Re: [PATCH v2] migration: Drop redundant query-migrate result @blocked

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Markus Armbruster <armbru@redhat.com>
Cc: peter.maydell@linaro.org, qemu-devel@nongnu.org,
	peterx@redhat.com, dgilbert@redhat.com
Subject: Re: [PATCH v2] migration: Drop redundant query-migrate result @blocked
Date: Tue, 20 Apr 2021 09:35:23 +0100	[thread overview]
Message-ID: <YH6SS7gm3Ic6T49h@redhat.com> (raw)
In-Reply-To: <20210420051907.891470-2-armbru@redhat.com>

On Tue, Apr 20, 2021 at 07:19:07AM +0200, Markus Armbruster wrote:
> Result @blocked is true when and only when result @blocked-reasons is
> present.  It's always non-empty when present.  @blocked is redundant.
> It was introduced in commit 3af8554bd0 "migration: Add blocker
> information", and has not been released.  This gives us a chance to
> fix the interface with minimal fuss: drop @blocked.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
> This is alternative to "[PATCH] migration: Deprecate redundant
> query-migrate result @blocked".
> 
>  qapi/migration.json   |  7 +++----
>  migration/migration.c | 29 +++++++++++++----------------
>  monitor/hmp-cmds.c    |  2 +-
>  3 files changed, 17 insertions(+), 21 deletions(-)
> 
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 9bf0bc4d25..7a5bdf9a0d 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -224,9 +224,9 @@
>  #        only returned if VFIO device is present, migration is supported by all
>  #        VFIO devices and status is 'active' or 'completed' (since 5.2)
>  #
> -# @blocked: True if outgoing migration is blocked (since 6.0)
> -#
> -# @blocked-reasons: A list of reasons an outgoing migration is blocked (since 6.0)
> +# @blocked-reasons: A list of reasons an outgoing migration is blocked.
> +#                   Present and non-empty when migration is blocked.
> +#                   (since 6.0)
>  #
>  # Since: 0.14
>  ##
> @@ -241,7 +241,6 @@
>             '*setup-time': 'int',
>             '*cpu-throttle-percentage': 'int',
>             '*error-desc': 'str',
> -           'blocked': 'bool',
>             '*blocked-reasons': ['str'],
>             '*postcopy-blocktime' : 'uint32',
>             '*postcopy-vcpu-blocktime': ['uint32'],
> diff --git a/migration/migration.c b/migration/migration.c
> index 8ca034136b..fdadee290e 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1073,27 +1073,24 @@ static void populate_vfio_info(MigrationInfo *info)
>  static void fill_source_migration_info(MigrationInfo *info)
>  {
>      MigrationState *s = migrate_get_current();
> +    GSList *cur_blocker = migration_blockers;
>  
> -    info->blocked = migration_is_blocked(NULL);

So migration_is_blocked() method returns true if either of the
following conditions is met

 - qemu_savevm_state_blocked  returns true - this happens
   if a savevm state handler has 'unmigratable' flag set

 - if any migration blockers are registered.

We're then calling qemu_savevm_non_migratable_list to populate
blocked_reasons  based on "unmigratable" flag, and then further
populate blocked_reasons based on migration blockers.

So I agree it is functionally the same result old and new code.

> -    info->has_blocked_reasons = info->blocked;
>      info->blocked_reasons = NULL;
> -    if (info->blocked) {
> -        GSList *cur_blocker = migration_blockers;
>  
> -        /*
> -         * There are two types of reasons a migration might be blocked;
> -         * a) devices marked in VMState as non-migratable, and
> -         * b) Explicit migration blockers
> -         * We need to add both of them here.
> -         */
> -        qemu_savevm_non_migratable_list(&info->blocked_reasons);
> +    /*
> +     * There are two types of reasons a migration might be blocked;
> +     * a) devices marked in VMState as non-migratable, and
> +     * b) Explicit migration blockers
> +     * We need to add both of them here.
> +     */
> +    qemu_savevm_non_migratable_list(&info->blocked_reasons);
>  
> -        while (cur_blocker) {
> -            QAPI_LIST_PREPEND(info->blocked_reasons,
> -                              g_strdup(error_get_pretty(cur_blocker->data)));
> -            cur_blocker = g_slist_next(cur_blocker);
> -        }
> +    while (cur_blocker) {
> +        QAPI_LIST_PREPEND(info->blocked_reasons,
> +                          g_strdup(error_get_pretty(cur_blocker->data)));
> +        cur_blocker = g_slist_next(cur_blocker);
>      }
> +    info->has_blocked_reasons = info->blocked_reasons != NULL;
>  
>      switch (s->state) {
>      case MIGRATION_STATUS_NONE:

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Regards,
Daniel
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