[Qemu-devel] [PATCH 03/12] migration: create new section to store global state

[Juan Quintela]

This includes a new section that for now just stores the current qemu state.

Right now, there are only one way to control what is the state of the
target after migration.

- If you run the target qemu with -S, it would start stopped.
- If you run the target qemu without -S, it would run just after migration 
finishes.

The problem here is what happens if we start the target without -S and
there happens one error during migration that puts current state as
-EIO.  Migration would ends (notice that the error happend doing block
IO, network IO, i.e. nothing related with migration), and when
migration finish, we would just "continue" running on destination,
probably hanging the guest/corruption data, whatever.

Signed-off-by: Juan Quintela <address@hidden>
---
 include/migration/migration.h |   1 +
 migration/migration.c         | 105 +++++++++++++++++++++++++++++++++++++++---
 trace-events                  |   3 ++
 vl.c                          |   1 +
 4 files changed, 103 insertions(+), 7 deletions(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 9387c8c..1280193 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -197,4 +197,5 @@ size_t ram_control_save_page(QEMUFile *f, ram_addr_t 
block_offset,

 void ram_mig_init(void);
 void savevm_skip_section_footers(void);
+void register_global_state(void);
 #endif
diff --git a/migration/migration.c b/migration/migration.c
index c6ac08a..b4b6d69 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -26,6 +26,7 @@
 #include "qemu/thread.h"
 #include "qmp-commands.h"
 #include "trace.h"
+#include "qapi/util.h"

 #define MAX_THROTTLE  (32 << 20)      /* Migration speed throttling */

@@ -97,6 +98,83 @@ void migration_incoming_state_destroy(void)
     mis_current = NULL;
 }

+
+typedef struct {
+    uint32_t size;
+    uint8_t runstate[100];
+} GlobalState;
+
+static GlobalState global_state;
+
+static int global_state_store(void)
+{
+    if (!runstate_store((char *)global_state.runstate,
+                        sizeof(global_state.runstate))) {
+        trace_migrate_state_too_big();
+        return -EINVAL;
+    }
+    return 0;
+}
+
+static char *global_state_get_runstate(void)
+{
+    return (char *)global_state.runstate;
+}
+
+static int global_state_post_load(void *opaque, int version_id)
+{
+    GlobalState *s = opaque;
+    int ret = 0;
+    char *runstate = (char *)s->runstate;
+
+    trace_migrate_global_state_post_load(runstate);
+
+    if (strcmp(runstate, "running") != 0) {
+        Error *local_err = NULL;
+        int r = qapi_enum_parse(RunState_lookup, runstate, RUN_STATE_MAX,
+                                -1, &local_err);
+
+        if (r == -1) {
+            if (local_err) {
+                error_report_err(local_err);
+            }
+            return -EINVAL;
+        }
+        ret = vm_stop_force_state(r);
+    }
+
+   return ret;
+}
+
+static void global_state_pre_save(void *opaque)
+{
+    GlobalState *s = opaque;
+
+    trace_migrate_global_state_pre_save((char *)s->runstate);
+    s->size = strlen((char *)s->runstate) + 1;
+    printf("saved state: %s\n", s->runstate);
+}
+
+static const VMStateDescription vmstate_globalstate = {
+    .name = "globalstate",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .post_load = global_state_post_load,
+    .pre_save = global_state_pre_save,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(size, GlobalState),
+        VMSTATE_BUFFER(runstate, GlobalState),
+        VMSTATE_END_OF_LIST()
+    },
+};
+
+void register_global_state(void)
+{
+    /* We would use it independently that we receive it */
+    strcpy((char *)&global_state.runstate, "");
+    vmstate_register(NULL, 0, &vmstate_globalstate, &global_state);
+}
+
 /*
  * Called on -incoming with a defer: uri.
  * The migration can be started later after any parameters have been
@@ -164,10 +242,20 @@ static void process_incoming_migration_co(void *opaque)
         exit(EXIT_FAILURE);
     }

-    if (autostart) {
+    /* runstate == "" means that we haven't received it through the
+     * wire, so we obey autostart.  runstate == runing means that we
+     * need to run it, we need to make sure that we do it after
+     * everything else has finished.  Every other state change is done
+     * at the post_load function */
+
+    if (strcmp(global_state_get_runstate(), "running") == 0) {
         vm_start();
-    } else {
-        runstate_set(RUN_STATE_PAUSED);
+    } else if (strcmp(global_state_get_runstate(), "") == 0) {
+        if (autostart) {
+            vm_start();
+        } else {
+            runstate_set(RUN_STATE_PAUSED);
+        }
     }
     migrate_decompress_threads_join();
 }
@@ -793,10 +881,13 @@ static void *migration_thread(void *opaque)
                 qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
                 old_vm_running = runstate_is_running();

-                ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
-                if (ret >= 0) {
-                    qemu_file_set_rate_limit(s->file, INT64_MAX);
-                    qemu_savevm_state_complete(s->file);
+                ret = global_state_store();
+                if (!ret) {
+                    ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
+                    if (ret >= 0) {
+                        qemu_file_set_rate_limit(s->file, INT64_MAX);
+                        qemu_savevm_state_complete(s->file);
+                    }
                 }
                 qemu_mutex_unlock_iothread();

diff --git a/trace-events b/trace-events
index 52b7efa..5d5cae2 100644
--- a/trace-events
+++ b/trace-events
@@ -1403,6 +1403,9 @@ migrate_fd_error(void) ""
 migrate_fd_cancel(void) ""
 migrate_pending(uint64_t size, uint64_t max) "pending size %" PRIu64 " max %" 
PRIu64
 migrate_transferred(uint64_t tranferred, uint64_t time_spent, double 
bandwidth, uint64_t size) "transferred %" PRIu64 " time_spent %" PRIu64 " 
bandwidth %g max_size %" PRId64
+migrate_state_too_big(void) ""
+migrate_global_state_post_load(const char *state) "loaded state: %s"
+migrate_global_state_pre_save(const char *state) "saved state: %s"

 # migration/rdma.c
 qemu_dma_accept_incoming_migration(void) ""
diff --git a/vl.c b/vl.c
index d4d9ca8..ce39f60 100644
--- a/vl.c
+++ b/vl.c
@@ -4624,6 +4624,7 @@ int main(int argc, char **argv, char **envp)
         return 0;
     }

+    register_global_state();
     if (incoming) {
         Error *local_err = NULL;
         qemu_start_incoming_migration(incoming, &local_err);
-- 
2.4.3