Re: [PATCH v4 03/10] migration: migrate 'inc' command option is deprecated.

[Markus Armbruster <armbru@redhat.com>]

Juan Quintela <quintela@redhat.com> writes:

> Set the 'block_incremental' migration parameter to 'true' instead.
>
> Reviewed-by: Thomas Huth <thuth@redhat.com>
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Juan Quintela <quintela@redhat.com>
>
> ---
>
> Improve documentation and style (thanks Markus)
> ---
>  docs/about/deprecated.rst | 7 +++++++
>  qapi/migration.json       | 8 +++++++-
>  migration/migration.c     | 6 ++++++
>  3 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> index 1c4d7f36f0..1b6b2870cf 100644
> --- a/docs/about/deprecated.rst
> +++ b/docs/about/deprecated.rst
> @@ -452,3 +452,10 @@ Migration
>  ``skipped`` field in Migration stats has been deprecated.  It hasn't
>  been used for more than 10 years.
>  
> +``inc`` migrate command option (since 8.2)
> +''''''''''''''''''''''''''''''''''''''''''
> +
> +The new way to modify migration is using migration parameters.
> +``inc`` functionality can be achieved by setting the
> +``block-incremental`` migration parameter to ``true``.
> +
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 6865fea3c5..56bbd55b87 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -1492,6 +1492,11 @@
>  #
>  # @resume: resume one paused migration, default "off". (since 3.0)
>  #
> +# Features:
> +#
> +# @deprecated: Member @inc is deprecated.  Use migration parameter
> +#     @block-incremental instead.

This is fine now.  It becomes bad advice in PATCH 05, which deprecates
@block-incremental.  Two solutions:

1. Change this patch to point to an alternative that will *not* be
deprecated.

2. Change PATCH 05.

Same end result.

> +#
>  # Returns: nothing on success
>  #
>  # Since: 0.14
> @@ -1513,7 +1518,8 @@
>  # <- { "return": {} }
>  ##
>  { 'command': 'migrate',
> -  'data': {'uri': 'str', '*blk': 'bool', '*inc': 'bool',
> +  'data': {'uri': 'str', '*blk': 'bool',
> +           '*inc': { 'type': 'bool', 'features': [ 'deprecated' ] },
>             '*detach': 'bool', '*resume': 'bool' } }
>  
>  ##
> diff --git a/migration/migration.c b/migration/migration.c
> index 1c6c81ad49..ac4897fe0d 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1601,6 +1601,12 @@ static bool migrate_prepare(MigrationState *s, bool blk, bool blk_inc,
>  {
>      Error *local_err = NULL;
>  
> +    if (blk_inc) {
> +        warn_report("@inc/-i migrate option is deprecated, set the"

This is either about QMP migrate's parameter "inc", or HMP migrate's
flags -i.

In the former case, we want something like "parameter 'inc' is
deprecated".

In the latter case, we want something like "-i is deprecated".

Trying to do both in a single message results in a sub-par message.  If
you want to do better, you have to check in hmp_migrate(), too.  Then
hmp_migrate can refer to "-i", and migrate_prepare() to "parameter
'inc'".  Up to you.

If you decide a single message is good enough, use something like
"parameter 'inc' / flag -i is deprecated".

> +                    "'block-incremental' migration parameter to 'true'"
> +                    " instead.");

Again, fine now, becomes bad advice in PATCH 05.

> +    }
> +
>      if (resume) {
>          if (s->state != MIGRATION_STATUS_POSTCOPY_PAUSED) {
>              error_setg(errp, "Cannot resume if there is no "