migration: Add direct-io parameter
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>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index f61edcf..191916f 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -612,6 +612,8 @@
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 9f0e802..7d608d2 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -351,6 +351,13 @@
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);
@@ -624,6 +631,10 @@
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 5ab5b6d..645f550 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -702,6 +702,25 @@
return s->parameters.cpu_throttle_tailslow;
}
+bool migrate_direct_io(void)
+{
+ MigrationState *s = migrate_get_current();
+
+ /*
+ * O_DIRECT is only supported with mapped-ram and multifd.
+ *
+ * mapped-ram is needed because filesystems impose restrictions on
+ * O_DIRECT IO alignment (see MAPPED_RAM_FILE_OFFSET_ALIGNMENT).
+ *
+ * multifd is needed to keep the unaligned portion of the stream
+ * isolated to the main migration thread while multifd channels
+ * process the aligned data with O_DIRECT enabled.
+ */
+ return s->parameters.direct_io &&
+ s->capabilities[MIGRATION_CAPABILITY_MAPPED_RAM] &&
+ s->capabilities[MIGRATION_CAPABILITY_MULTIFD];
+}
+
uint64_t migrate_downtime_limit(void)
{
MigrationState *s = migrate_get_current();
@@ -905,6 +924,8 @@
params->mode = s->parameters.mode;
params->has_zero_page_detection = true;
params->zero_page_detection = s->parameters.zero_page_detection;
+ params->has_direct_io = true;
+ params->direct_io = s->parameters.direct_io;
return params;
}
@@ -937,6 +958,7 @@
params->has_vcpu_dirty_limit = true;
params->has_mode = true;
params->has_zero_page_detection = true;
+ params->has_direct_io = true;
}
/*
@@ -1110,6 +1132,11 @@
return false;
}
+ if (params->has_direct_io && params->direct_io && !qemu_has_direct_io()) {
+ error_setg(errp, "No build-time support for direct-io");
+ return false;
+ }
+
return true;
}
@@ -1216,6 +1243,10 @@
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)
@@ -1341,6 +1372,10 @@
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 4b21cc2..a239702 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -69,6 +69,7 @@
uint8_t migrate_cpu_throttle_increment(void);
uint8_t migrate_cpu_throttle_initial(void);
bool migrate_cpu_throttle_tailslow(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 470f746..de6c8b0 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -821,6 +821,10 @@
# See description in @ZeroPageDetection. Default is 'multifd'.
# (since 9.0)
#
+# @direct-io: Open migration files with O_DIRECT when possible. This
+# only has effect if the @mapped-ram capability is enabled.
+# (Since 9.1)
+#
# Features:
#
# @unstable: Members @x-checkpoint-delay and
@@ -845,7 +849,8 @@
{ 'name': 'x-vcpu-dirty-limit-period', 'features': ['unstable'] },
'vcpu-dirty-limit',
'mode',
- 'zero-page-detection'] }
+ 'zero-page-detection',
+ 'direct-io'] }
##
# @MigrateSetParameters:
@@ -991,6 +996,10 @@
# See description in @ZeroPageDetection. Default is 'multifd'.
# (since 9.0)
#
+# @direct-io: Open migration files with O_DIRECT when possible. This
+# only has effect if the @mapped-ram capability is enabled.
+# (Since 9.1)
+#
# Features:
#
# @unstable: Members @x-checkpoint-delay and
@@ -1030,7 +1039,8 @@
'features': [ 'unstable' ] },
'*vcpu-dirty-limit': 'uint64',
'*mode': 'MigMode',
- '*zero-page-detection': 'ZeroPageDetection'} }
+ '*zero-page-detection': 'ZeroPageDetection',
+ '*direct-io': 'bool' } }
##
# @migrate-set-parameters:
@@ -1190,6 +1200,10 @@
# See description in @ZeroPageDetection. Default is 'multifd'.
# (since 9.0)
#
+# @direct-io: Open migration files with O_DIRECT when possible. This
+# only has effect if the @mapped-ram capability is enabled.
+# (Since 9.1)
+#
# Features:
#
# @unstable: Members @x-checkpoint-delay and
@@ -1226,7 +1240,8 @@
'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 5bbfdfa..7703698 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -282,6 +282,15 @@
}
#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;
