Re: [dpdk-dev] [PATCH v6 8/8] rte_ethdev.h: align sign and scope of temp var

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, May 21, 2018 at 10:01:33AM +0800, Andy Green wrote:
> /projects/lagopus/src/dpdk/build/include/rte_ethdev.h:
> In function 'rte_eth_rx_burst':
> /projects/lagopus/src/dpdk/build/include/rte_ethdev.h:
> 3836:18: warning: conversion to 'int16_t' {aka 'short
> int'} from 'uint16_t' {aka 'short unsigned int'} may
> change the sign of the result [-Wsign-conversion]
>   int16_t nb_rx = (*dev->rx_pkt_burst)(dev->data->
> rx_queues[queue_id],
>                   ^
> /projects/lagopus/src/dpdk/build/include/rte_ethdev.h:
> 3844:50: warning: conversion to 'uint16_t' {aka 'short
> unsigned int'} from 'int16_t' {aka 'short int'} may
> change the sign of the result [-Wsign-conversion]
>     nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
>                                                   ^~~~~
> /projects/lagopus/src/dpdk/build/include/rte_ethdev.h:
> 3844:12: warning: conversion to 'int16_t' {aka 'short
> int'} from 'uint16_t' {aka 'short unsigned int'} may
> change the sign of the result [-Wsign-conversion]
>     nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
>             ^~
> /projects/lagopus/src/dpdk/build/include/rte_ethdev.h:
> 3851:9: warning: conversion to 'uint16_t' {aka 'short
> unsigned int'} from 'int16_t' {aka 'short int'} may
> change the sign of the result [-Wsign-conversion]
>   return nb_rx;
>          ^~~~~
> 
> The second part of the patch is solved by its own basic
> block because it is inside a preprocessor conditional.
> 
> Bringing the declaration of the var to the top of the
> function would require that also being given its own
> preprocessor conditional, or a (void)var to avoid an
> unused var warning.  The basic block is no worse than
> those imho.
> 
> Signed-off-by: Andy Green <andy@warmcat.com>
> ---
>  lib/librte_ethdev/rte_ethdev.h |   25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
> index d52c1bed9..4d059a2a7 100644
> --- a/lib/librte_ethdev/rte_ethdev.h
> +++ b/lib/librte_ethdev/rte_ethdev.h
> @@ -3823,6 +3823,7 @@ rte_eth_rx_burst(uint16_t port_id, uint16_t queue_id,
>  		 struct rte_mbuf **rx_pkts, const uint16_t nb_pkts)
>  {
>  	struct rte_eth_dev *dev = &rte_eth_devices[port_id];
> +	uint16_t nb_rx;
>  
>  #ifdef RTE_LIBRTE_ETHDEV_DEBUG
>  	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, 0);
> @@ -3833,18 +3834,22 @@ rte_eth_rx_burst(uint16_t port_id, uint16_t queue_id,
>  		return 0;
>  	}
>  #endif
> -	int16_t nb_rx = (*dev->rx_pkt_burst)(dev->data->rx_queues[queue_id],
> -			rx_pkts, nb_pkts);
> +	nb_rx = (*dev->rx_pkt_burst)(dev->data->rx_queues[queue_id],
> +				     rx_pkts, nb_pkts);
>  
>  #ifdef RTE_ETHDEV_RXTX_CALLBACKS
> -	struct rte_eth_rxtx_callback *cb = dev->post_rx_burst_cbs[queue_id];
> -
> -	if (unlikely(cb != NULL)) {
> -		do {
> -			nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
> -						nb_pkts, cb->param);
> -			cb = cb->next;
> -		} while (cb != NULL);
> +	{
> +		struct rte_eth_rxtx_callback *cb =
> +				dev->post_rx_burst_cbs[queue_id];
> +
> +		if (unlikely(cb != NULL)) {
> +			do {
> +				nb_rx = cb->fn.rx(port_id, queue_id,
> +						  rx_pkts, nb_rx,
> +						  nb_pkts, cb->param);
> +				cb = cb->next;
> +			} while (cb != NULL);
> +		}
>  	}

I think you can eliminate these extra brackets by moving the cb declaration
inside the if body:

if (unlikely(dev->post_rx_burst_cbs[queue_id] != NULL)) {$
	struct rte_eth_rxtx_callback *cb =
			dev->post_rx_burst_cbs[queue_id];
	do {$
		nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,$
				nb_pkts, cb->param);$
		cb = cb->next;$
	} while (cb != NULL);$
}

/Bruce