netdev - Re: [PATCH] pktgen: avoid unused-const-variable warning

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Message-ID: <4c260b13-3b08-409d-a88a-e5bbb3c18e03@redhat.com>
Date: Thu, 27 Feb 2025 12:35:45 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Peter Seiderer <ps.report@....net>, Arnd Bergmann <arnd@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Arnd Bergmann <arnd@...db.de>, Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pktgen: avoid unused-const-variable warning

On 2/26/25 7:17 PM, Peter Seiderer wrote:
> From: Arnd Bergmann <arnd@...db.de>
>> When extra warnings are enable, there are configurations that build
>> pktgen without CONFIG_XFRM, which leaves a static const variable unused:
>>
>> net/core/pktgen.c:213:1: error: unused variable 'F_IPSEC' [-Werror,-Wunused-const-variable]
>>   213 | PKT_FLAGS
>>       | ^~~~~~~~~
>> net/core/pktgen.c:197:2: note: expanded from macro 'PKT_FLAGS'
>>   197 |         pf(IPSEC)               /* ipsec on for flows */                \
>>       |         ^~~~~~~~~
>>
>> This could be marked as __maybe_unused, or by making the one use visible
>> to the compiler by slightly rearranging the #ifdef blocks. The second
>> variant looks slightly nicer here, so use that.
>>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>  net/core/pktgen.c | 9 ++-------
>>  1 file changed, 2 insertions(+), 7 deletions(-)
>>
>> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
>> index 55064713223e..402e01a2ce19 100644
>> --- a/net/core/pktgen.c
>> +++ b/net/core/pktgen.c
>> @@ -158,9 +158,7 @@
>>  #include <net/udp.h>
>>  #include <net/ip6_checksum.h>
>>  #include <net/addrconf.h>
>> -#ifdef CONFIG_XFRM
>>  #include <net/xfrm.h>
>> -#endif
> 
> This ifdef/endif can be kept (as the xfrm stuff is still not used)...

FTR, I think dropping unneeded #ifdef is preferable in c files: only
such file build time is affected, and the code is more readable.

> 
>>  #include <net/netns/generic.h>
>>  #include <asm/byteorder.h>
>>  #include <linux/rcupdate.h>
>> @@ -2363,13 +2361,13 @@ static inline int f_pick(struct pktgen_dev *pkt_dev)
>>  }
>>
>>
>> -#ifdef CONFIG_XFRM
>>  /* If there was already an IPSEC SA, we keep it as is, else
>>   * we go look for it ...
>>  */
>>  #define DUMMY_MARK 0
> 
> A now unused define...
> 
>>  static void get_ipsec_sa(struct pktgen_dev *pkt_dev, int flow)
>>  {
>> +#ifdef CONFIG_XFRM
>>  	struct xfrm_state *x = pkt_dev->flows[flow].x;
>>  	struct pktgen_net *pn = net_generic(dev_net(pkt_dev->odev), pg_net_id);
> 
> Maybe better this way here?

I think the unused define is preferable; I think pre-processor defines
are cheaper than static const.

Thanks,

Paolo