Re: [Qemu-devel] [RFC v2 16/33] migration: rebuild channel on source

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

* Peter Xu (peterx@redhat.com) wrote:
> This patch detects the "resume" flag of migration command, rebuild the
> channels only if the flag is set.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/migration.c | 92 ++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 69 insertions(+), 23 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 15b8eb1..deb947b 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1233,49 +1233,75 @@ bool migration_is_blocked(Error **errp)
>      return false;
>  }
>  
> -void qmp_migrate(const char *uri, bool has_blk, bool blk,
> -                 bool has_inc, bool inc, bool has_detach, bool detach,
> -                 bool has_resume, bool resume, Error **errp)
> +/* Returns true if continue to migrate, or false if error detected */
> +static bool migrate_prepare(MigrationState *s, bool blk, bool blk_inc,
> +                            bool resume, Error **errp)
>  {
>      Error *local_err = NULL;
> -    MigrationState *s = migrate_get_current();
> -    const char *p;
> +
> +    if (resume) {
> +        if (s->state != MIGRATION_STATUS_POSTCOPY_PAUSED) {
> +            error_setg(errp, "Cannot resume if there is no "
> +                       "paused migration");
> +            return false;
> +        }
> +        /* This is a resume, skip init status */
> +        return true;
> +    }
>  
>      if (migration_is_setup_or_active(s->state) ||
>          s->state == MIGRATION_STATUS_CANCELLING ||
>          s->state == MIGRATION_STATUS_COLO) {
>          error_setg(errp, QERR_MIGRATION_ACTIVE);
> -        return;
> +        return false;
>      }
> +
>      if (runstate_check(RUN_STATE_INMIGRATE)) {
>          error_setg(errp, "Guest is waiting for an incoming migration");
> -        return;
> +        return false;
>      }
>  
>      if (migration_is_blocked(errp)) {
> -        return;
> +        return false;
>      }
>  
> -    if ((has_blk && blk) || (has_inc && inc)) {
> +    if (blk || blk_inc) {
>          if (migrate_use_block() || migrate_use_block_incremental()) {
>              error_setg(errp, "Command options are incompatible with "
>                         "current migration capabilities");
> -            return;
> +            return false;
>          }
>          migrate_set_block_enabled(true, &local_err);
>          if (local_err) {
>              error_propagate(errp, local_err);
> -            return;
> +            return false;
>          }
>          s->must_remove_block_options = true;
>      }
>  
> -    if (has_inc && inc) {
> +    if (blk_inc) {
>          migrate_set_block_incremental(s, true);
>      }
>  
>      migrate_init(s);
>  
> +    return true;
> +}
> +
> +void qmp_migrate(const char *uri, bool has_blk, bool blk,
> +                 bool has_inc, bool inc, bool has_detach, bool detach,
> +                 bool has_resume, bool resume, Error **errp)
> +{
> +    Error *local_err = NULL;
> +    MigrationState *s = migrate_get_current();
> +    const char *p;
> +
> +    if (!migrate_prepare(s, has_blk && blk, has_inc && inc,
> +                         has_resume && resume, errp)) {
> +        /* Error detected, put into errp */
> +        return;
> +    }
> +
>      if (strstart(uri, "tcp:", &p)) {
>          tcp_start_outgoing_migration(s, p, &local_err);
>  #ifdef CONFIG_RDMA
> @@ -1697,7 +1723,8 @@ out:
>      return NULL;
>  }
>  
> -static int open_return_path_on_source(MigrationState *ms)
> +static int open_return_path_on_source(MigrationState *ms,
> +                                      bool create_thread)
>  {
>  
>      ms->rp_state.from_dst_file = qemu_file_get_return_path(ms->to_dst_file);
> @@ -1706,6 +1733,12 @@ static int open_return_path_on_source(MigrationState *ms)
>      }
>  
>      trace_open_return_path_on_source();
> +
> +    if (!create_thread) {
> +        /* We're done */
> +        return 0;
> +    }
> +
>      qemu_thread_create(&ms->rp_state.rp_thread, "return path",
>                         source_return_path_thread, ms, QEMU_THREAD_JOINABLE);
>  
> @@ -2263,15 +2296,24 @@ static void *migration_thread(void *opaque)
>  
>  void migrate_fd_connect(MigrationState *s)
>  {
> -    s->expected_downtime = s->parameters.downtime_limit;
> -    s->cleanup_bh = qemu_bh_new(migrate_fd_cleanup, s);
> +    int64_t rate_limit;
> +    bool resume = s->state == MIGRATION_STATUS_POSTCOPY_PAUSED;
>  
> -    qemu_file_set_blocking(s->to_dst_file, true);
> -    qemu_file_set_rate_limit(s->to_dst_file,
> -                             s->parameters.max_bandwidth / XFER_LIMIT_RATIO);
> +    if (resume) {
> +        /* This is a resumed migration */
> +        rate_limit = INT64_MAX;
> +    } else {
> +        /* This is a fresh new migration */
> +        rate_limit = s->parameters.max_bandwidth / XFER_LIMIT_RATIO;
> +        s->expected_downtime = s->parameters.downtime_limit;
> +        s->cleanup_bh = qemu_bh_new(migrate_fd_cleanup, s);
>  
> -    /* Notify before starting migration thread */
> -    notifier_list_notify(&migration_state_notifiers, s);
> +        /* Notify before starting migration thread */
> +        notifier_list_notify(&migration_state_notifiers, s);
> +    }
> +
> +    qemu_file_set_rate_limit(s->to_dst_file, rate_limit);
> +    qemu_file_set_blocking(s->to_dst_file, true);
>  
>      /*
>       * Open the return path. For postcopy, it is used exclusively. For
> @@ -2279,15 +2321,19 @@ void migrate_fd_connect(MigrationState *s)
>       * QEMU uses the return path.
>       */
>      if (migrate_postcopy_ram() || migrate_use_return_path()) {
> -        if (open_return_path_on_source(s)) {
> +        if (open_return_path_on_source(s, !resume)) {
>              error_report("Unable to open return-path for postcopy");
> -            migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
> -                              MIGRATION_STATUS_FAILED);
> +            migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
>              migrate_fd_cleanup(s);
>              return;
>          }
>      }
>  
> +    if (resume) {
> +        /* TODO: do the resume logic */
> +        return;
> +    }
> +
>      qemu_thread_create(&s->thread, "live_migration", migration_thread, s,
>                         QEMU_THREAD_JOINABLE);
>      s->migration_thread_running = true;
> -- 
> 2.7.4
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK