Date: Thu, 1 Dec 2016 21:35:47 +0100
From: Greg KH <gregkh@linuxfoundation.org>
To: kys@microsoft.com
Cc: linux-kernel@vger.kernel.org, devel@linuxdriverproject.org,
        olaf@aepfle.de, apw@canonical.com, vkuznets@redhat.com,
        jasowang@redhat.com, leann.ogasawara@canonical.com,
        Haiyang Zhang <haiyangz@microsoft.com>
Subject: Re: [PATCH 02/15] hyperv: Add a function to detect hv_device
Message-ID: <20161201203547.GB1602@kroah.com>
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On Thu, Dec 01, 2016 at 09:28:39AM -0800, kys@exchange.microsoft.com wrote:
> From: Haiyang Zhang <haiyangz@microsoft.com>
> 
> Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> ---
>  drivers/hv/vmbus_drv.c |    6 ++++++
>  include/linux/hyperv.h |    2 ++
>  2 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 0276d2e..1730ac0 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -692,6 +692,12 @@ struct onmessage_work_context {
>  	struct hv_message msg;
>  };
>  
> +bool device_is_hyperv(struct device *dev)
> +{
> +	return dev->release == vmbus_device_release;
> +}
> +EXPORT_SYMBOL_GPL(device_is_hyperv);

Wait, eek, no!  That's NOT how you determine a device type, if you
really even ever need to do that.

Why are you needing this?  You should always "just know" what type of
device a struct device * is, that's what we rely on in the driver model.
Otherwise things get messy very very quickly.

Sorry, I can't take this without a ton of justification, and even then,
you need to do this correctly (and no, I'm not going to tell you how to
do that as I don't like it being done...)

greg k-h