[PATCH v4 0/4] migration: do not exit on incoming failure

[PATCH v4 0/4] migration: do not exit on incoming failure

[Vladimir Sementsov-Ogievskiy]

Hi all!

The series brings an option to not immediately exit on incoming
migration failure, giving a possibility to orchestrator to get the error
through QAPI and shutdown QEMU by "quit".

v4:
- add r-b and a-b by Fabiano and Markus
- improve wording in 04 as Markus suggested

v3:
- don't refactor the whole code around setting migration error, it seems
  too much and necessary for the new feature itself
- add constant
- change behavior for HMP command
- split some things to separate patches
- and more, by Peter's suggestions


New behavior can be demonstrated like this:

bash:

(
cat <<EOF
{'execute': 'qmp_capabilities'}
{'execute': 'migrate-set-capabilities', 'arguments': {'capabilities': [{'capability': 'events', 'state': true}]}}
{'execute': 'migrate-incoming', 'arguments': {'uri': 'exec:echo x', 'exit-on-error': false}}
EOF
sleep 1
cat <<EOF
{'execute': 'query-migrate'}
{'execute': 'quit'}
EOF
) | ./build/qemu-system-x86_64 -incoming 'defer' -qmp stdio -nographic -nodefaults

output:

{"QMP": {"version": {"qemu": {"micro": 50, "minor": 0, "major": 9}, "package": "v9.0.0-149-gb6295ad58c"}, "capabilities": ["oob"]}}
{"return": {}}
{"return": {}}
{"timestamp": {"seconds": 1714068847, "microseconds": 263907}, "event": "MIGRATION", "data": {"status": "setup"}}
{"return": {}}
{"timestamp": {"seconds": 1714068847, "microseconds": 266696}, "event": "MIGRATION", "data": {"status": "active"}}
qemu-system-x86_64: Not a migration stream
{"timestamp": {"seconds": 1714068847, "microseconds": 266766}, "event": "MIGRATION", "data": {"status": "failed"}}
{"return": {"status": "failed", "error-desc": "load of migration failed: Invalid argument"}}
{"timestamp": {"seconds": 1714068848, "microseconds": 237187}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
{"return": {}}


Vladimir Sementsov-Ogievskiy (4):
  migration: move trace-point from migrate_fd_error to migrate_set_error
  migration: process_incoming_migration_co(): complete cleanup on
    failure
  migration: process_incoming_migration_co(): rework error reporting
  qapi: introduce exit-on-error parameter for migrate-incoming

 migration/migration-hmp-cmds.c |  2 +-
 migration/migration.c          | 57 ++++++++++++++++++++++++----------
 migration/migration.h          |  3 ++
 migration/trace-events         |  2 +-
 qapi/migration.json            |  7 ++++-
 system/vl.c                    |  3 +-
 6 files changed, 54 insertions(+), 20 deletions(-)

-- 
2.34.1

[PATCH v4 1/4] migration: move trace-point from migrate_fd_error to migrate_set_error

[Vladimir Sementsov-Ogievskiy]

Cover more cases by trace-point.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
---
 migration/migration.c  | 4 +++-
 migration/trace-events | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index b5af6b5105..2dc6a063e9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1421,6 +1421,9 @@ static void migrate_fd_cleanup_bh(void *opaque)
 void migrate_set_error(MigrationState *s, const Error *error)
 {
     QEMU_LOCK_GUARD(&s->error_mutex);
+
+    trace_migrate_error(error_get_pretty(error));
+
     if (!s->error) {
         s->error = error_copy(error);
     }
@@ -1444,7 +1447,6 @@ static void migrate_error_free(MigrationState *s)
 
 static void migrate_fd_error(MigrationState *s, const Error *error)
 {
-    trace_migrate_fd_error(error_get_pretty(error));
     assert(s->to_dst_file == NULL);
     migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                       MIGRATION_STATUS_FAILED);
diff --git a/migration/trace-events b/migration/trace-events
index f0e1cb80c7..d0c44c3853 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -152,7 +152,7 @@ multifd_set_outgoing_channel(void *ioc, const char *ioctype, const char *hostnam
 # migration.c
 migrate_set_state(const char *new_state) "new state %s"
 migrate_fd_cleanup(void) ""
-migrate_fd_error(const char *error_desc) "error=%s"
+migrate_error(const char *error_desc) "error=%s"
 migrate_fd_cancel(void) ""
 migrate_handle_rp_req_pages(const char *rbname, size_t start, size_t len) "in %s at 0x%zx len 0x%zx"
 migrate_pending_exact(uint64_t size, uint64_t pre, uint64_t post) "exact pending size %" PRIu64 " (pre = %" PRIu64 " post=%" PRIu64 ")"
-- 
2.34.1

Re: [PATCH v4 1/4] migration: move trace-point from migrate_fd_error to migrate_set_error

[Peter Xu]

On Mon, Apr 29, 2024 at 10:55:38AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Cover more cases by trace-point.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> Reviewed-by: Fabiano Rosas <farosas@suse.de>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

[PATCH v4 2/4] migration: process_incoming_migration_co(): complete cleanup on failure

[Vladimir Sementsov-Ogievskiy]

Make call to migration_incoming_state_destroy(), instead of doing only
partial of it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
---
 migration/migration.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 2dc6a063e9..0d26db47f7 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -799,10 +799,7 @@ process_incoming_migration_co(void *opaque)
 fail:
     migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_FAILED);
-    qemu_fclose(mis->from_src_file);
-
-    multifd_recv_cleanup();
-    compress_threads_load_cleanup();
+    migration_incoming_state_destroy();
 
     exit(EXIT_FAILURE);
 }
-- 
2.34.1

[PATCH v4 3/4] migration: process_incoming_migration_co(): rework error reporting

[Vladimir Sementsov-Ogievskiy]

Unify error reporting in the function. This simplifies the following
commit, which will not-exit-on-error behavior variant to the function.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
---
 migration/migration.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 0d26db47f7..0b15f7ccf4 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -735,14 +735,16 @@ static void process_incoming_migration_bh(void *opaque)
 static void coroutine_fn
 process_incoming_migration_co(void *opaque)
 {
+    MigrationState *s = migrate_get_current();
     MigrationIncomingState *mis = migration_incoming_get_current();
     PostcopyState ps;
     int ret;
+    Error *local_err = NULL;
 
     assert(mis->from_src_file);
 
     if (compress_threads_load_setup(mis->from_src_file)) {
-        error_report("Failed to setup decompress threads");
+        error_setg(&local_err, "Failed to setup decompress threads");
         goto fail;
     }
 
@@ -779,18 +781,12 @@ process_incoming_migration_co(void *opaque)
     }
 
     if (ret < 0) {
-        MigrationState *s = migrate_get_current();
-
-        if (migrate_has_error(s)) {
-            WITH_QEMU_LOCK_GUARD(&s->error_mutex) {
-                error_report_err(s->error);
-            }
-        }
-        error_report("load of migration failed: %s", strerror(-ret));
+        error_setg(&local_err, "load of migration failed: %s", strerror(-ret));
         goto fail;
     }
 
     if (colo_incoming_co() < 0) {
+        error_setg(&local_err, "colo incoming failed");
         goto fail;
     }
 
@@ -801,6 +797,12 @@ fail:
                       MIGRATION_STATUS_FAILED);
     migration_incoming_state_destroy();
 
+    if (migrate_has_error(s)) {
+        WITH_QEMU_LOCK_GUARD(&s->error_mutex) {
+            error_report_err(s->error);
+        }
+    }
+    error_report_err(local_err);
     exit(EXIT_FAILURE);
 }
 
-- 
2.34.1

[PATCH v4 4/4] qapi: introduce exit-on-error parameter for migrate-incoming

[Vladimir Sementsov-Ogievskiy]

Now we do set MIGRATION_FAILED state, but don't give a chance to
orchestrator to query migration state and get the error.

Let's provide a possibility for QMP-based orchestrators to get an error
like with outgoing migration.

For hmp_migrate_incoming(), let's enable the new behavior: HMP is not
and ABI, it's mostly intended to use by developer and it makes sense
not to stop the process.

For x-exit-preconfig, let's keep the old behavior:
 - it's called from init(), so here we want to keep current behavior by
   default
 - it does exit on error by itself as well
So, if we want to change the behavior of x-exit-preconfig, it should be
another patch.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Acked-by: Markus Armbruster <armbru@redhat.com>
---
 migration/migration-hmp-cmds.c |  2 +-
 migration/migration.c          | 36 ++++++++++++++++++++++++++++------
 migration/migration.h          |  3 +++
 qapi/migration.json            |  7 ++++++-
 system/vl.c                    |  3 ++-
 5 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
index 7e96ae6ffd..23181bbee1 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -466,7 +466,7 @@ void hmp_migrate_incoming(Monitor *mon, const QDict *qdict)
     }
     QAPI_LIST_PREPEND(caps, g_steal_pointer(&channel));
 
-    qmp_migrate_incoming(NULL, true, caps, &err);
+    qmp_migrate_incoming(NULL, true, caps, true, false, &err);
     qapi_free_MigrationChannelList(caps);
 
 end:
diff --git a/migration/migration.c b/migration/migration.c
index 0b15f7ccf4..5cfe420a76 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -72,6 +72,8 @@
 #define NOTIFIER_ELEM_INIT(array, elem)    \
     [elem] = NOTIFIER_WITH_RETURN_LIST_INITIALIZER((array)[elem])
 
+#define INMIGRATE_DEFAULT_EXIT_ON_ERROR true
+
 static NotifierWithReturnList migration_state_notifiers[] = {
     NOTIFIER_ELEM_INIT(migration_state_notifiers, MIG_MODE_NORMAL),
     NOTIFIER_ELEM_INIT(migration_state_notifiers, MIG_MODE_CPR_REBOOT),
@@ -234,6 +236,8 @@ void migration_object_init(void)
     qemu_cond_init(&current_incoming->page_request_cond);
     current_incoming->page_requested = g_tree_new(page_request_addr_cmp);
 
+    current_incoming->exit_on_error = INMIGRATE_DEFAULT_EXIT_ON_ERROR;
+
     migration_object_check(current_migration, &error_fatal);
 
     blk_mig_init();
@@ -797,13 +801,18 @@ fail:
                       MIGRATION_STATUS_FAILED);
     migration_incoming_state_destroy();
 
-    if (migrate_has_error(s)) {
-        WITH_QEMU_LOCK_GUARD(&s->error_mutex) {
-            error_report_err(s->error);
+    if (mis->exit_on_error) {
+        if (migrate_has_error(s)) {
+            WITH_QEMU_LOCK_GUARD(&s->error_mutex) {
+                error_report_err(s->error);
+            }
         }
+        error_report_err(local_err);
+        exit(EXIT_FAILURE);
+    } else {
+        migrate_set_error(s, local_err);
+        error_free(local_err);
     }
-    error_report_err(local_err);
-    exit(EXIT_FAILURE);
 }
 
 /**
@@ -1312,6 +1321,15 @@ static void fill_destination_migration_info(MigrationInfo *info)
         break;
     }
     info->status = mis->state;
+
+    if (!info->error_desc) {
+        MigrationState *s = migrate_get_current();
+        QEMU_LOCK_GUARD(&s->error_mutex);
+
+        if (s->error) {
+            info->error_desc = g_strdup(error_get_pretty(s->error));
+        }
+    }
 }
 
 MigrationInfo *qmp_query_migrate(Error **errp)
@@ -1795,10 +1813,13 @@ void migrate_del_blocker(Error **reasonp)
 }
 
 void qmp_migrate_incoming(const char *uri, bool has_channels,
-                          MigrationChannelList *channels, Error **errp)
+                          MigrationChannelList *channels,
+                          bool has_exit_on_error, bool exit_on_error,
+                          Error **errp)
 {
     Error *local_err = NULL;
     static bool once = true;
+    MigrationIncomingState *mis = migration_incoming_get_current();
 
     if (!once) {
         error_setg(errp, "The incoming migration has already been started");
@@ -1813,6 +1834,9 @@ void qmp_migrate_incoming(const char *uri, bool has_channels,
         return;
     }
 
+    mis->exit_on_error =
+        has_exit_on_error ? exit_on_error : INMIGRATE_DEFAULT_EXIT_ON_ERROR;
+
     qemu_start_incoming_migration(uri, has_channels, channels, &local_err);
 
     if (local_err) {
diff --git a/migration/migration.h b/migration/migration.h
index 8045e39c26..95995a818e 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -227,6 +227,9 @@ struct MigrationIncomingState {
      * is needed as this field is updated serially.
      */
     unsigned int switchover_ack_pending_num;
+
+    /* Do exit on incoming migration failure */
+    bool exit_on_error;
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);
diff --git a/qapi/migration.json b/qapi/migration.json
index 8c65b90328..9feed413b5 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1837,6 +1837,10 @@
 # @channels: list of migration stream channels with each stream in the
 #     list connected to a destination interface endpoint.
 #
+# @exit-on-error: Exit on incoming migration failure.  Default true.
+#     When set to false, the failure triggers a MIGRATION event, and
+#     error details could be retrieved with query-migrate.  (since 9.1)
+#
 # Since: 2.3
 #
 # Notes:
@@ -1889,7 +1893,8 @@
 ##
 { 'command': 'migrate-incoming',
              'data': {'*uri': 'str',
-                      '*channels': [ 'MigrationChannel' ] } }
+                      '*channels': [ 'MigrationChannel' ],
+                      '*exit-on-error': 'bool' } }
 
 ##
 # @xen-save-devices-state:
diff --git a/system/vl.c b/system/vl.c
index 7756eac81e..79cd498395 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -2723,7 +2723,8 @@ void qmp_x_exit_preconfig(Error **errp)
     if (incoming) {
         Error *local_err = NULL;
         if (strcmp(incoming, "defer") != 0) {
-            qmp_migrate_incoming(incoming, false, NULL, &local_err);
+            qmp_migrate_incoming(incoming, false, NULL, true, true,
+                                 &local_err);
             if (local_err) {
                 error_reportf_err(local_err, "-incoming %s: ", incoming);
                 exit(1);
-- 
2.34.1