linux-kernel - Re: [PATCH v2 05/13] can: slcan: simplify the device de-allocation

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Message-ID: <20220612182302.36bdd9b9.max@enpas.org>
Date:   Sun, 12 Jun 2022 18:23:02 +0200
From:   Max Staudt <max@...as.org>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     Oliver Hartkopp <socketcan@...tkopp.net>,
        linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Paolo Abeni <pabeni@...hat.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 05/13] can: slcan: simplify the device de-allocation

On Sat, 11 Jun 2022 12:46:04 +0200
Dario Binacchi <dario.binacchi@...rulasolutions.com> wrote:

> > As written before I would like to discuss this change out of your
> > patch series "can: slcan: extend supported features" as it is no
> > slcan feature extension AND has to be synchronized with the
> > drivers/net/slip/slip.c implementation.  
> 
> Why do you need to synchronize it with  drivers/net/slip/slip.c
> implementation ?

Because slcan.c is a derivative of slip.c and the code still looks
*very* similar, so improvements in one file should be ported to the
other and vice versa. This has happened several times now.

> > When it has not real benefit and introduces more code and may create
> > side effects, this beautification should probably be omitted at all.
> >  
> 
> I totally agree with you. I would have already dropped it if this
> patch didn't make sense. But since I seem to have understood that
> this is not the case, I do not understand why it cannot be improved
> in this series.

This series is mostly about adding netlink support. If there is a point
of contention about a beautification, it may be easier to discuss that
separately, so the netlink code can be merged while the beautification
is still being discussed.

On another note, the global array of slcan_devs is really unnecessary
and maintaining it is a mess - as seen in some of your patches, that
have to account for it in tons of places and get complicated because of
it.

slcan_devs is probably grandfathered from a very old kernel, since
slip.c is about 30 years old, so I suggest to remove it entirely. In
fact, it may be easier to patch slcan_devs away first, and that will
simplify your open/close patches - your decision :)

If you wish to implement the slcan_devs removal, here are some hints:

The private struct can just be allocated as part of struct can_priv in
slcan_open(), like so:

  struct net_device *dev;
  dev = alloc_candev(sizeof(struct slcan), 0);

And then accessed like so:

  struct slcan *sl = netdev_priv(dev);

Make sure to add struct can_priv as the first member of struct slcan:

  /* This must be the first member when using alloc_candev() */
  struct can_priv can;

> The cover letter highlighted positive reactions to the series because
> the module had been requiring these kinds of changes for quite
> some time. So, why not take the opportunity to finalize this patch in
> this series even if it doesn't extend the supported features ?

Because... I can only speak for myself, but I'd merge all the
unambiguous stuff first and discuss the difficult stuff later, if there
are no interdependencies :)

Max