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

[Ben Hutchings]

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 <k...@microsoft.com>
> Reviewed-by: Haiyang Zhang <haiya...@microsoft.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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