Re: [Qemu-devel] [PULL 15/28] migration: create new section to store global state

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Christian Borntraeger (borntraeger@de.ibm.com) wrote:
> Am 07.07.2015 um 15:08 schrieb 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 <quintela@redhat.com>
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> This is bisected to cause a regression on s390.
> 
> A guest restarts (booting) after managedsave/start instead of continuing.
> 
> Do you have any idea what might be wrong?

I'd add some debug to the pre_save and post_load to see what state value is
being saved/restored.

Also, does that regression happen when doing the save/restore using the same/latest
git, or is it a load from an older version?

Dave

> 
> > ---
> >  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 afba233..86df6cc 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..5e436f7 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))) {
> > +        error_report("runstate name too big: %s", 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;
> > +}
> > +
> > +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 a38dd2e..c0111d0 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_rdma_accept_incoming_migration(void) ""
> > diff --git a/vl.c b/vl.c
> > index 19a8737..cfa6133 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);
> > 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK