[RFC 5/6] migration: Deprecate block migration

[Juan Quintela]

It is obsolete.  It is better to use driver_mirror+NBD instead.

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>

---

Can any of you give one example of how to use driver_mirror+NBD for
deprecated.rst?

Thanks, Juan.
---
 docs/about/deprecated.rst |  6 ++++++
 qapi/migration.json       | 29 +++++++++++++++++++++++++----
 migration/block.c         |  2 ++
 migration/options.c       |  7 +++++++
 4 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 518672722d..173c5ba5cb 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -454,3 +454,9 @@ Everything except ``-incoming defer`` are deprecated.  This 
allows to
 setup parameters before launching the proper migration with
 ``migrate-incoming uri``.
 
+block migration (since 8.1)
+'''''''''''''''''''''''''''
+
+Block migration is too inflexible.  It needs to migrate all block
+devices or none.  Use driver_mirror+NBD instead.
+
diff --git a/qapi/migration.json b/qapi/migration.json
index b71e00737e..a8497de48d 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -258,11 +258,16 @@
 #     blocked.  Present and non-empty when migration is blocked.
 #     (since 6.0)
 #
+# Features:
+#
+# @deprecated: @disk migration is deprecated.  Use driver_mirror+NBD
+#     instead.
+#
 # 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',
@@ -497,6 +502,9 @@
 #
 # Features:
 #
+# @deprecated: @block migration is deprecated.  Use driver_mirror+NBD
+#     instead.
+#
 # @unstable: Members @x-colo and @x-ignore-shared are experimental.
 #
 # Since: 1.2
@@ -506,7 +514,8 @@
            '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',
@@ -789,6 +798,9 @@
 #
 # Features:
 #
+# @deprecated: Member @block-incremental is obsolete. Use
+#     driver_mirror+NBD instead.
+#
 # @unstable: Member @x-checkpoint-delay is experimental.
 #
 # Since: 2.4
@@ -803,7 +815,7 @@
            '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',
@@ -945,6 +957,9 @@
 #
 # Features:
 #
+# @deprecated: Member @block-incremental is obsolete. Use
+#     driver_mirror+NBD instead.
+#
 # @unstable: Member @x-checkpoint-delay is experimental.
 #
 # TODO: either fuse back into MigrationParameters, or make
@@ -972,7 +987,8 @@
             '*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',
@@ -1137,6 +1153,9 @@
 #
 # Features:
 #
+# @deprecated: Member @block-incremental is obsolete. Use
+#     driver_mirror+NBD instead.
+#
 # @unstable: Member @x-checkpoint-delay is experimental.
 #
 # Since: 2.4
@@ -1161,6 +1180,8 @@
             '*downtime-limit': 'uint64',
             '*x-checkpoint-delay': { 'type': 'uint32',
                                      'features': [ 'unstable' ] },
+            '*block-incremental': { 'type': 'bool',
+                                    'features': [ 'deprecated' ] },
             '*block-incremental': 'bool',
             '*multifd-channels': 'uint8',
             '*xbzrle-cache-size': 'size',
diff --git a/migration/block.c b/migration/block.c
index b9580a6c7e..2521a22269 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -722,6 +722,8 @@ 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 mirror jobs instead.");
+
     qemu_mutex_lock_iothread();
     ret = init_blk_migration(f);
     if (ret < 0) {
diff --git a/migration/options.c b/migration/options.c
index b62ab30cd5..374dc0767e 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"
@@ -437,6 +438,10 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, 
Error **errp)
         return false;
     }
 #endif
+    if (new_caps[MIGRATION_CAPABILITY_BLOCK]) {
+        warn_report("Block migration is deprecated. "
+                    "Use driver_mirror+NBD instead.");
+    }
 
 #ifndef CONFIG_REPLICATION
     if (new_caps[MIGRATION_CAPABILITY_X_COLO]) {
@@ -1257,6 +1262,8 @@ static void migrate_params_apply(MigrateSetParameters 
*params, Error **errp)
     }
 
     if (params->has_block_incremental) {
+        warn_report("Block migration is deprecated. "
+                    "Use driver_mirror+NBD instead.");
         s->parameters.block_incremental = params->block_incremental;
     }
     if (params->has_multifd_channels) {
-- 
2.40.1