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* 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
end of thread, other threads:[~2011-07-17  8:16 UTC | newest]

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