netdev - Re: [PATCH net-next] net: core: devlink: add new trap action HARD

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Message-ID: <AM0P190MB07387522928B6730DBE1BB77E4BD0@AM0P190MB0738.EURP190.PROD.OUTLOOK.COM>
Date:   Mon, 25 Jan 2021 12:24:27 +0000
From:   Oleksandr Mazur <oleksandr.mazur@...ision.eu>
To:     Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kuba@...nel.org>
CC:     Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jiri@...dia.com" <jiri@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: core: devlink: add new trap action
 HARD_DROP

Thu, Jan 21, 2021 at 06:36:05PM CET, kuba@...nel.org wrote:
>On Thu, 21 Jan 2021 14:21:52 +0200 Ido Schimmel wrote:
>> On Thu, Jan 21, 2021 at 01:29:37PM +0200, Oleksandr Mazur wrote:
>> > Add new trap action HARD_DROP, which can be used by the
>> > drivers to register traps, where it's impossible to get
>> > packet reported to the devlink subsystem by the device
>> > driver, because it's impossible to retrieve dropped packet
>> > from the device itself.
>> > In order to use this action, driver must also register
>> > additional devlink operation - callback that is used
>> > to retrieve number of packets that have been dropped by
>> > the device.  
>> 
>> Are these global statistics about number of packets the hardware dropped
>> for a specific reason or are these per-port statistics?
>> 
>> It's a creative use of devlink-trap interface, but I think it makes
>> sense. Better to re-use an existing interface than creating yet another
>> one.
>
>Not sure if I agree, if we can't trap why is it a trap?
>It's just a counter.

>+1
Device might be unable to trap only the 'DROP' packets, and this information should be transparent for the user.

I agree on the statement, that new action might be an overhead.
I could continue on with the solution Ido Schimmel proposed: since no new action would be needed and no UAPI changes are required, i could simply do the dropped statistics (additional field) output added upon trap stats queiring.
(In case if driver registerd callback, of course; and do so only for DROP actions)