RE: [RFC PATCH 6/6] Drivers: hv: vmbus: Refactor the ring-buffer iterator functions

["Michael Kelley \(LINUX\) via Virtualization" <virtualization@lists.linux-foundation.org>]

From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Wednesday, April 13, 2022 1:48 PM
> 
> With no users of hv_pkt_iter_next_raw() and no "external" users of
> hv_pkt_iter_first_raw(), the iterator functions can be refactored
> and simplified to remove some indirection/code.
> 
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
>  drivers/hv/ring_buffer.c | 11 +++++------
>  include/linux/hyperv.h   | 35 ++++-------------------------------
>  2 files changed, 9 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 3d215d9dec433..c9357dae2a2c8 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -421,7 +421,7 @@ int hv_ringbuffer_read(struct vmbus_channel *channel,
>  	memcpy(buffer, (const char *)desc + offset, packetlen);
> 
>  	/* Advance ring index to next packet descriptor */
> -	__hv_pkt_iter_next(channel, desc, true);
> +	__hv_pkt_iter_next(channel, desc);
> 
>  	/* Notify host of update */
>  	hv_pkt_iter_close(channel);
> @@ -459,7 +459,8 @@ static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info
> *rbi)
>  /*
>   * Get first vmbus packet without copying it out of the ring buffer
>   */
> -struct vmpacket_descriptor *hv_pkt_iter_first_raw(struct vmbus_channel *channel)
> +static struct vmpacket_descriptor *
> +hv_pkt_iter_first_raw(struct vmbus_channel *channel)
>  {
>  	struct hv_ring_buffer_info *rbi = &channel->inbound;
> 
> @@ -470,7 +471,6 @@ struct vmpacket_descriptor *hv_pkt_iter_first_raw(struct
> vmbus_channel *channel)
> 
>  	return (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi-
> >priv_read_index);
>  }
> -EXPORT_SYMBOL_GPL(hv_pkt_iter_first_raw);

Does hv_pkt_iter_first_raw() need to be retained at all as a
separate function?  I think after these changes, the only caller
is hv_pkt_iter_first(), in which case the code could just go
inline in hv_pkt_iter_first().  Doing that combining would
also allow the elimination of the duplicate call to 
hv_pkt_iter_avail().

Michael

> 
>  /*
>   * Get first vmbus packet from ring buffer after read_index
> @@ -534,8 +534,7 @@ EXPORT_SYMBOL_GPL(hv_pkt_iter_first);
>   */
>  struct vmpacket_descriptor *
>  __hv_pkt_iter_next(struct vmbus_channel *channel,
> -		   const struct vmpacket_descriptor *desc,
> -		   bool copy)
> +		   const struct vmpacket_descriptor *desc)
>  {
>  	struct hv_ring_buffer_info *rbi = &channel->inbound;
>  	u32 packetlen = desc->len8 << 3;
> @@ -548,7 +547,7 @@ __hv_pkt_iter_next(struct vmbus_channel *channel,
>  		rbi->priv_read_index -= dsize;
> 
>  	/* more data? */
> -	return copy ? hv_pkt_iter_first(channel) : hv_pkt_iter_first_raw(channel);
> +	return hv_pkt_iter_first(channel);
>  }
>  EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
> 
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 1112c5cf894e6..370adc9971d3e 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1673,55 +1673,28 @@ static inline u32 hv_pkt_len(const struct
> vmpacket_descriptor *desc)
>  	return desc->len8 << 3;
>  }
> 
> -struct vmpacket_descriptor *
> -hv_pkt_iter_first_raw(struct vmbus_channel *channel);
> -
>  struct vmpacket_descriptor *
>  hv_pkt_iter_first(struct vmbus_channel *channel);
> 
>  struct vmpacket_descriptor *
>  __hv_pkt_iter_next(struct vmbus_channel *channel,
> -		   const struct vmpacket_descriptor *pkt,
> -		   bool copy);
> +		   const struct vmpacket_descriptor *pkt);
> 
>  void hv_pkt_iter_close(struct vmbus_channel *channel);
> 
>  static inline struct vmpacket_descriptor *
> -hv_pkt_iter_next_pkt(struct vmbus_channel *channel,
> -		     const struct vmpacket_descriptor *pkt,
> -		     bool copy)
> +hv_pkt_iter_next(struct vmbus_channel *channel,
> +		 const struct vmpacket_descriptor *pkt)
>  {
>  	struct vmpacket_descriptor *nxt;
> 
> -	nxt = __hv_pkt_iter_next(channel, pkt, copy);
> +	nxt = __hv_pkt_iter_next(channel, pkt);
>  	if (!nxt)
>  		hv_pkt_iter_close(channel);
> 
>  	return nxt;
>  }
> 
> -/*
> - * Get next packet descriptor without copying it out of the ring buffer
> - * If at end of list, return NULL and update host.
> - */
> -static inline struct vmpacket_descriptor *
> -hv_pkt_iter_next_raw(struct vmbus_channel *channel,
> -		     const struct vmpacket_descriptor *pkt)
> -{
> -	return hv_pkt_iter_next_pkt(channel, pkt, false);
> -}
> -
> -/*
> - * Get next packet descriptor from iterator
> - * If at end of list, return NULL and update host.
> - */
> -static inline struct vmpacket_descriptor *
> -hv_pkt_iter_next(struct vmbus_channel *channel,
> -		 const struct vmpacket_descriptor *pkt)
> -{
> -	return hv_pkt_iter_next_pkt(channel, pkt, true);
> -}
> -
>  #define foreach_vmbus_pkt(pkt, channel) \
>  	for (pkt = hv_pkt_iter_first(channel); pkt; \
>  	    pkt = hv_pkt_iter_next(channel, pkt))
> --
> 2.25.1

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