linux-kernel - Re: [PATCH net-next] devlink: Set device as early as possible

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Date:   Tue, 10 Aug 2021 16:45:20 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Prabhakar Kushwaha <prabhakar.pkin@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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,
        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,
        Ioana Ciornei <ioana.ciornei@....com>,
        Jerin Jacob <jerinj@...vell.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Jiri Pirko <jiri@...dia.com>,
        Linu Cherian <lcherian@...vell.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-omap@...r.kernel.org, linux-staging@...ts.linux.dev,
        Manish Chopra <manishc@...vell.com>,
        Michael Chan <michael.chan@...adcom.com>,
        netdev@...r.kernel.org, oss-drivers@...igine.com,
        Richard Cochran <richardcochran@...il.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        Satanand Burla <sburla@...vell.com>,
        Shannon Nelson <snelson@...sando.io>,
        Simon Horman <simon.horman@...igine.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        Sunil Goutham <sgoutham@...vell.com>,
        Taras Chornyi <tchornyi@...vell.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        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>,
        Prabhakar Kushwaha <pkushwaha@...vell.com>,
        Shai Malin <malin1024@...il.com>,
        Shai Malin <smalin@...vell.com>, rtoshniwal@...vell.com,
        Omkar Kulkarni <okulkarni@...vell.com>
Subject: Re: [PATCH net-next] devlink: Set device as early as possible

On Tue, Aug 10, 2021 at 06:08:51PM +0530, Prabhakar Kushwaha wrote:
> Hi Leon,

<...>

> >  struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
> > -                                size_t priv_size, struct net *net)
> > +                                size_t priv_size, struct net *net,
> > +                                struct device *dev)
> >  {
> >         struct devlink *devlink;
> >
> > -       if (WARN_ON(!ops))
> > -               return NULL;
> > -
> > +       WARN_ON(!ops || !dev);
> >         if (!devlink_reload_actions_valid(ops))
> >                 return NULL;
> >
> >         devlink = kzalloc(sizeof(*devlink) + priv_size, GFP_KERNEL);
> >         if (!devlink)
> >                 return NULL;
> > +
> > +       devlink->dev = dev;
> >         devlink->ops = ops;
> >         xa_init_flags(&devlink->snapshot_ids, XA_FLAGS_ALLOC);
> >         write_pnet(&devlink->_net, net);
> > @@ -8810,12 +8812,9 @@ EXPORT_SYMBOL_GPL(devlink_alloc_ns);
> >   *     devlink_register - Register devlink instance
> >   *
> >   *     @devlink: devlink
> > - *     @dev: parent device
> >   */
> 
> This patch is converting devlink_alloc() to devlink_alloc_register().
> 
> There are 2 APIs: devlink_alloc() and devlink_register().
> Both APIs can be used in a scenario,
>               Where devlink_alloc() can be done by code written around
> one struct dev and used by another struct dev.
> or
> This scenario is not even a valid scenario?

devlink_alloc() is used to allocated netdev structures for newly
initialized device, it is not possible to share same devlink instance
between different devices.

> 
> > -int devlink_register(struct devlink *devlink, struct device *dev)
> > +int devlink_register(struct devlink *devlink)
> >  {
> > -       WARN_ON(devlink->dev);
> > -       devlink->dev = dev;
> >         mutex_lock(&devlink_mutex);
> >         list_add_tail(&devlink->list, &devlink_list);
> >         devlink_notify(devlink, DEVLINK_CMD_NEW);
> 
> Considering device registration has been moved to devlink_alloc().
> Can the remaining code of devlink_register() be also moved in devlink_alloc()?

The line "list_add_tail(&devlink->list, &devlink_list);" makes the
devlink instance visible to the devlink netlink users. We need to be
sure that it is happening when the device is already initialized, while
devlink_alloc() is performed usually as first line in .probe() routine.

This means that we can't combine alloc an register and
devlink_alloc_register() can't be valid scenario.

Thanks

> 
> --pk