linux-kernel - Re: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs

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Date:	Mon, 21 Mar 2016 09:29:12 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
	jasowang@...hat.com
Subject: Re: [PATCH 5/5] Drivers: hv: vmbus: Implement copy-free read APIs

"K. Y. Srinivasan" <kys@...rosoft.com> writes:

> Implement copy-free read APIs.
>
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> ---
>  drivers/hv/ring_buffer.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/hyperv.h   |    6 +++++
>  2 files changed, 61 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index c2c2b2e..c80e1f3 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -444,3 +444,58 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
>
>  	return ret;
>  }
> +
> +/*
> + * In-place read functions.
> + */
> +bool get_next_pkt_raw(struct vmbus_channel *channel,
> +		      struct vmpacket_descriptor **desc)

I suggest we make these functions return pointers and use
ERR_PTR()/IS_ERR() when we need to return an error.

> +{
> +	struct hv_ring_buffer_info *ring_info = &channel->inbound;
> +	u32 read_loc = ring_info->ring_buffer->read_index;
> +	void *ring_buffer = hv_get_ring_buffer(ring_info);
> +	struct vmpacket_descriptor *cur_desc;
> +	u32 packetlen;
> +	u32 dsize = ring_info->ring_datasize;
> +	u32 bytes_avail_toread = hv_get_bytes_to_read(ring_info);
> +
> +	if (bytes_avail_toread < sizeof(struct vmpacket_descriptor))
> +		return false;
> +
> +	if ((read_loc + sizeof(*desc)) > dsize)
> +		return false;
> +
> +	cur_desc = ring_buffer + read_loc;
> +	packetlen = cur_desc->len8 << 3;
> +
> +	if ((read_loc + packetlen + 8) > (dsize - 1))

Could you please add a define for this '8'?


> +		return false;
> +
> +	*desc = cur_desc;
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(get_next_pkt_raw);
> +
> +void put_pkt_raw(struct vmbus_channel *channel,
> +		 struct vmpacket_descriptor *desc)
> +{
> +	struct hv_ring_buffer_info *ring_info = &channel->inbound;
> +	u32 read_loc = ring_info->ring_buffer->read_index;
> +	u32 packetlen = desc->len8 << 3;
> +	u32 dsize = ring_info->ring_datasize;
> +
> +	if ((read_loc + packetlen + 8) > dsize)
> +		BUG();
> +
> +	/*
> +	 * Make sure all reads are done before we update the read index since
> +	 * the writer may start writing to the read area once the read index
> +	 * is updated.
> +	 */
> +	virt_mb();
> +	ring_info->ring_buffer->read_index += packetlen + 8;
> +
> +	if (hv_need_to_signal_on_read(ring_info))
> +		vmbus_set_event(channel);
> +}
> +EXPORT_SYMBOL_GPL(put_pkt_raw);
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index a6b053c..455f3f0 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1035,6 +1035,12 @@ extern int vmbus_recvpacket_raw(struct vmbus_channel *channel,
>  				     u32 *buffer_actual_len,
>  				     u64 *requestid);
>
> +bool get_next_pkt_raw(struct vmbus_channel *channel,
> +		      struct vmpacket_descriptor **desc);
> +
> +void put_pkt_raw(struct vmbus_channel *channel,
> +		 struct vmpacket_descriptor *desc);
> +
>
>  extern void vmbus_ontimer(unsigned long data);

-- 
  Vitaly