Subject: Re: [patch net-next v2 5/9] net: introduce dummy switch

From: Florian Fainelli <[email-masked]>
Date: Fri, 19 Sep 2014 22:21:00 -0700

On 09/19/14 06:49, Jiri Pirko wrote:
> Dummy switch implementation using switchdev interface

This really looks like a DSA driver that has 0 ports, and is not 
attached to an useful network interface, and which is registering its 
own set of rtnl operations for a purpose that is unclear to me.

I think registering these rtnl ops is misleading as it leads to a false 
idea that this is allowed, and that people are actually encouraged to do 
that for custom switch drivers, and this completely defeats the purpose 
of coming up with a generic API.

If we are to go that route anyway, I really prefer the way Felix did it 
in swconfig, and the fake switch driver did do something useful being 
attached to the loopback interface:

http://lists.openwall.net/netdev/2013/10/22/103
http://patchwork.ozlabs.org/patch/285478/

>
> Signed-off-by: Jiri Pirko <[email-masked]>
> ---
>   drivers/net/Kconfig          |   7 +++
>   drivers/net/Makefile         |   1 +
>   drivers/net/dummyswitch.c    | 130 +++++++++++++++++++++++++++++++++++++++++++
>   include/uapi/linux/if_link.h |   9 +++
>   4 files changed, 147 insertions(+)
>   create mode 100644 drivers/net/dummyswitch.c
>
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index c6f6f69..7822c74 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -71,6 +71,13 @@ config DUMMY
>   	  To compile this driver as a module, choose M here: the module
>   	  will be called dummy.
>
> +config NET_DUMMY_SWITCH
> +	tristate "Dummy switch net driver support"
> +	depends on NET_SWITCHDEV
> +	---help---
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called dummyswitch.
> +
>   config EQUALIZER
>   	tristate "EQL (serial line load balancing) support"
>   	---help---
> diff --git a/drivers/net/Makefile b/drivers/net/Makefile
> index 61aefdd..3c835ba 100644
> --- a/drivers/net/Makefile
> +++ b/drivers/net/Makefile
> @@ -7,6 +7,7 @@
>   #
>   obj-$(CONFIG_BONDING) += bonding/
>   obj-$(CONFIG_DUMMY) += dummy.o
> +obj-$(CONFIG_NET_DUMMY_SWITCH) += dummyswitch.o
>   obj-$(CONFIG_EQUALIZER) += eql.o
>   obj-$(CONFIG_IFB) += ifb.o
>   obj-$(CONFIG_MACVLAN) += macvlan.o
> diff --git a/drivers/net/dummyswitch.c b/drivers/net/dummyswitch.c
> new file mode 100644
> index 0000000..e7a48f4
> --- /dev/null
> +++ b/drivers/net/dummyswitch.c
> @@ -0,0 +1,130 @@
> +/*
> + * drivers/net/dummyswitch.c - Dummy switch device
> + * Copyright (c) 2014 Jiri Pirko <[email-masked]>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/netdevice.h>
> +#include <linux/etherdevice.h>
> +#include <net/rtnetlink.h>
> +
> +struct dummyswport_priv {
> +	struct netdev_phys_item_id psid;
> +};
> +
> +static netdev_tx_t dummyswport_start_xmit(struct sk_buff *skb,
> +					  struct net_device *dev)
> +{
> +	dev_kfree_skb(skb);
> +	return NETDEV_TX_OK;
> +}
> +
> +static int dummyswport_swdev_id_get(struct net_device *dev,
> +				    struct netdev_phys_item_id *psid)
> +{
> +	struct dummyswport_priv *dsp = netdev_priv(dev);
> +
> +	memcpy(psid, &dsp->psid, sizeof(*psid));
> +	return 0;
> +}
> +
> +static int dummyswport_change_carrier(struct net_device *dev, bool new_carrier)
> +{
> +	if (new_carrier)
> +		netif_carrier_on(dev);
> +	else
> +		netif_carrier_off(dev);
> +	return 0;
> +}
> +
> +static const struct net_device_ops dummyswport_netdev_ops = {
> +	.ndo_start_xmit		= dummyswport_start_xmit,
> +	.ndo_swdev_id_get	= dummyswport_swdev_id_get,
> +	.ndo_change_carrier	= dummyswport_change_carrier,
> +};
> +
> +static void dummyswport_setup(struct net_device *dev)
> +{
> +	ether_setup(dev);
> +
> +	/* Initialize the device structure. */
> +	dev->netdev_ops = &dummyswport_netdev_ops;
> +	dev->destructor = free_netdev;
> +
> +	/* Fill in device structure with ethernet-generic values. */
> +	dev->tx_queue_len = 0;
> +	dev->flags |= IFF_NOARP;
> +	dev->flags &= ~IFF_MULTICAST;
> +	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
> +	dev->features	|= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
> +	dev->features	|= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
> +	eth_hw_addr_random(dev);
> +}
> +
> +static int dummyswport_validate(struct nlattr *tb[], struct nlattr *data[])
> +{
> +	if (tb[IFLA_ADDRESS])
> +		return -EINVAL;
> +	if (!data || !data[IFLA_DUMMYSWPORT_PHYS_SWITCH_ID])
> +		return -EINVAL;
> +	return 0;
> +}
> +
> +static int dummyswport_newlink(struct net *src_net, struct net_device *dev,
> +			       struct nlattr *tb[], struct nlattr *data[])
> +{
> +	struct dummyswport_priv *dsp = netdev_priv(dev);
> +	int err;
> +
> +	dsp->psid.id_len = nla_len(data[IFLA_DUMMYSWPORT_PHYS_SWITCH_ID]);
> +	memcpy(dsp->psid.id, nla_data(data[IFLA_DUMMYSWPORT_PHYS_SWITCH_ID]),
> +	       dsp->psid.id_len);
> +
> +	err = register_netdevice(dev);
> +	if (err)
> +		return err;
> +
> +	netif_carrier_on(dev);
> +
> +	return 0;
> +}
> +
> +static const struct nla_policy dummyswport_policy[IFLA_DUMMYSWPORT_MAX + 1] = {
> +	[IFLA_DUMMYSWPORT_PHYS_SWITCH_ID] = { .type = NLA_BINARY,
> +					      .len = MAX_PHYS_ITEM_ID_LEN },
> +};
> +
> +static struct rtnl_link_ops dummyswport_link_ops __read_mostly = {
> +	.kind		= "dummyswport",
> +	.priv_size	= sizeof(struct dummyswport_priv),
> +	.setup		= dummyswport_setup,
> +	.validate	= dummyswport_validate,
> +	.newlink	= dummyswport_newlink,
> +	.policy		= dummyswport_policy,
> +	.maxtype	= IFLA_DUMMYSWPORT_MAX,
> +};
> +
> +static int __init dummysw_module_init(void)
> +{
> +	return rtnl_link_register(&dummyswport_link_ops);
> +}
> +
> +static void __exit dummysw_module_exit(void)
> +{
> +	rtnl_link_unregister(&dummyswport_link_ops);
> +}
> +
> +module_init(dummysw_module_init);
> +module_exit(dummysw_module_exit);
> +
> +MODULE_LICENSE("GPL v2");
> +MODULE_AUTHOR("Jiri Pirko <[email-masked]>");
> +MODULE_DESCRIPTION("Dummy switch device");
> +MODULE_ALIAS_RTNL_LINK("dummyswport");
> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
> index c5ca3b9..bd24d69 100644
> --- a/include/uapi/linux/if_link.h
> +++ b/include/uapi/linux/if_link.h
> @@ -574,4 +574,13 @@ enum {
>
>   #define IFLA_HSR_MAX (__IFLA_HSR_MAX - 1)
>
> +/* DUMMYSWPORT section */
> +enum {
> +	IFLA_DUMMYSWPORT_UNSPEC,
> +	IFLA_DUMMYSWPORT_PHYS_SWITCH_ID,
> +	__IFLA_DUMMYSWPORT_MAX,
> +};
> +
> +#define IFLA_DUMMYSWPORT_MAX (__IFLA_DUMMYSWPORT_MAX - 1)
> +
>   #endif /* _UAPI_LINUX_IF_LINK_H */
>