Re: [Qemu-devel] [PATCH 03/11] migration: create new section to store global state

[Juan Quintela]

"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Juan Quintela (address@hidden) wrote:
>> 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         | 93 
>> +++++++++++++++++++++++++++++++++++++++++--
>>  vl.c                          |  1 +
>>  3 files changed, 92 insertions(+), 3 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 b04b457..01bb90d 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -25,6 +25,7 @@
>>  #include "qemu/thread.h"
>>  #include "qmp-commands.h"
>>  #include "trace.h"
>> +#include "qapi/util.h"
>> 
>>  #define MAX_THROTTLE  (32 << 20)      /* Migration speed throttling */
>> 
>> @@ -96,6 +97,81 @@ void migration_incoming_state_destroy(void)
>>      mis_current = NULL;
>>  }
>> 
>> +
>> +typedef struct {
>> +    int32_t size;
>
> Still think that size should be unsigned.

changed


>
>> +    uint8_t runstate[100];
>> +} GlobalState;
>> +
>> +static GlobalState global_state;
>> +
>> +static void global_state_store(void)
>> +{
>> +    if (!runstate_store((char *)global_state.runstate,
>> +                        sizeof(global_state.runstate))) {
>> +        printf("Runstate is too big\n");
>> +        exit(-1);
>
> Hmmmm:
>   1) Shouldn't that be an error report? or an assert?
>   2) Exit should use EXIT_FAILURE (which is +ve as well)
>   3) But you shouldn't kill the guest on an outwards migration
>      - just fail the migration.
>   4) (And anyway this all seems overkill for sending a 
>       status string).

moved to a trace & and return -EINVAL.  Adjusted only caller to handle
the error.

>
>> +    }
>> +}
>> +
>> +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;
>> +
>> +    printf("loaded state: %s\n", runstate);
>
> trace_.....

Done

>
>> +
>> +    if (strcmp(runstate, "running") != 0) {
>> +        Error *local_err = NULL;
>> +        int r = qapi_enum_parse(RunState_lookup, runstate, RUN_STATE_MAX,
>> +                                -1, &local_err);
>
> Is there a reason not to do the qapi_enum_parse first, and then
> compare it's output to RUN_STATE_RUNNING?

Avoid running the enum_parse at all if we are not at running state, I
don't really care one way or another.

>
>> +
>> +        if (r == -1) {
>> +            if (local_err) {
>> +                error_report_err(local_err);
>> +            }
>> +            return -1;
>
> I'm not sure, but shouldn't that be -EINVAL ?
> (Not that vmstate is consistent about it)

Changed.


>> +        }
>> +        ret = vm_stop_force_state(r);
>
> Kind of going back to adding the state transitions;
> don't you need to allow INMIGRATE to * - because it could
> be pretty much anything? (Shutdown? Suspended?)

good question. Doing the change in the other patch.


>> +    }
>> +
>> +   return ret;
>> +}
>> +
>> +static void global_state_pre_save(void *opaque)
>> +{
>> +    GlobalState *s = opaque;
>> +
>> +    s->size = strlen((char *)s->runstate) + 1;
>> +    printf("saved state: %s\n", s->runstate);
>
> trace_

Done.

>> +}
>> +
>> +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_INT32(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
>> @@ -163,10 +239,20 @@ 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();
>>  }
>> @@ -791,6 +877,7 @@ static void *migration_thread(void *opaque)
>>                  qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
>>                  old_vm_running = runstate_is_running();
>> 
>> +                global_state_store();
>>                  ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
>>                  if (ret >= 0) {
>>                      qemu_file_set_rate_limit(s->file, INT64_MAX);
>> diff --git a/vl.c b/vl.c
>> index 555fd88..95acdb1 100644
>> --- a/vl.c
>> +++ b/vl.c
>> @@ -4473,6 +4473,7 @@ 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
>> 
>> 
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK