Re: [dpdk-dev] [PATCH V2 1/3] net: avoid cast-align warning in VLAN insert function

[Eli Britstein <elibr@nvidia.com>]

On 10/21/2021 6:48 PM, Stephen Hemminger wrote:
> External email: Use caution opening links or attachments
>
>
> On Thu, 21 Oct 2021 11:51:30 +0300
> Eli Britstein <elibr@nvidia.com> wrote:
>
>> In rte_vlan_insert there is a casting of rte_pktmbuf_prepend returned
>> value to (struct rte_ether_hdr *), which causes cast-align warning when
>> using strict cast align flag with supporting gcc:
>> gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
>> CFLAGS="-Wcast-align=strict" make V=1 -C examples/l2fwd clean static
>>
>> In file included from main.c:35:
>> /dpdk/build/include/rte_ether.h:370:7: warning: cast increases required
>> alignment of target type [-Wcast-align]
>>    370 |  nh = (struct rte_ether_hdr *)
>>        |       ^
>>
>> As the code assumes correct alignment, add first a (void *) casting, to
>> avoid the warning.
>>
>> Fixes: c974021a5949 ("ether: add soft vlan encap/decap")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Eli Britstein <elibr@nvidia.com>
>> Acked-by: Olivier Matz <olivier.matz@6wind.com>
> After cast to void * the second cast is not necessary.
>
>          nh = (void *)rte_pktmbuf_prepend(...)
>
> Ideally rte_pktmbuf_prepend() should return void * but that is
> an API change.

Removing the second cast, it is silently done anyway, as 'nh' is of type 
'struct rte_ether_hdr *'.

Going with this approach (I can also do it for patch 3/3), we can change 
rte_pktmbuf_prepend to return (void *), and let the applications using 
it do the silent cast.

What do you think?