netdev - Re: [PATCH RFC net-next 16/20] net/ipv6: Cleanup exception route handling

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Date:   Mon, 26 Feb 2018 13:25:37 -0700
From:   David Ahern <dsahern@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, idosch@...sch.org,
        roopa@...ulusnetworks.com, eric.dumazet@...il.com,
        weiwan@...gle.com, kafai@...com, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH RFC net-next 16/20] net/ipv6: Cleanup exception route
 handling

On 2/26/18 12:27 PM, David Miller wrote:
> From: David Ahern <dsahern@...il.com>
> Date: Sun, 25 Feb 2018 11:47:26 -0800
> 
>> IPv6 FIB will only contain FIB entries with exception routes added to
>> the FIB entry. Remove CACHE and dst checks from fib6 add and delete since
>> they can never happen once the data type changes.
>>
>> Fixup the lookup functions to use a f6i name for fib lookups and retain
>> the current rt name for return variables.
>>
>> Signed-off-by: David Ahern <dsahern@...il.com>
> 
> Hard to interpret what you mean in that second paragraph.
> 
> Do you mean that this invariant holds after patch #19 only?  Then you
> really can't make these simplifications until then in order to keep
> the patch series bisectable.
> 
> Otherwise you mean something else and I'd like to know what that is.
> 
> Either way, the commit message wording could be improved since even
> a dolt like me got confused :-)
> 

By the 20th iteration the description of the last few patches got a
little thin. ;-)

The point of patches 1-18 is to make as small a change per patch that
leads up to patch 19 being nothing more than s/rt6_info/fib6_info/ is
select data paths. A struct rename and all of the related code paths
makes for a huge patch.

Anyways, because rt6_info is used for both FIB and dst the lookup
functions can overload the rt6_info variable usually called 'rt'. This
patch introduces a new 'f6i' variable name for the result of the FIB
lookup and keeps 'rt' as the dst based return variable. 'f6i' becomes a
fib6_info in patch 19 which is why it is introduced as 'struct rt6_info
*f6i' now; avoids the additional churn in patch 19.