Re: [PATCH 4/6] migration: Add ram-only capability

[Vladimir Sementsov-Ogievskiy]

24.12.2021 14:11, Nikita Lapshin wrote:
> If this capability is enabled migration stream
> will have RAM section only.
>
> Signed-off-by: Nikita Lapshin <nikita.lapshin@virtuozzo.com>
> ---
>   migration/migration.c | 20 +++++++++++++++++++-
>   migration/migration.h |  1 +
>   migration/savevm.c    | 11 ++++++++++-
>   qapi/migration.json   |  7 +++++--
>   4 files changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/migration/migration.c b/migration/migration.c
> index 006447d00a..4d7ef9d8dc 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1257,6 +1257,14 @@ static bool migrate_caps_check(bool *cap_list,
>           return false;
>       }
>   
> +    if (cap_list[MIGRATION_CAPABILITY_NO_RAM] &&
> +        cap_list[MIGRATION_CAPABILITY_RAM_ONLY]) {
> +        error_setg(errp, "ram-only and no-ram aren't "
> +                         "compatible with each other");
> +
> +        return false;
> +    }
> +
>       return true;
>   }
>   
> @@ -2619,6 +2627,15 @@ bool migrate_no_ram(void)
>       return s->enabled_capabilities[MIGRATION_CAPABILITY_NO_RAM];
>   }
>   
> +bool migrate_ram_only(void)
> +{
> +    MigrationState *s;
> +
> +    s = migrate_get_current();
> +
> +    return s->enabled_capabilities[MIGRATION_CAPABILITY_RAM_ONLY];
> +}
> +
>   /* migration thread support */
>   /*
>    * Something bad happened to the RP stream, mark an error
> @@ -3973,7 +3990,8 @@ static void *bg_migration_thread(void *opaque)
>        * save their state to channel-buffer along with devices.
>        */
>       cpu_synchronize_all_states();
> -    if (qemu_savevm_state_complete_precopy_non_iterable(fb, false, false)) {
> +    if (!migrate_ram_only() &&
> +        qemu_savevm_state_complete_precopy_non_iterable(fb, false, false)) {

Here... [*]

>           goto fail;
>       }
>       /*
> diff --git a/migration/migration.h b/migration/migration.h
> index 43f7bf8eba..d5a077e00d 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -359,6 +359,7 @@ bool migrate_use_events(void);
>   bool migrate_postcopy_blocktime(void);
>   bool migrate_background_snapshot(void);
>   bool migrate_no_ram(void);
> +bool migrate_ram_only(void);
>   
>   /* Sending on the return path - generic and then for each message type */
>   void migrate_send_rp_shut(MigrationIncomingState *mis,
> diff --git a/migration/savevm.c b/migration/savevm.c
> index ba644083ab..e41ca76000 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -249,6 +249,7 @@ typedef struct SaveStateEntry {
>       void *opaque;
>       CompatEntry *compat;
>       int is_iterable;
> +    bool is_ram;
>   } SaveStateEntry;
>   
>   typedef struct SaveState {
> @@ -802,6 +803,10 @@ int register_savevm_live(const char *idstr,
>           se->is_iterable = 1;
>       }
>   
> +    if (!strcmp("ram", idstr)) {
> +        se->is_ram = true;
> +    }
> +
>       pstrcat(se->idstr, sizeof(se->idstr), idstr);
>   
>       if (instance_id == VMSTATE_INSTANCE_ID_ANY) {
> @@ -949,6 +954,10 @@ static bool should_skip(SaveStateEntry *se)
>           return true;
>       }
>   
> +    if (migrate_ram_only() && !se->is_ram) {
> +        return true;
> +    }
> +
>       return false;
>   }
>   
> @@ -1486,7 +1495,7 @@ int qemu_savevm_state_complete_precopy(QEMUFile *f, bool iterable_only,
>           }
>       }
>   
> -    if (iterable_only) {
> +    if (iterable_only || migrate_ram_only()) {
>           goto flush;
>       }

[*] ... and here you care to avoid calling same 
qemu_savevm_state_complete_precopy_non_iterable()

Seems better to check migrate_ram_only at start of 
qemu_savevm_state_complete_precopy_non_iterable() and do early return from it.

>   
> diff --git a/qapi/migration.json b/qapi/migration.json
> index d53956852c..626fc59d14 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -454,6 +454,8 @@
>   #
>   # @no-ram: If enabled, migration stream won't contain any ram in it. (since 
> 7.0)
>   #
> +# @ram-only: If enabled, only RAM sections will be sent. (since 7.0)
> +#
>   # Features:
>   # @unstable: Members @x-colo and @x-ignore-shared are experimental.
>   #
> @@ -467,7 +469,7 @@
>              'block', 'return-path', 'pause-before-switchover', 'multifd',
>              'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
>              { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
> -           'validate-uuid', 'background-snapshot', 'no-ram'] }
> +           'validate-uuid', 'background-snapshot', 'no-ram', 'ram-only'] }
>   ##
>   # @MigrationCapabilityStatus:
>   #
> @@ -521,7 +523,8 @@
>   #       {"state": true, "capability": "events"},
>   #       {"state": false, "capability": "postcopy-ram"},
>   #       {"state": false, "capability": "x-colo"},
> -#       {"state": false, "capability": "no-ram"}
> +#       {"state": false, "capability": "no-ram"},
> +#       {"state": false, "capability": "ram-only"}
>   #    ]}
>   #
>   ##


--
Best regards,
Vladimir