netdev - Re: [RFC iproute2-next 00/11] ip: nexthop: cache nexthops and print routes' nh info

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Date:   Thu, 30 Sep 2021 10:17:03 +0300
From:   Nikolay Aleksandrov <razor@...ckwall.org>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Cc:     roopa@...dia.com, donaldsharp72@...il.com, idosch@...sch.org,
        Nikolay Aleksandrov <nikolay@...dia.com>
Subject: Re: [RFC iproute2-next 00/11] ip: nexthop: cache nexthops and print
 routes' nh info

On 30/09/2021 06:42, David Ahern wrote:
> On 9/29/21 9:28 AM, Nikolay Aleksandrov wrote:
>> From: Nikolay Aleksandrov <nikolay@...dia.com>
>>
>> Hi,
>> This set tries to help with an old ask that we've had for some time
>> which is to print nexthop information while monitoring or dumping routes.
>> The core problem is that people cannot follow nexthop changes while
>> monitoring route changes, by the time they check the nexthop it could be
>> deleted or updated to something else. In order to help them out I've
>> added a nexthop cache which is populated (only used if -d / show_details
>> is specified) while decoding routes and kept up to date while monitoring.
>> The nexthop information is printed on its own line starting with the
>> "nh_info" attribute and its embedded inside it if printing JSON. To
>> cache the nexthop entries I parse them into structures, in order to
>> reuse most of the code the print helpers have been altered so they rely
>> on prepared structures. Nexthops are now always parsed into a structure,
>> even if they won't be cached, that structure is later used to print the
>> nexthop and destroyed if not going to be cached. New nexthops (not found
>> in the cache) are retrieved from the kernel using a private netlink
>> socket so they don't disrupt an ongoing dump, similar to how interfaces
>> are retrieved and cached.
>>
>> I have tested the set with the kernel forwarding selftests and also by
>> stressing it with nexthop create/update/delete in loops while monitoring.
>>
>> Comments are very welcome as usual. :)
> 
> overall it looks fine and not surprised a cache is needed.
> 
> Big comment is to re-order the patches - do all of the refactoring first
> to get the code where you need it and then add what is needed for the cache.
> 

Thanks for the comments, apart from pairing the add parse/use parse functions
in the first few patches only patch 08 seems out of place, although it's there
because it was first needed in patch 09, I don't mind pulling it back.
All other patches after 06 are adding the new cache and print functions and
using them in iproute/ipmonitor, there is no refactoring done in those, so I
plan to keep those as they are.

Cheers,
 Nik