Re: [PATCH 10/16] migration: Handle migration_incoming_setup() errors consistently

[Dr. David Alan Gilbert]

* Markus Armbruster (armbru@redhat.com) wrote:
> Commit b673eab4e2 "multifd: Make multifd_load_setup() get an Error
> parameter" changed migration_incoming_setup() to take an Error **
> argument, and adjusted the callers accordingly.  It neglected to
> change adjust multifd_load_setup(): it still exit()s on error.  Clean
> that up.
> 
> The error now gets propagated up two call chains: via
> migration_fd_process_incoming() to rdma_accept_incoming_migration(),
> and via migration_ioc_process_incoming() to
> migration_channel_process_incoming().  Both chain ends report the
> error with error_report_err(), but otherwise ignore it.  Behavioral
> change: we no longer exit() on this error.
> 
> This is consistent with how we handle other errors here, e.g. from
> multifd_recv_new_channel() via migration_ioc_process_incoming() to
> migration_channel_process_incoming().  Wether it's consistently right
> or consistently wrong I can't tell.
> 
> Also clean up the return value from the unusual 0 on success, 1 on
> error to the more common true on success, false on error.
> 
> Cc: Juan Quintela <quintela@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  migration/migration.c | 27 +++++++++------------------
>  1 file changed, 9 insertions(+), 18 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 231dc24414..c1c0a48647 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -609,30 +609,25 @@ fail:
>  }
>  
>  /**
> - * @migration_incoming_setup: Setup incoming migration
> - *
> - * Returns 0 for no error or 1 for error
> - *
> + * migration_incoming_setup: Setup incoming migration
>   * @f: file for main migration channel
>   * @errp: where to put errors
> + *
> + * Returns: %true on success, %false on error.
>   */
> -static int migration_incoming_setup(QEMUFile *f, Error **errp)
> +static bool migration_incoming_setup(QEMUFile *f, Error **errp)
>  {
>      MigrationIncomingState *mis = migration_incoming_get_current();
> -    Error *local_err = NULL;
>  
> -    if (multifd_load_setup(&local_err) != 0) {
> -        /* We haven't been able to create multifd threads
> -           nothing better to do */
> -        error_report_err(local_err);
> -        exit(EXIT_FAILURE);
> +    if (multifd_load_setup(errp) != 0) {
> +        return false;
>      }

What I don't know is how well that will survive; for example in
multifd_load_setup it creates multiple threads and calls the recv_setup
member on each thread; now if one of those fails what happens - if we
don't exit, is it cleaned up enough so you can try another
migrate_incoming or is it just going to fall over?

Dave

>  
>      if (!mis->from_src_file) {
>          mis->from_src_file = f;
>      }
>      qemu_file_set_blocking(f, false);
> -    return 0;
> +    return true;
>  }
>  
>  void migration_incoming_process(void)
> @@ -675,14 +670,11 @@ static bool postcopy_try_recover(QEMUFile *f)
>  
>  void migration_fd_process_incoming(QEMUFile *f, Error **errp)
>  {
> -    Error *local_err = NULL;
> -
>      if (postcopy_try_recover(f)) {
>          return;
>      }
>  
> -    if (migration_incoming_setup(f, &local_err)) {
> -        error_propagate(errp, local_err);
> +    if (!migration_incoming_setup(f, errp)) {
>          return;
>      }
>      migration_incoming_process();
> @@ -703,8 +695,7 @@ void migration_ioc_process_incoming(QIOChannel *ioc, 
> Error **errp)
>              return;
>          }
>  
> -        if (migration_incoming_setup(f, &local_err)) {
> -            error_propagate(errp, local_err);
> +        if (!migration_incoming_setup(f, errp)) {
>              return;
>          }
>  
> -- 
> 2.31.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK