[PATCH v2 08/11] multifd: Add capability to enable/disable zero_page

[Juan Quintela <quintela@redhat.com>]

We have to enable it by default until we introduce the new code.

Signed-off-by: Juan Quintela <quintela@redhat.com>

---

Change it to a capability.  As capabilities are off by default, have
to change MULTIFD_ZERO_PAGE to MAIN_ZERO_PAGE, so it is false for
default, and true for older versions.
---
 qapi/migration.json   |  8 +++++++-
 migration/migration.h |  1 +
 hw/core/machine.c     |  1 +
 migration/migration.c | 13 ++++++++++++-
 4 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index 88ecf86ac8..ac5bc071a9 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -472,12 +472,18 @@
 #                  Requires that QEMU be permitted to use locked memory
 #                  for guest RAM pages.
 #                  (since 7.1)
+#
 # @postcopy-preempt: If enabled, the migration process will allow postcopy
 #                    requests to preempt precopy stream, so postcopy requests
 #                    will be handled faster.  This is a performance feature and
 #                    should not affect the correctness of postcopy migration.
 #                    (since 7.1)
 #
+# @main-zero-page: If enabled, the detection of zero pages will be
+#                  done on the main thread.  Otherwise it is done on
+#                  the multifd threads.
+#                  (since 8.0)
+#
 # Features:
 # @unstable: Members @x-colo and @x-ignore-shared are experimental.
 #
@@ -492,7 +498,7 @@
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
            { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
            'validate-uuid', 'background-snapshot',
-           'zero-copy-send', 'postcopy-preempt'] }
+           'zero-copy-send', 'postcopy-preempt', 'main-zero-page'] }
 
 ##
 # @MigrationCapabilityStatus:
diff --git a/migration/migration.h b/migration/migration.h
index ae4ffd3454..c38a0baf10 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -408,6 +408,7 @@ int migrate_multifd_channels(void);
 MultiFDCompression migrate_multifd_compression(void);
 int migrate_multifd_zlib_level(void);
 int migrate_multifd_zstd_level(void);
+bool migrate_use_main_zero_page(void);
 
 #ifdef CONFIG_LINUX
 bool migrate_use_zero_copy_send(void);
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 616f3a207c..97149e2de3 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -52,6 +52,7 @@ const size_t hw_compat_7_1_len = G_N_ELEMENTS(hw_compat_7_1);
 GlobalProperty hw_compat_7_0[] = {
     { "arm-gicv3-common", "force-8-bit-prio", "on" },
     { "nvme-ns", "eui64-default", "on"},
+    { "migration", "main-zero-page", "true" },
 };
 const size_t hw_compat_7_0_len = G_N_ELEMENTS(hw_compat_7_0);
 
diff --git a/migration/migration.c b/migration/migration.c
index d261c7d16d..ab86c6601d 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -164,7 +164,8 @@ INITIALIZE_MIGRATE_CAPS_SET(check_caps_background_snapshot,
     MIGRATION_CAPABILITY_XBZRLE,
     MIGRATION_CAPABILITY_X_COLO,
     MIGRATION_CAPABILITY_VALIDATE_UUID,
-    MIGRATION_CAPABILITY_ZERO_COPY_SEND);
+    MIGRATION_CAPABILITY_ZERO_COPY_SEND,
+    MIGRATION_CAPABILITY_MAIN_ZERO_PAGE);
 
 /* When we add fault tolerance, we could have several
    migrations at once.  For now we don't need to add
@@ -2603,6 +2604,14 @@ bool migrate_use_multifd(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD];
 }
 
+bool migrate_use_main_zero_page(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    /* We will enable this when we add the right code. */
+    return true || s->enabled_capabilities[MIGRATION_CAPABILITY_MAIN_ZERO_PAGE];
+}
+
 bool migrate_pause_before_switchover(void)
 {
     MigrationState *s;
@@ -4425,6 +4434,8 @@ static Property migration_properties[] = {
     DEFINE_PROP_MIG_CAP("x-zero-copy-send",
             MIGRATION_CAPABILITY_ZERO_COPY_SEND),
 #endif
+    DEFINE_PROP_MIG_CAP("main-zero-page",
+            MIGRATION_CAPABILITY_MAIN_ZERO_PAGE),
 
     DEFINE_PROP_END_OF_LIST(),
 };
-- 
2.39.1