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

[Andy Green]

On 05/21/2018 09:30 PM, Bruce Richardson wrote:
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 <a...@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);$
}

Okay... it repeats the expression but what the hey.  It's changed to 
that in the v7 just pushed.

-Andy

/Bruce