netdev - Re: [PATCH net-next v1 0/5] Devlink reload and missed notifications fix

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Message-ID: <20210929073940.5d7ed022@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 29 Sep 2021 07:39:40 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>, Ariel Elior <aelior@...vell.com>,
        Bin Luo <luobin9@...wei.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Coiby Xu <coiby.xu@...il.com>,
        Derek Chickles <dchickles@...vell.com>, drivers@...sando.io,
        Eric Dumazet <eric.dumazet@...il.com>,
        Felix Manlunas <fmanlunas@...vell.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Geetha sowjanya <gakula@...vell.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        GR-everest-linux-l2@...vell.com, GR-Linux-NIC-Dev@...vell.com,
        hariprasad <hkelam@...vell.com>,
        Ido Schimmel <idosch@...dia.com>,
        intel-wired-lan@...ts.osuosl.org,
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        Linu Cherian <lcherian@...vell.com>,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-staging@...ts.linux.dev,
        Manish Chopra <manishc@...vell.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Moshe Shemesh <moshe@...dia.com>, netdev@...r.kernel.org,
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        Richard Cochran <richardcochran@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
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        UNGLinuxDriver@...rochip.com, Vadym Kochan <vkochan@...vell.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Yisen Zhuang <yisen.zhuang@...wei.com>
Subject: Re: [PATCH net-next v1 0/5] Devlink reload and missed notifications
 fix

On Wed, 29 Sep 2021 17:13:28 +0300 Leon Romanovsky wrote:
> On Wed, Sep 29, 2021 at 06:40:04AM -0700, Jakub Kicinski wrote:
> > On Wed, 29 Sep 2021 15:00:41 +0300 Leon Romanovsky wrote:  
> > > This series starts from the fixing the bug introduced by implementing
> > > devlink delayed notifications logic, where I missed some of the
> > > notifications functions.
> > > 
> > > The rest series provides a way to dynamically set devlink ops that is
> > > needed for mlx5 multiport device and starts cleanup by removing
> > > not-needed logic.
> > > 
> > > In the next series, we will delete various publish API, drop general
> > > lock, annotate the code and rework logic around devlink->lock.
> > > 
> > > All this is possible because driver initialization is separated from the
> > > user input now.  
> > 
> > Swapping ops is a nasty hack in my book.
> > 
> > And all that to avoid having two op structures in one driver.
> > Or to avoid having counters which are always 0?  
> 
> We don't need to advertise counters for feature that is not supported.
> In multiport mlx5 devices, the reload functionality is not supported, so
> this change at least make that device to behave like all other netdev
> devices that don't support devlink reload.
> 
> The ops structure is set very early to make sure that internal devlink
> routines will be able access driver back during initialization (btw very
> questionable design choice)

Indeed, is this fixable? Or now that devlink_register() was moved to 
the end of probe netdev can call ops before instance is registered?

> and at that stage the driver doesn't know
> yet which device type it is going to drive.
> 
> So the answer is:
> 1. Can't have two structures.

I still don't understand why. To be clear - swapping full op structures
is probably acceptable if it's a pure upgrade (existing pointers match).
Poking new ops into a structure (in alphabetical order if I understand
your reply to Greg, not destructor-before-contructor) is what I deem
questionable.

> 2. Same behaviour across all netdev devices.

Unclear what this is referring to.