[PATCH 4/9] migration: Add direct-io parameter

[Fabiano Rosas]

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 mapped-ram migration that has a
clear window guaranteed to perform aligned writes.

Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 include/qemu/osdep.h           |  2 ++
 migration/migration-hmp-cmds.c | 11 +++++++++++
 migration/options.c            | 30 ++++++++++++++++++++++++++++++
 migration/options.h            |  1 +
 qapi/migration.json            | 18 +++++++++++++++---
 util/osdep.c                   |  9 +++++++++
 6 files changed, 68 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 7e96ae6ffd..8496a2b34e 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -397,6 +397,13 @@ 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);
@@ -690,6 +697,10 @@ 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 239f5ecfb4..ae464aa4f2 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -826,6 +826,22 @@ 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 mapped-ram */
+    if (!s->capabilities[MIGRATION_CAPABILITY_MAPPED_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();
@@ -1061,6 +1077,11 @@ MigrationParameters *qmp_query_migrate_parameters(Error 
**errp)
     params->has_zero_page_detection = true;
     params->zero_page_detection = s->parameters.zero_page_detection;
 
+    if (s->parameters.has_direct_io) {
+        params->has_direct_io = true;
+        params->direct_io = s->parameters.direct_io;
+    }
+
     return params;
 }
 
@@ -1097,6 +1118,7 @@ void migrate_params_init(MigrationParameters *params)
     params->has_vcpu_dirty_limit = true;
     params->has_mode = true;
     params->has_zero_page_detection = true;
+    params->has_direct_io = qemu_has_direct_io();
 }
 
 /*
@@ -1416,6 +1438,10 @@ static void 
migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_zero_page_detection) {
         dest->zero_page_detection = params->zero_page_detection;
     }
+
+    if (params->has_direct_io) {
+        dest->direct_io = params->direct_io;
+    }
 }
 
 static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1570,6 +1596,10 @@ static void migrate_params_apply(MigrateSetParameters 
*params, Error **errp)
     if (params->has_zero_page_detection) {
         s->parameters.zero_page_detection = params->zero_page_detection;
     }
+
+    if (params->has_direct_io) {
+        s->parameters.direct_io = params->direct_io;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
diff --git a/migration/options.h b/migration/options.h
index ab8199e207..aa5509cd2a 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -76,6 +76,7 @@ uint8_t migrate_cpu_throttle_increment(void);
 uint8_t migrate_cpu_throttle_initial(void);
 bool migrate_cpu_throttle_tailslow(void);
 int migrate_decompress_threads(void);
+bool migrate_direct_io(void);
 uint64_t migrate_downtime_limit(void);
 uint8_t migrate_max_cpu_throttle(void);
 uint64_t migrate_max_bandwidth(void);
diff --git a/qapi/migration.json b/qapi/migration.json
index 8c65b90328..1a8a4b114c 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -914,6 +914,9 @@
 #     See description in @ZeroPageDetection.  Default is 'multifd'.
 #     (since 9.0)
 #
+# @direct-io: Open migration files with O_DIRECT when possible. This
+#     requires that the @mapped-ram capability is enabled. (since 9.1)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -948,7 +951,8 @@
            { 'name': 'x-vcpu-dirty-limit-period', 'features': ['unstable'] },
            'vcpu-dirty-limit',
            'mode',
-           'zero-page-detection'] }
+           'zero-page-detection',
+           'direct-io'] }
 
 ##
 # @MigrateSetParameters:
@@ -1122,6 +1126,9 @@
 #     See description in @ZeroPageDetection.  Default is 'multifd'.
 #     (since 9.0)
 #
+# @direct-io: Open migration files with O_DIRECT when possible. This
+#     requires that the @mapped-ram capability is enabled. (since 9.1)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -1176,7 +1183,8 @@
                                             'features': [ 'unstable' ] },
             '*vcpu-dirty-limit': 'uint64',
             '*mode': 'MigMode',
-            '*zero-page-detection': 'ZeroPageDetection'} }
+            '*zero-page-detection': 'ZeroPageDetection',
+            '*direct-io': 'bool' } }
 
 ##
 # @migrate-set-parameters:
@@ -1354,6 +1362,9 @@
 #     See description in @ZeroPageDetection.  Default is 'multifd'.
 #     (since 9.0)
 #
+# @direct-io: Open migration files with O_DIRECT when possible. This
+#     requires that the @mapped-ram capability is enabled. (since 9.1)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -1405,7 +1416,8 @@
                                             'features': [ 'unstable' ] },
             '*vcpu-dirty-limit': 'uint64',
             '*mode': 'MigMode',
-            '*zero-page-detection': 'ZeroPageDetection'} }
+            '*zero-page-detection': 'ZeroPageDetection',
+            '*direct-io': 'bool' } }
 
 ##
 # @query-migrate-parameters:
diff --git a/util/osdep.c b/util/osdep.c
index e996c4744a..d0227a60ab 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -277,6 +277,15 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, 
bool exclusive)
 }
 #endif
 
+bool qemu_has_direct_io(void)
+{
+#ifdef O_DIRECT
+    return true;
+#else
+    return false;
+#endif
+}
+
 static int qemu_open_cloexec(const char *name, int flags, mode_t mode)
 {
     int ret;
-- 
2.35.3