* problem with function vlan_get_protocol()
@ 2011-07-17 4:53 jiangtao.jit
2011-07-17 7:34 ` Francois Romieu
2011-07-17 8:15 ` jiangtao.jit
0 siblings, 2 replies; 3+ messages in thread
From: jiangtao.jit @ 2011-07-17 4:53 UTC (permalink / raw)
To: netdev
Hi,all
in file inclue/linux/if_vlan.h
there is a statement in function vlan_get_protocol()
if (likely(protop))
protocol = *protop;
do we need an else branch on pointer protop failed ? through the else is unlikely
if (likely(protop))
protocol = *protop;
else
protocol = proto;
is it necessary ?
thanks
2011-07-17
jiangtao.jit
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: problem with function vlan_get_protocol()
2011-07-17 4:53 problem with function vlan_get_protocol() jiangtao.jit
@ 2011-07-17 7:34 ` Francois Romieu
2011-07-17 8:15 ` jiangtao.jit
1 sibling, 0 replies; 3+ messages in thread
From: Francois Romieu @ 2011-07-17 7:34 UTC (permalink / raw)
To: jiangtao.jit; +Cc: netdev
jiangtao.jit <jiangtao.jit@gmail.com> :
[...]
> do we need an else branch on pointer protop failed ? through the else is unlikely
>
> if (likely(protop))
> protocol = *protop;
> else
> protocol = proto;
>
> is it necessary ?
The else branch signals that skb_header_pointer uncloaked a really tiny
ethernet frame : the content of proto is not even initialized (stack
allocation), whence irrelevant. In such circumstances the default
initialization value of protocol (0) does not seem too bad.
--
Ueimor
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: problem with function vlan_get_protocol()
2011-07-17 4:53 problem with function vlan_get_protocol() jiangtao.jit
2011-07-17 7:34 ` Francois Romieu
@ 2011-07-17 8:15 ` jiangtao.jit
1 sibling, 0 replies; 3+ messages in thread
From: jiangtao.jit @ 2011-07-17 8:15 UTC (permalink / raw)
To: Francois Romieu; +Cc: netdev
Thanks a lot Francois
thank you for your explanation
--
jiangtao
发件人： Francois Romieu
发送时间： 2011-07-17 15:49:00
收件人： jiangtao.jit
抄送： netdev
主题： Re: problem with function vlan_get_protocol()
jiangtao.jit <jiangtao.jit@gmail.com> :
[...]
> do we need an else branch on pointer protop failed ? through the else is unlikely
>
> if (likely(protop))
> protocol = *protop;
> else
> protocol = proto;
>
> is it necessary ?
The else branch signals that skb_header_pointer uncloaked a really tiny
ethernet frame : the content of proto is not even initialized (stack
allocation), whence irrelevant. In such circumstances the default
initialization value of protocol (0) does not seem too bad.
--
Ueimor
^ permalink raw reply [flat|nested] 3+ messages in thread
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2011-07-17 7:34 ` Francois Romieu
2011-07-17 8:15 ` jiangtao.jit
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