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

KY Srinivasan
2012-07-25T14:10:37Z

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> -----Original Message-----
> From: Ben Hutchings [mailto:ben@decadent.org.uk]
> Sent: Tuesday, July 24, 2012 9:11 PM
> To: KY Srinivasan
> Cc: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org;
> devel@linuxdriverproject.org; virtualization@lists.osdl.org; olaf@aepfle.de;
> apw@canonical.com; netdev@vger.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@microsoft.com>
> > Reviewed-by: Haiyang Zhang <haiyangz@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?

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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