linux-kernel - Re: [PATCH 05/11] net: core: provide devm_register

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Date:   Tue, 5 May 2020 10:31:05 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Rob Herring <robh+dt@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Felix Fietkau <nbd@...nwrt.org>,
        John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Arnd Bergmann <arnd@...db.de>,
        Fabien Parent <fparent@...libre.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 05/11] net: core: provide devm_register_netdev()

On Tue,  5 May 2020 16:02:25 +0200 Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> 
> Provide devm_register_netdev() - a device resource managed variant
> of register_netdev(). This new helper will only work for net_device
> structs that have a parent device assigned and are devres managed too.
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 522288177bbd..99db537c9468 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -9519,6 +9519,54 @@ int register_netdev(struct net_device *dev)
>  }
>  EXPORT_SYMBOL(register_netdev);
>  
> +struct netdevice_devres {
> +	struct net_device *ndev;
> +};

Is there really a need to define a structure if we only need a pointer?

> +static void devm_netdev_release(struct device *dev, void *this)
> +{
> +	struct netdevice_devres *res = this;
> +
> +	unregister_netdev(res->ndev);
> +}
> +
> +/**
> + *	devm_register_netdev - resource managed variant of register_netdev()
> + *	@ndev: device to register
> + *
> + *	This is a devres variant of register_netdev() for which the unregister
> + *	function will be call automatically when the parent device of ndev
> + *	is detached.
> + */
> +int devm_register_netdev(struct net_device *ndev)
> +{
> +	struct netdevice_devres *dr;
> +	int ret;
> +
> +	/* struct net_device itself must be devres managed. */
> +	BUG_ON(!(ndev->priv_flags & IFF_IS_DEVRES));
> +	/* struct net_device must have a parent device - it will be the device
> +	 * managing this resource.
> +	 */
> +	BUG_ON(!ndev->dev.parent);

Please convert those to WARN_ON, and return an error. No need to crash
the kernel.

> +	dr = devres_alloc(devm_netdev_release, sizeof(*dr), GFP_KERNEL);
> +	if (!dr)
> +		return -ENOMEM;
> +
> +	ret = register_netdev(ndev);
> +	if (ret) {
> +		devres_free(dr);
> +		return ret;
> +	}
> +
> +	dr->ndev = ndev;
> +	devres_add(ndev->dev.parent, dr);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(devm_register_netdev);