Re: [Qemu-devel] [PATCH 08/29] migration (outgoing): add error propagation for all protocols

[Markus Armbruster]

Paolo Bonzini <address@hidden> writes:

> Error propagation is already there for socket backends.  Add it to other
> protocols, simplifying code that tests for errors that will never happen.
> With all protocols understanding Error, the code can be simplified
> further by removing the return value.
>
> Unfortunately, the quality of error messages varies depending
> on where the error is detected, because no Error is passed to the
> NonBlockingConnectHandler.  Thus, the exact error message still cannot
> be sent to the user if the OS reports it asynchronously via SO_ERROR.
> If NonBlockingConnectHandler received an Error**, we could for
> example report the error class and/or message via a new field of the
> query-migration command even if it is reported asynchronously.
>
> Before:
>
>     (qemu) migrate fd:ffff
>     migrate: An undefined error has occurred
>     (qemu) info migrate
>     (qemu)
>
> After:
>
>     (qemu) migrate fd:ffff
>     migrate: File descriptor named 'ffff' has not been found
>     (qemu) info migrate
>     capabilities: xbzrle: off
>     Migration status: failed
>     total time: 0 milliseconds
[...]
> diff --git a/migration-fd.c b/migration-fd.c
> index 7335167..a7c800a 100644
> --- a/migration-fd.c
> +++ b/migration-fd.c
> @@ -73,30 +73,19 @@ static int fd_close(MigrationState *s)
>      return 0;
>  }
>  
> -int fd_start_outgoing_migration(MigrationState *s, const char *fdname)
> +void fd_start_outgoing_migration(MigrationState *s, const char *fdname, 
> Error **errp)
>  {
> -    s->fd = monitor_get_fd(cur_mon, fdname, NULL);
> +    s->fd = monitor_get_fd(cur_mon, fdname, errp);
>      if (s->fd == -1) {
> -        DPRINTF("fd_migration: invalid file descriptor identifier\n");
> -        goto err_after_get_fd;
> -    }
> -
> -    if (fcntl(s->fd, F_SETFL, O_NONBLOCK) == -1) {
> -        DPRINTF("Unable to set nonblocking mode on file descriptor\n");
> -        goto err_after_open;
> +        return;
>      }
>  
> +    fcntl(s->fd, F_SETFL, O_NONBLOCK);

Sure this can't fail?

>      s->get_error = fd_errno;
>      s->write = fd_write;
>      s->close = fd_close;
>  
>      migrate_fd_connect(s);
> -    return 0;
> -
> -err_after_open:
> -    close(s->fd);
> -err_after_get_fd:
> -    return -1;
>  }
>  
>  static void fd_accept_incoming_migration(void *opaque)
[...]