Re: [libvirt] [PATCH 01/15] Defines the basics of a generic RPC protocol in XDR
On Thu, Dec 16, 2010 at 08:27:23AM -0700, Eric Blake wrote:
On 12/16/2010 04:21 AM, Daniel P. Berrange wrote:
> +const VIR_NET_MESSAGE_HEADER_MAX = 24;
> +
> +/* Size of message payload */
> +const VIR_NET_MESSAGE_PAYLOAD_MAX = 262120;
Would it be better to write VIR_NET_MESSAGE_PAYLOAD_MAX =
VIR_NET_MESSAGE_MAX - VIR_NET_MESSAGE_HEADER_MAX? But that's just cosmetic.
Unfortunately you can use expressions when defining
XDR constants.
> +
> +/* Size of message length field. Not counted in VIR_NET_MESSAGE_MAX */
> +const VIR_NET_MESSAGE_LEN_MAX = 4;
> +
> +const VIR_NET_MESSAGE_STRING_MAX = 65536;
You lost a useful comment from remote_protocol.h:
/* Length of long, but not unbounded, strings.
* This is an arbitrary limit designed to stop the decoder from trying
* to allocate unbounded amounts of memory when fed with a bad message.
*/
Yeah, I didn't even really want these bits of the protocol,
but backcompat for the error struct forced me to copy them
in.
> + * and the 'status' field varies according to:
> + *
> + * - type == VIR_NET_CALL
> + * * VIR_NET_OK always
> + *
> + * - type == VIR_NET_REPLY
> + * * VIR_NET_OK if RPC finished successfully
> + * * VIR_NET_ERROR if something failed
> + *
> + * - type == VIR_NET_MESSAGE
> + * * VIR_NET_OK always
> + *
> + * - type == VIR_NET_STREAM
> + * * VIR_NET_CONTINUE if more data is following
> + * * VIR_NET_OK if stream is complete
> + * * VIR_NET_ERROR if stream had an error
> + *
> + * Payload varies according to type and status:
> + *
> + * - type == VIR_NET_CALL
> + * XXX_args for procedure
> + *
> + * - type == VIR_NET_REPLY
> + * * status == VIR_NET_OK
> + * XXX_ret for procedure
> + * * status == VIR_NET_ERROR
> + * remote_error Error information
> + *
> + * - type == VIR_NET_MESSAGE
> + * * status == VIR_NET_OK
> + * XXX_args for procedure
> + * * status == VIR_NET_ERROR
> + * remote_error Error information
This is pure copy-and-paste from remote_protocol.x, but it doesnt' make
sense to me. Earlier, you said that VIR_NET_MESSAGE implies status is
VIR_NET_OK always, and that messages are asynchronous, rather than in
reply to a message. Either this should be:
- type == VIR_NET_MESSAGE
XXX_msg according to proc
Yeah that's the correct one. There are no errors associated
with async events.
or you need to allow for VIR_NET_MESSAGE to pass
status==VIR_NET_ERROR.
Daniel