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Date: Wed, 12 Oct 2016 21:01:54 +0800 From: zhuyj <zyjzyj2000@...il.com> To: Jiri Benc <jbenc@...hat.com> Cc: netdev <netdev@...r.kernel.org>, pabeni@...hat.com, daniel@...earbox.net, Pravin B Shelar <pshelar@...ira.com>, Alexander Duyck <aduyck@...antis.com>, hannes@...essinduktion.org, "David S. Miller" <davem@...emloft.net> Subject: Re: [PATCH 1/1] vxlan: insert ipv6 macro Hi, Jiri How to explain the following source code? As you mentioned, are the #ifdefs in the following source pointless? As to the previous patch, I will compile and analyze it. But now I am busy with something else. After I draw a conclusion, I will let you know. Thanks for your reply. static void vxlan_sock_release(struct vxlan_dev *vxlan) { bool ipv4 = __vxlan_sock_release_prep(vxlan->vn4_sock); #if IS_ENABLED(CONFIG_IPV6) bool ipv6 = __vxlan_sock_release_prep(vxlan->vn6_sock); #endif synchronize_net(); if (ipv4) { udp_tunnel_sock_release(vxlan->vn4_sock->sock); kfree(vxlan->vn4_sock); } #if IS_ENABLED(CONFIG_IPV6) if (ipv6) { udp_tunnel_sock_release(vxlan->vn6_sock->sock); kfree(vxlan->vn6_sock); } #endif } On Tue, Oct 11, 2016 at 10:06 PM, Jiri Benc <jbenc@...hat.com> wrote: > On Tue, 11 Oct 2016 16:23:31 +0800, zyjzyj2000@...il.com wrote: >> --- a/drivers/net/vxlan.c >> +++ b/drivers/net/vxlan.c >> @@ -2647,15 +2647,15 @@ static struct socket *vxlan_create_sock(struct net *net, bool ipv6, >> int err; >> >> memset(&udp_conf, 0, sizeof(udp_conf)); >> - >> +#if IS_ENABLED(CONFIG_IPV6) >> if (ipv6) { >> udp_conf.family = AF_INET6; >> udp_conf.use_udp6_rx_checksums = >> !(flags & VXLAN_F_UDP_ZERO_CSUM6_RX); >> udp_conf.ipv6_v6only = 1; >> - } else { >> + } else >> +#endif >> udp_conf.family = AF_INET; >> - } > > Zhu Yanjun, before posting patches such as the previous ones or > this one, please test whether they make any difference. In this case, > try to compile the code with IPv6 disabled before and after this patch, > disassemble and compare the results. You'll see that this patch is > pointless. > > It's pretty obvious from the code but to be really sure, I've just > quickly built the vxlan module with IPv6 disabled. And indeed, as > expected, the compiler just inlined everything into vxlan_open. The > whole chain vxlan_open -> vxlan_sock_add -> __vxlan_sock_add (note that > there's only a single caller of __vxlan_sock_add with IPv6 disabled) -> > vxlan_socket_create -> vxlan_create_sock is inlined. > > It also means the code in the "if (ipv6)" branch is completely > eliminated by the compiler even without ugly #ifdefs. > > Jiri
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