[PATCH v4 27/34] migration: Add direct-io parameter

[Fabiano Rosas <farosas@suse.de>]

Add the direct-io migration parameter that tells the migration code to
use O_DIRECT when opening the migration stream file whenever possible.

This is currently only used with the fixed-ram migration that has a
clear window guaranteed to perform aligned writes.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 include/qemu/osdep.h           |  2 ++
 migration/migration-hmp-cmds.c | 11 +++++++++++
 migration/options.c            | 30 ++++++++++++++++++++++++++++++
 qapi/migration.json            | 18 +++++++++++++++---
 4 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index c7053cdc2b..645c14a65d 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -612,6 +612,8 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive);
 bool qemu_has_ofd_lock(void);
 #endif
 
+bool qemu_has_direct_io(void);
+
 #if defined(__HAIKU__) && defined(__i386__)
 #define FMT_pid "%ld"
 #elif defined(WIN64)
diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
index 99b49df5dd..77313346c2 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -392,6 +392,13 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "%s: %s\n",
             MigrationParameter_str(MIGRATION_PARAMETER_MODE),
             qapi_enum_lookup(&MigMode_lookup, params->mode));
+
+        if (params->has_direct_io) {
+            monitor_printf(mon, "%s: %s\n",
+                           MigrationParameter_str(
+                               MIGRATION_PARAMETER_DIRECT_IO),
+                           params->direct_io ? "on" : "off");
+        }
     }
 
     qapi_free_MigrationParameters(params);
@@ -681,6 +688,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
         p->has_mode = true;
         visit_type_MigMode(v, param, &p->mode, &err);
         break;
+    case MIGRATION_PARAMETER_DIRECT_IO:
+        p->has_direct_io = true;
+        visit_type_bool(v, param, &p->direct_io, &err);
+        break;
     default:
         assert(0);
     }
diff --git a/migration/options.c b/migration/options.c
index bfcd2d7132..b347dbc670 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -823,6 +823,22 @@ int migrate_decompress_threads(void)
     return s->parameters.decompress_threads;
 }
 
+bool migrate_direct_io(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    /* For now O_DIRECT is only supported with fixed-ram */
+    if (!s->capabilities[MIGRATION_CAPABILITY_FIXED_RAM]) {
+        return false;
+    }
+
+    if (s->parameters.has_direct_io) {
+        return s->parameters.direct_io;
+    }
+
+    return false;
+}
+
 uint64_t migrate_downtime_limit(void)
 {
     MigrationState *s = migrate_get_current();
@@ -1042,6 +1058,11 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->has_mode = true;
     params->mode = s->parameters.mode;
 
+    if (s->parameters.has_direct_io) {
+        params->has_direct_io = true;
+        params->direct_io = s->parameters.direct_io;
+    }
+
     return params;
 }
 
@@ -1077,6 +1098,7 @@ void migrate_params_init(MigrationParameters *params)
     params->has_x_vcpu_dirty_limit_period = true;
     params->has_vcpu_dirty_limit = true;
     params->has_mode = true;
+    params->has_direct_io = qemu_has_direct_io();
 }
 
 /*
@@ -1386,6 +1408,10 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_mode) {
         dest->mode = params->mode;
     }
+
+    if (params->has_direct_io) {
+        dest->direct_io = params->direct_io;
+    }
 }
 
 static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1530,6 +1556,10 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_mode) {
         s->parameters.mode = params->mode;
     }
+
+    if (params->has_direct_io) {
+        s->parameters.direct_io = params->direct_io;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
diff --git a/qapi/migration.json b/qapi/migration.json
index 3fce5fe53e..41241a2178 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -878,6 +878,9 @@
 # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
 #        (Since 8.2)
 #
+# @direct-io: Open migration files with O_DIRECT when possible. This
+#     requires that the 'fixed-ram' capability is enabled. (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -911,7 +914,8 @@
            'block-bitmap-mapping',
            { 'name': 'x-vcpu-dirty-limit-period', 'features': ['unstable'] },
            'vcpu-dirty-limit',
-           'mode'] }
+           'mode',
+           'direct-io'] }
 
 ##
 # @MigrateSetParameters:
@@ -1070,6 +1074,9 @@
 # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
 #        (Since 8.2)
 #
+# @direct-io: Open migration files with O_DIRECT when possible. This
+#     requires that the 'fixed-ram' capability is enabled. (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -1123,7 +1130,8 @@
             '*x-vcpu-dirty-limit-period': { 'type': 'uint64',
                                             'features': [ 'unstable' ] },
             '*vcpu-dirty-limit': 'uint64',
-            '*mode': 'MigMode'} }
+            '*mode': 'MigMode',
+            '*direct-io': 'bool' } }
 
 ##
 # @migrate-set-parameters:
@@ -1298,6 +1306,9 @@
 # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
 #        (Since 8.2)
 #
+# @direct-io: Open migration files with O_DIRECT when possible. This
+#     requires that the 'fixed-ram' capability is enabled. (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -1348,7 +1359,8 @@
             '*x-vcpu-dirty-limit-period': { 'type': 'uint64',
                                             'features': [ 'unstable' ] },
             '*vcpu-dirty-limit': 'uint64',
-            '*mode': 'MigMode'} }
+            '*mode': 'MigMode',
+            '*direct-io': 'bool' } }
 
 ##
 # @query-migrate-parameters:
-- 
2.35.3