Re: [PATCH v3 3/4] migration: Deprecate block migration

[Markus Armbruster <armbru@redhat.com>]

Juan Quintela <quintela@redhat.com> writes:

> It is obsolete.  It is better to use driver-mirror with NBD instead.

drive-mirror

Several more below.

>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Hanna Czenczek <hreitz@redhat.com>
>
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  docs/about/deprecated.rst | 10 ++++++++++
>  qapi/migration.json       | 30 +++++++++++++++++++++++++-----
>  migration/block.c         |  3 +++
>  migration/options.c       |  9 ++++++++-
>  4 files changed, 46 insertions(+), 6 deletions(-)
>
> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> index b2b7e11742..e46f3df376 100644
> --- a/docs/about/deprecated.rst
> +++ b/docs/about/deprecated.rst
> @@ -431,3 +431,13 @@ The new way to modify migration is using migration parameters.
>  ``blk`` functionality can be achieved by setting the
>  ``block`` migration capability to ``true``.
>  
> +block migration (since 8.2)
> +'''''''''''''''''''''''''''
> +
> +Block migration is too inflexible.  It needs to migrate all block
> +devices or none.
> +
> +Please see "QMP invocation for live storage migration with
> +``driver-mirror`` + NBD" in docs/interop/live-block-operations.rst for
> +a detailed explanation.
> +
> diff --git a/qapi/migration.json b/qapi/migration.json
> index e4949e0d8e..bf6e1ac5b5 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -269,11 +269,16 @@
>  #     average memory load of the virtual CPU indirectly.  Note that
>  #     zero means guest doesn't dirty memory.  (Since 8.1)
>  #
> +# Features:
> +#
> +# @deprecated: @disk migration is deprecated.  Use driver-mirror
> +#     with NBD instead.
> +#

Suggest:

   # @deprecated: Member @disk is deprecated because block migration is.

>  # Since: 0.14
>  ##
>  { 'struct': 'MigrationInfo',
>    'data': {'*status': 'MigrationStatus', '*ram': 'MigrationStats',
> -           '*disk': 'MigrationStats',
> +           '*disk': { 'type': 'MigrationStats', 'features': ['deprecated'] },
>             '*vfio': 'VfioStats',
>             '*xbzrle-cache': 'XBZRLECacheStats',
>             '*total-time': 'int',
> @@ -526,6 +531,9 @@
>  #
>  # Features:
>  #
> +# @deprecated: @block migration is deprecated.  Use driver-mirror
> +#     with NBD instead.
> +#

Suggest:

   # @deprecated: Member @block is deprecated.  Use drrive-mirror with
   # NBD instead.

>  # @unstable: Members @x-colo and @x-ignore-shared are experimental.
>  #
>  # Since: 1.2
> @@ -535,7 +543,8 @@
>             'compress', 'events', 'postcopy-ram',
>             { 'name': 'x-colo', 'features': [ 'unstable' ] },
>             'release-ram',
> -           'block', 'return-path', 'pause-before-switchover', 'multifd',
> +           { 'name': 'block', 'features': [ 'deprecated' ] },
> +           'return-path', 'pause-before-switchover', 'multifd',
>             'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
>             { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
>             'validate-uuid', 'background-snapshot',
> @@ -826,6 +835,9 @@
>  #
>  # Features:
>  #
> +# @deprecated: Member @block-incremental is obsolete. Use
> +#     driver-mirror with NBD instead.
> +#

Wait!  This is what PATCH 1 tells users to use instead of deprecated
@inc.  You need to update that deprecation note to point to a
non-deprecated replacement.

>  # @unstable: Members @x-checkpoint-delay and @x-vcpu-dirty-limit-period
>  #     are experimental.
>  #
> @@ -841,7 +853,7 @@
>             'tls-creds', 'tls-hostname', 'tls-authz', 'max-bandwidth',
>             'downtime-limit',
>             { 'name': 'x-checkpoint-delay', 'features': [ 'unstable' ] },
> -           'block-incremental',
> +           { 'name': 'block-incremental', 'features': [ 'deprecated' ] },
>             'multifd-channels',
>             'xbzrle-cache-size', 'max-postcopy-bandwidth',
>             'max-cpu-throttle', 'multifd-compression',
> @@ -992,6 +1004,9 @@
>  #
>  # Features:
>  #
> +# @deprecated: Member @block-incremental is obsolete. Use
> +#     driver-mirror with NBD instead.
> +#
>  # @unstable: Members @x-checkpoint-delay and @x-vcpu-dirty-limit-period
>  #     are experimental.
>  #
> @@ -1020,7 +1035,8 @@
>              '*downtime-limit': 'uint64',
>              '*x-checkpoint-delay': { 'type': 'uint32',
>                                       'features': [ 'unstable' ] },
> -            '*block-incremental': 'bool',
> +            '*block-incremental': { 'type': 'bool',
> +                                    'features': [ 'deprecated' ] },
>              '*multifd-channels': 'uint8',
>              '*xbzrle-cache-size': 'size',
>              '*max-postcopy-bandwidth': 'size',
> @@ -1195,6 +1211,9 @@
>  #
>  # Features:
>  #
> +# @deprecated: Member @block-incremental is obsolete. Use
> +#     driver-mirror with NBD instead.
> +#
>  # @unstable: Members @x-checkpoint-delay and @x-vcpu-dirty-limit-period
>  #     are experimental.
>  #
> @@ -1220,7 +1239,8 @@
>              '*downtime-limit': 'uint64',
>              '*x-checkpoint-delay': { 'type': 'uint32',
>                                       'features': [ 'unstable' ] },
> -            '*block-incremental': 'bool',
> +            '*block-incremental': { 'type': 'bool',
> +                                    'features': [ 'deprecated' ] },
>              '*multifd-channels': 'uint8',
>              '*xbzrle-cache-size': 'size',
>              '*max-postcopy-bandwidth': 'size',
> diff --git a/migration/block.c b/migration/block.c
> index 5f930870a5..46bb431ed3 100644
> --- a/migration/block.c
> +++ b/migration/block.c
> @@ -729,6 +729,9 @@ static int block_save_setup(QEMUFile *f, void *opaque)
>      trace_migration_block_save("setup", block_mig_state.submitted,
>                                 block_mig_state.transferred);
>  
> +    warn_report("block migration is deprecated.  Use driver-mirror with"
> +                "NBD instead.");
> +
>      qemu_mutex_lock_iothread();
>      ret = init_blk_migration(f);
>      if (ret < 0) {
> diff --git a/migration/options.c b/migration/options.c
> index 6bbfd4853d..48cbbd682a 100644
> --- a/migration/options.c
> +++ b/migration/options.c
> @@ -12,6 +12,7 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include "qemu/error-report.h"
>  #include "exec/target_page.h"
>  #include "qapi/clone-visitor.h"
>  #include "qapi/error.h"
> @@ -464,10 +465,14 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
>      if (new_caps[MIGRATION_CAPABILITY_BLOCK]) {
>          error_setg(errp, "QEMU compiled without old-style (blk/-b, inc/-i) "
>                     "block migration");
> -        error_append_hint(errp, "Use drive_mirror+NBD instead.\n");
> +        error_append_hint(errp, "Use driver-mirror with NBD instead.\n");
>          return false;
>      }
>  #endif
> +    if (new_caps[MIGRATION_CAPABILITY_BLOCK]) {
> +        warn_report("Block migration is deprecated. "
> +                    "Use driver-mirror with NBD instead.");
> +    }
>  
>  #ifndef CONFIG_REPLICATION
>      if (new_caps[MIGRATION_CAPABILITY_X_COLO]) {
> @@ -1351,6 +1356,8 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
>      }
>  
>      if (params->has_block_incremental) {
> +        warn_report("Block migration is deprecated. "
> +                    "Use driver-mirror with NBD instead.");
>          s->parameters.block_incremental = params->block_incremental;
>      }
>      if (params->has_multifd_channels) {