Re: [PATCH net] net: sched: fix initialiser warning in sch_frag.c

On Mon, Sep 20, 2021 at 11:08:53AM +0200, Davide Caratti wrote:

On Sun, Sep 19, 2021 at 11:40:33PM +0100, Russell King (Oracle) wrote:

quoted

Debian gcc 10.2.1 complains thusly:

net/sched/sch_frag.c:93:10: warning: missing braces around initializer [-Wmissing-braces]
   struct rtable sch_frag_rt = { 0 };
          ^
net/sched/sch_frag.c:93:10: warning: (near initialization for 'sch_frag_rt.dst') [-Wmissing-braces]

Fix it by removing the unnecessary '0' initialiser, leaving the
braces.

hello Russell, thanks a lot for reporting!
 

quoted

diff --git a/net/sched/sch_frag.c b/net/sched/sch_frag.c
index 8c06381391d6..ab359d63287c 100644
--- a/net/sched/sch_frag.c
+++ b/net/sched/sch_frag.c

@@ -90,7 +90,7 @@ static int sch_fragment(struct net *net, struct sk_buff *skb,
 	}
 
 	if (skb_protocol(skb, true) == htons(ETH_P_IP)) {
-		struct rtable sch_frag_rt = { 0 };
+		struct rtable sch_frag_rt = { };

this surely fixes the -Wmissing-braces, but then -Wpedantic
would complain about usage of GNU extension (I just tried on godbolt
with x86_64 gcc 11.2):

warning: ISO C forbids empty initializer braces [-Wpedantic]

While we are fixing this, probably the best thing is to initialize the
'dst' struct member  to 0: in my understanding this should be sufficient
to let the compiler fill all the struct members with 0.

Oh, and I might have inserted a similar thing in openvswitch kernel
module (see [1]), if you agree I will send a patch that fixes this as
well. WDYT?

ISO C may forbid it, but the kernel build uses -std=gnu89 - which is
c89 with GNU extensions. One of the GNU extensions is to allow the
empty initialiser, which means "initialise all members of this struct
to zero".

However, as I say, this was found using gcc 4.9.4 under 5.14, where
4.9.4 is a permissable compiler. However, under 5.15-rc it is no
longer so the patch should not be applied to development kernels.
It leaves the question open whether it should be fixed in stable or
not, since stable kernels _do_ permit gcc 4.9.4.

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