netdev - Re: [PATCH v2 net-next 02/10] net: switchdev: remove the transaction structure from port object notifiers

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Message-ID: <20210106174202.GA1082997@shredder.lan>
Date:   Wed, 6 Jan 2021 19:42:02 +0200
From:   Ido Schimmel <idosch@...sch.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vadym Kochan <vkochan@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Jiri Pirko <jiri@...dia.com>, Ido Schimmel <idosch@...dia.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Ivan Vecera <ivecera@...hat.com>
Subject: Re: [PATCH v2 net-next 02/10] net: switchdev: remove the transaction
 structure from port object notifiers

On Wed, Jan 06, 2021 at 03:09:58PM +0200, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> Since the introduction of the switchdev API, port objects were
> transmitted to drivers for offloading using a two-step transactional
> model, with a prepare phase that was supposed to catch all errors, and a
> commit phase that was supposed to never fail.
> 
> Some classes of failures can never be avoided, like hardware access, or
> memory allocation. In the latter case, merely attempting to move the
> memory allocation to the preparation phase makes it impossible to avoid
> memory leaks, since commit 91cf8eceffc1 ("switchdev: Remove unused
> transaction item queue") which has removed the unused mechanism of
> passing on the allocated memory between one phase and another.
> 
> It is time we admit that separating the preparation from the commit
> phase is something that is best left for the driver to decide, and not
> something that should be baked into the API, especially since there are
> no switchdev callers that depend on this.
> 
> This patch removes the struct switchdev_trans member from switchdev port
> object notifier structures, and converts drivers to not look at this
> member.
> 
> Where driver conversion is trivial (like in the case of the Marvell
> Prestera driver, NXP DPAA2 switch, TI CPSW, and Rocker drivers), it is
> done in this patch.
> 
> Where driver conversion needs more attention (DSA, Mellanox Spectrum),
> the conversion is left for subsequent patches and here we only fake the
> prepare/commit phases at a lower level, just not in the switchdev
> notifier itself.
> 
> Where the code has a natural structure that is best left alone as a
> preparation and a commit phase (as in the case of the Ocelot switch),
> that structure is left in place, just made to not depend upon the
> switchdev transactional model.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> Acked-by: Linus Walleij <linus.walleij@...aro.org>
> Acked-by: Jiri Pirko <jiri@...dia.com>

This looks good to me. I think that faking the prepare/commit phase made
it easier to review.

Reviewed-by: Ido Schimmel <idosch@...dia.com>