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Re: [libvirt] [PATCH 2/4] Try harder to send RPC error message back to client



On Tue, Aug 17, 2010 at 11:16:33AM -0400, Daniel P. Berrange wrote:
> When failing to serialize the normal RPC reply, try harder to
> send a error message back to the client, instead of immediately
> closing the connection.
> 
> * daemon/dispatch.c: Improve error messages when RPC reply
>   can not be sent
> ---
>  daemon/dispatch.c |   47 +++++++++++++++++++++++++++++------------------
>  1 files changed, 29 insertions(+), 18 deletions(-)
> 
> diff --git a/daemon/dispatch.c b/daemon/dispatch.c
> index d6c2eb1..22eef36 100644
> --- a/daemon/dispatch.c
> +++ b/daemon/dispatch.c
> @@ -548,7 +548,8 @@ remoteDispatchClientCall (struct qemud_server *server,
>  
>      if (remoteEncodeClientMessageHeader(msg) < 0) {
>          xdr_free (data->ret_filter, (char*)&ret);
> -        goto fatal_error;
> +        remoteDispatchFormatError(&rerr, "%s", _("failed to serialize reply header"));
> +        goto xdr_hdr_error;
>      }
>  
>  
> @@ -558,22 +559,30 @@ remoteDispatchClientCall (struct qemud_server *server,
>                     msg->bufferLength,
>                     XDR_ENCODE);
>  
> -    if (xdr_setpos(&xdr, msg->bufferOffset) == 0)
> -        goto xdr_error;
> +    if (xdr_setpos(&xdr, msg->bufferOffset) == 0) {
> +        remoteDispatchFormatError(&rerr, "%s", _("failed to change XDR reply offset"));
> +	goto xdr_error;
> +    }
>  
>      /* If OK, serialise return structure, if error serialise error. */
>      /* Serialise reply data */
> -    if (!((data->ret_filter) (&xdr, &ret)))
> +    if (!((data->ret_filter) (&xdr, &ret))) {
> +        remoteDispatchFormatError(&rerr, "%s", _("failed to serialize reply payload (probable message size limit)"));
>          goto xdr_error;
> +    }
>  
>      /* Update the length word. */
>      msg->bufferOffset += xdr_getpos (&xdr);
>      len = msg->bufferOffset;
> -    if (xdr_setpos (&xdr, 0) == 0)
> +    if (xdr_setpos (&xdr, 0) == 0) {
> +        remoteDispatchFormatError(&rerr, "%s", _("failed to change XDR reply offset"));
>          goto xdr_error;
> +    }
>  
> -    if (!xdr_u_int (&xdr, &len))
> +    if (!xdr_u_int (&xdr, &len)) {
> +        remoteDispatchFormatError(&rerr, "%s", _("failed to update reply length header"));
>          goto xdr_error;
> +    }
>  
>      xdr_destroy (&xdr);
>      xdr_free (data->ret_filter, (char*)&ret);
> @@ -588,25 +597,27 @@ remoteDispatchClientCall (struct qemud_server *server,
>  
>      return 0;
>  
> +xdr_error:
> +    /* Bad stuff serializing reply. Try to send a little info
> +     * back to client to assist in bug reporting/diagnosis */
> +    xdr_free (data->ret_filter, (char*)&ret);
> +    xdr_destroy (&xdr);
> +    /* fallthrough */
> +
> +xdr_hdr_error:
> +    VIR_WARN("Failed to serialize reply for program '%d' proc '%d' as XDR",
> +	     msg->hdr.prog, msg->hdr.proc);
> +    /* fallthrough */
> +
>  rpc_error:
> -    /* Semi-bad stuff happened, we can still try to send back
> -     * an RPC error message to client */
> +    /* Bad stuff (de-)serializing message, but we have an
> +     * RPC error message we can send back to the client */
>      rv = remoteSerializeReplyError(client, &rerr, &msg->hdr);
>  
>      if (rv >= 0)
>          VIR_FREE(msg);
>  
>      return rv;
> -
> -xdr_error:
> -    /* Seriously bad stuff happened, so we'll kill off this client
> -       and not send back any RPC error */
> -    xdr_free (data->ret_filter, (char*)&ret);
> -    xdr_destroy (&xdr);
> -fatal_error:
> -    VIR_WARN("Failed to serialize reply for program '%d' proc '%d' as XDR",
> -	     msg->hdr.prog, msg->hdr.proc);
> -    return -1;
>  }

  ACK,

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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