From: Fabiano Rosas <farosas@suse.de>

The zero-blocks capability was meant to be used along with the block
migration, which has been removed already in commit eef0bae3a7
("migration: Remove block migration").

Setting zero-blocks is currently a noop, but the outright removal of
the capability would cause and error in case some users are still
setting it. Put the capability through the deprecation process.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240919134626.166183-4-dave@treblig.org
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 docs/about/deprecated.rst | 6 ++++++
 qapi/migration.json       | 5 ++++-
 migration/options.c       | 4 ++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index c02bbb66f7..33ce4f9536 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -467,3 +467,9 @@ usage of providing a file descriptor to a plain file has been
 deprecated in favor of explicitly using the ``file:`` URI with the
 file descriptor being passed as an ``fdset``. Refer to the ``add-fd``
 command documentation for details on the ``fdset`` usage.
+
+``zero-blocks`` capability (since 9.2)
+''''''''''''''''''''''''''''''''''''''
+
+The ``zero-blocks`` capability was part of the block migration which
+doesn't exist anymore since it was removed in QEMU v9.1.
diff --git a/qapi/migration.json b/qapi/migration.json
index b66cccf107..3af6aa1740 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -479,11 +479,14 @@
 # Features:
 #
 # @unstable: Members @x-colo and @x-ignore-shared are experimental.
+# @deprecated: Member @zero-blocks is deprecated as being part of
+#     block migration which was already removed.
 #
 # Since: 1.2
 ##
 { 'enum': 'MigrationCapability',
-  'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks',
+  'data': ['xbzrle', 'rdma-pin-all', 'auto-converge',
+           { 'name': 'zero-blocks', 'features': [ 'deprecated' ] },
            'events', 'postcopy-ram',
            { 'name': 'x-colo', 'features': [ 'unstable' ] },
            'release-ram',
diff --git a/migration/options.c b/migration/options.c
index 6f549984cb..ad8d6989a8 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -450,6 +450,10 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp)
     ERRP_GUARD();
     MigrationIncomingState *mis = migration_incoming_get_current();
 
+    if (new_caps[MIGRATION_CAPABILITY_ZERO_BLOCKS]) {
+        warn_report("zero-blocks capability is deprecated");
+    }
+
 #ifndef CONFIG_REPLICATION
     if (new_caps[MIGRATION_CAPABILITY_X_COLO]) {
         error_setg(errp, "QEMU compiled without replication module"
-- 
2.45.0