linux-kernel - Re: [PATCH 03/17] Drivers: hv: kvp: Cleanup error handling in KVP

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Date:	Wed, 25 Jul 2012 02:10:44 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, virtualization@...ts.osdl.org,
	olaf@...fle.de, apw@...onical.com, netdev@...r.kernel.org
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@...rosoft.com>
> Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
> ---
>  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?

> +			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;

Ben.

-- 
Ben Hutchings
If more than one person is responsible for a bug, no one is at fault.

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