Re: [PATCH V1 4/4] cpr: reboot mode

[Juan Quintela]

Steve Sistare <steven.sistare@oracle.com> wrote:
> 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.

Please, add this message to doc/<somewhere> instead (or additionally) to
the commit log.

> 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:

It only works with file backend, and we don't have any check for that.
Wondering how to add that check.

Additionally, you are not adding a migration test that does exactly what
you put there in the comment.

Thanks, Juan.