netdev - Re: [PATCH net-next 3/5] devlink: create a special NDO for getting the devlink instance

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Date:   Fri, 22 Feb 2019 10:51:31 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     davem@...emloft.net, jiri@...nulli.us, andrew@...n.ch,
        f.fainelli@...il.com, netdev@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [PATCH net-next 3/5] devlink: create a special NDO for getting
 the devlink instance

On Thu, Feb 21, 2019 at 09:46:18AM -0800, Jakub Kicinski wrote:
> Instead of iterating over all devlink ports add a NDO which
> will return the devlink instance from the driver.
> 
> Suggested-by: Jiri Pirko <jiri@...nulli.us>
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> ---
>  include/linux/netdevice.h |  6 ++++
>  net/core/devlink.c        | 62 +++++++++++++--------------------------
>  2 files changed, 26 insertions(+), 42 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index aab4d9f6613d..eebcef6b8191 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -940,6 +940,8 @@ struct dev_ifalias {
>  	char ifalias[];
>  };
>  
> +struct devlink;
> +
>  /*
>   * This structure defines the management hooks for network devices.
>   * The following hooks can be defined; unless noted otherwise, they are
> @@ -1248,6 +1250,9 @@ struct dev_ifalias {
>   *	that got dropped are freed/returned via xdp_return_frame().
>   *	Returns negative number, means general error invoking ndo, meaning
>   *	no frames were xmit'ed and core-caller will free all frames.
> + * struct devlink *(*ndo_get_devlink)(struct net_device *dev);
> + *	Get devlink instance associated with a given netdev.
> + *	Called with a reference on the device only, rtnl_lock is not held.

The formulation is a bit ambiguous. Do I understand correctly that what
it says is that device reference is sufficient and rtnl_lock is not
necessary (but there is no harm if caller holds rtnl_lock)?

Michal