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Date:   Sun, 13 May 2018 10:24:09 -0700
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     kys@linuxonhyperv.com
Cc:     kys@microsoft.com, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, devel@linuxdriverproject.org,
        olaf@aepfle.de, apw@canonical.com, jasowang@redhat.com,
        vkuznets@redhat.com, Stephen Hemminger <sthemmin@microsoft.com>,
        Michael Kelley <mikelley@microsoft.com>
Subject: Re: [PATCH 1/1] Drivers: hv: vmbus: enable VMBus protocol version
 5.0
Message-ID: <20180513102409.4adc5200@xeon-e3>
In-Reply-To: <20180512093033.12325-1-kys@linuxonhyperv.com>
References: <20180512093033.12325-1-kys@linuxonhyperv.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Sat, 12 May 2018 02:30:33 -0700
kys@linuxonhyperv.com wrote:

>  int vmbus_post_msg(void *buffer, size_t buflen, bool can_sleep)
>  {
> +	struct vmbus_channel_message_header *hdr;
>  	union hv_connection_id conn_id;
>  	int ret = 0;
>  	int retries = 0;
>  	u32 usec = 1;
>  
>  	conn_id.asu32 = 0;
> -	conn_id.u.id = VMBUS_MESSAGE_CONNECTION_ID;
> +	conn_id.u.id = vmbus_connection.msg_conn_id;
>  
>  	/*
>  	 * hv_post_message() can have transient failures because of
> @@ -372,6 +400,18 @@ int vmbus_post_msg(void *buffer, size_t buflen, bool can_sleep)
>  
>  		switch (ret) {
>  		case HV_STATUS_INVALID_CONNECTION_ID:
> +			/*
> +			 * See vmbus_negotiate_version(): VMBus protocol 5.0
> +			 * requires that we must use
> +			 * VMBUS_MESSAGE_CONNECTION_ID_4 for the Initiate
> +			 * Contact message, but on old hosts that only
> +			 * support VMBus protocol 4.0 or lower, here we get
> +			 * HV_STATUS_INVALID_CONNECTION_ID and we should
> +			 * return an error immediately without retrying.
> +			 */
> +			hdr = (struct vmbus_channel_message_header *)buffer;

Hate to pick o the details, but buffer is void * so cast is not necessary here.