Re: [PATCH 1/6] Drivers: hv: vmbus: Add utility function for querying ring size

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Feb 17, 2024 at 10:03:35AM -0800, Saurabh Sengar wrote:
> Add a function to query for the preferred ring buffer size of VMBus
> device.

That says what you did, but not why you did it.

> 
> Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> ---
>  drivers/hv/channel_mgmt.c | 7 +++++--
>  drivers/hv/hyperv_vmbus.h | 5 +++++
>  include/linux/hyperv.h    | 1 +
>  3 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 2f4d09ce027a..7ea444d72f9f 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -120,7 +120,8 @@ const struct vmbus_device vmbus_devs[] = {
>  	},
>  
>  	/* File copy */
> -	{ .dev_type = HV_FCOPY,
> +	{ .pref_ring_size = 0x4000,
> +	  .dev_type = HV_FCOPY,
>  	  HV_FCOPY_GUID,
>  	  .perf_device = false,
>  	  .allowed_in_isolated = false,
> @@ -141,11 +142,13 @@ const struct vmbus_device vmbus_devs[] = {
>  	},
>  
>  	/* Unknown GUID */
> -	{ .dev_type = HV_UNKNOWN,
> +	{ .pref_ring_size = 0x11000,
> +	  .dev_type = HV_UNKNOWN,

Where do these magic numbers for the size come from?

>  	  .perf_device = false,
>  	  .allowed_in_isolated = false,
>  	},
>  };
> +EXPORT_SYMBOL_GPL(vmbus_devs);
>  
>  static const struct {
>  	guid_t guid;
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index f6b1e710f805..76ac5185a01a 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -417,6 +417,11 @@ static inline bool hv_is_perf_channel(struct vmbus_channel *channel)
>  	return vmbus_devs[channel->device_id].perf_device;
>  }
>  
> +static inline size_t hv_dev_ring_size(struct vmbus_channel *channel)
> +{
> +	return vmbus_devs[channel->device_id].pref_ring_size;
> +}
> +
>  static inline bool hv_is_allocated_cpu(unsigned int cpu)
>  {
>  	struct vmbus_channel *channel, *sc;
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 2b00faf98017..5951c7bb5712 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -800,6 +800,7 @@ struct vmbus_requestor {
>  #define VMBUS_RQST_RESET (U64_MAX - 3)
>  
>  struct vmbus_device {
> +	size_t pref_ring_size;

No documentation for this?  What is the size in units of?

thanks,

greg k-h