[PATCH V1 4/4] cpr: reboot mode

[Steve Sistare]

Add the cpr-reboot migration mode.  Usage:

$ qemu-system-$arch -monitor stdio ...
QEMU 8.1.50 monitor - type 'help' for more information
(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

$ qemu-system-$arch -monitor stdio -incoming defer ...
QEMU 8.1.50 monitor - type 'help' for more information
(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

In this mode, the migrate command saves state to a file, allowing one
to quit qemu, reboot to an updated kernel, and restart an updated version
of qemu.  The caller must specify a migration URI that writes to and reads
from a file.  Unlike normal mode, the use of certain local storage options
does not block the migration, but the caller must not modify guest block
devices between the quit and restart.  The guest RAM memory-backend must
be shared, and the @x-ignore-shared migration capability must be set,
to avoid saving RAM to the file.  Guest RAM must be non-volatile across
reboot, such as by backing it with a dax device, but this is not enforced.
The restarted qemu arguments must match those used to initially start qemu,
plus the -incoming option.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 qapi/migration.json | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index 184fb78..2d862fa 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -620,9 +620,23 @@
 #
 # @normal: the original form of migration. (since 8.2)
 #
+# @cpr-reboot: The migrate command saves state to a file, allowing one to
+#              quit qemu, reboot to an updated kernel, and restart an updated
+#              version of qemu.  The caller must specify a migration URI
+#              that writes to and reads from a file.  Unlike normal mode,
+#              the use of certain local storage options does not block the
+#              migration, but the caller must not modify guest block devices
+#              between the quit and restart.  The guest RAM memory-backend
+#              must be shared, and the @x-ignore-shared migration capability
+#              must be set, to avoid saving it to the file.  Guest RAM must
+#              be non-volatile across reboot, such as by backing it with
+#              a dax device, but this is not enforced.  The restarted qemu
+#              arguments must match those used to initially start qemu, plus
+#              the -incoming option. (since 8.2)
+#
 ##
 { 'enum': 'MigMode',
-  'data': [ 'normal' ] }
+  'data': [ 'normal', 'cpr-reboot' ] }
 
 ##
 # @BitmapMigrationBitmapAliasTransform:
-- 
1.8.3.1