c                         |  2 +-
 block/vvfat.c                       |  2 +-
 hw/core/qdev-properties-system.c    | 14 ++++++
 hw/scsi/vhost-scsi.c                |  2 +-
 hw/virtio/vhost.c                   |  2 +-
 include/hw/qdev-properties-system.h |  4 ++
 include/migration/blocker.h         | 44 +++++++++++++++--
 include/migration/misc.h            |  1 +
 migration/migration-hmp-cmds.c      |  9 ++++
 migration/migration.c               | 95 ++++++++++++++++++++++++++++++++-----
 migration/options.c                 | 21 ++++++++
 migration/options.h                 |  1 +
 qapi/migration.json                 | 40 ++++++++++++++--
 stubs/migr-blocker.c                | 10 ++++
 tests/qtest/migration-test.c        | 27 +++++++++++
 20 files changed, 255 insertions(+), 29 deletions(-)

-- 
1.8.3.1