RE: [PATCH 03/17] Drivers: hv: kvp: Cleanup error handling in KVP

[KY Srinivasan]

> -----Original Message-----
> From: Ben Hutchings [mailto:ben@xxxxxxxxxxxxxxx]
> Sent: Tuesday, July 24, 2012 9:11 PM
> To: KY Srinivasan
> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxx; olaf@xxxxxxxxx;
> apw@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 03/17] Drivers: hv: kvp: Cleanup error handling in KVP
> 
> On Tue, 2012-07-24 at 09:01 -0700, K. Y. Srinivasan wrote:
> > In preparation to implementing IP injection, cleanup the way we propagate
> > and handle errors both in the driver as well as in the user level daemon.
> >
> > Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> > Reviewed-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> > ---
> >  drivers/hv/hv_kvp.c      |  112 +++++++++++++++++++++++++++++++++++++-
> --------
> >  include/linux/hyperv.h   |   17 +++++---
> >  tools/hv/hv_kvp_daemon.c |   70 +++++++++++++++-------------
> >  3 files changed, 138 insertions(+), 61 deletions(-)
> >
> > diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
> > index 0012eed..9b7fc4a 100644
> > --- a/drivers/hv/hv_kvp.c
> > +++ b/drivers/hv/hv_kvp.c
> [...]
> > @@ -109,27 +154,52 @@ kvp_cn_callback(struct cn_msg *msg, struct
> netlink_skb_parms *nsp)
> >  {
> >  	struct hv_kvp_msg *message;
> >  	struct hv_kvp_msg_enumerate *data;
> > +	int	error = 0;
> >
> >  	message = (struct hv_kvp_msg *)msg->data;
> > -	switch (message->kvp_hdr.operation) {
> > +
> > +	/*
> > +	 * If we are negotiating the version information
> > +	 * with the daemon; handle that first.
> > +	 */
> > +
> > +	if (in_hand_shake) {
> > +		if (kvp_handle_handshake(message))
> > +			in_hand_shake = false;
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * Based on the version of the daemon, we propagate errors from the
> > +	 * daemon differently.
> > +	 */
> > +
> > +	data = &message->body.kvp_enum_data;
> > +
> > +	switch (dm_reg_value) {
> >  	case KVP_OP_REGISTER:
> > -		pr_info("KVP: user-mode registering done.\n");
> > -		kvp_register();
> > -		kvp_transaction.active = false;
> > -		hv_kvp_onchannelcallback(kvp_transaction.kvp_context);
> > +		/*
> > +		 * Null string is used to pass back error condition.
> > +		 */
> > +		if (!strlen(data->data.key))
> 
> Do we know that the key is null-terminated here?  Shouldn't we just
> check whether data->data.key[0] == 0?

Yes, currently we do return null string to indicate error.

> 
> > +			error = HV_S_CONT;
> >  		break;
> >
> > -	default:
> > -		data = &message->body.kvp_enum_data;
> > +	case KVP_OP_REGISTER1:
> >  		/*
> > -		 * Complete the transaction by forwarding the key value
> > -		 * to the host. But first, cancel the timeout.
> > +		 * We use the message header information from
> > +		 * the user level daemon to transmit errors.
> >  		 */
> > -		if (cancel_delayed_work_sync(&kvp_work))
> > -			kvp_respond_to_host(data->data.key,
> > -					 data->data.value,
> > -					!strlen(data->data.key));
> > +		error = *((int *)(&message->kvp_hdr.operation));
> [...]
> 
> What's with the casting (repeated in many other places)?  Wouldn't it be
> better to redefine struct hv_kvp_msg to start with something like:
> 
> 	union {
> 		struct hv_kvp_hdr	request;
> 		int			error;
> 	} kvp_hdr;

Agreed; will do.
> 
> Ben.
> 
> --
> Ben Hutchings
> If more than one person is responsible for a bug, no one is at fault.
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