Subject: Re: [PATCH 5/7] CAN: Add virtual CAN netdevice driver

From: Arnaldo Carvalho de Melo <[email-masked]>
Date: Tue, 2 Oct 2007 11:20:16 -0300

Em Tue, Oct 02, 2007 at 03:10:11PM +0200, Urs Thuermann escreveu:
> This patch adds the virtual CAN bus (vcan) network driver.
> The vcan device is just a loopback device for CAN frames, no
> real CAN hardware is involved.
> 
> Signed-off-by: Oliver Hartkopp <[email-masked]>
> Signed-off-by: Urs Thuermann <[email-masked]>
> 
> ---
>  drivers/net/Makefile     |    1 
>  drivers/net/can/Kconfig  |   25 +++++
>  drivers/net/can/Makefile |    5 +
>  drivers/net/can/vcan.c   |  207 +++++++++++++++++++++++++++++++++++++++++++++++
>  net/can/Kconfig          |    3 
>  5 files changed, 241 insertions(+)
> 
> Index: net-2.6.24/drivers/net/Makefile
> ===================================================================
> --- net-2.6.24.orig/drivers/net/Makefile	2007-09-20 23:46:01.000000000 +0200
> +++ net-2.6.24/drivers/net/Makefile	2007-10-02 12:03:30.000000000 +0200
> @@ -12,6 +12,7 @@
>  obj-$(CONFIG_CHELSIO_T1) += chelsio/
>  obj-$(CONFIG_CHELSIO_T3) += cxgb3/
>  obj-$(CONFIG_EHEA) += ehea/
> +obj-$(CONFIG_CAN) += can/
>  obj-$(CONFIG_BONDING) += bonding/
>  obj-$(CONFIG_ATL1) += atl1/
>  obj-$(CONFIG_GIANFAR) += gianfar_driver.o
> Index: net-2.6.24/drivers/net/can/Kconfig
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ net-2.6.24/drivers/net/can/Kconfig	2007-10-02 12:03:30.000000000 +0200
> @@ -0,0 +1,25 @@
> +menu "CAN Device Drivers"
> +	depends on CAN
> +
> +config CAN_VCAN
> +	tristate "Virtual Local CAN Interface (vcan)"
> + 	depends on CAN
> +	default N
> + 	---help---
> +	  Similar to the network loopback devices, vcan offers a
> +	  virtual local CAN interface.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called vcan.
> +
> +config CAN_DEBUG_DEVICES
> +	bool "CAN devices debugging messages"
> +	depends on CAN
> +	default N
> +	---help---
> +	  Say Y here if you want the CAN device drivers to produce a bunch of
> +	  debug messages to the system log.  Select this if you are having
> +	  a problem with CAN support and want to see more of what is going
> +	  on.
> +
> +endmenu
> Index: net-2.6.24/drivers/net/can/Makefile
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ net-2.6.24/drivers/net/can/Makefile	2007-10-02 12:03:30.000000000 +0200
> @@ -0,0 +1,5 @@
> +#
> +#  Makefile for the Linux Controller Area Network drivers.
> +#
> +
> +obj-$(CONFIG_CAN_VCAN)		+= vcan.o
> Index: net-2.6.24/drivers/net/can/vcan.c
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ net-2.6.24/drivers/net/can/vcan.c	2007-10-02 12:03:30.000000000 +0200
> @@ -0,0 +1,207 @@
> +/*
> + * vcan.c - Virtual CAN interface
> + *
> + * Copyright (c) 2002-2007 Volkswagen Group Electronic Research
> + * All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + * 1. Redistributions of source code must retain the above copyright
> + *    notice, this list of conditions and the following disclaimer.
> + * 2. Redistributions in binary form must reproduce the above copyright
> + *    notice, this list of conditions and the following disclaimer in the
> + *    documentation and/or other materials provided with the distribution.
> + * 3. Neither the name of Volkswagen nor the names of its contributors
> + *    may be used to endorse or promote products derived from this software
> + *    without specific prior written permission.
> + *
> + * Alternatively, provided that this notice is retained in full, this
> + * software may be distributed under the terms of the GNU General
> + * Public License ("GPL") version 2, in which case the provisions of the
> + * GPL apply INSTEAD OF those given above.
> + *
> + * The provided data structures and external interfaces from this code
> + * are not restricted to be used by modules with a GPL compatible license.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
> + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
> + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
> + * DAMAGE.
> + *
> + * Send feedback to <[email-masked]>
> + *
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/netdevice.h>
> +#include <linux/if_arp.h>
> +#include <linux/if_ether.h>
> +#include <linux/can.h>
> +#include <net/rtnetlink.h>
> +
> +static __initdata const char banner[] =
> +	KERN_INFO "vcan: Virtual CAN interface driver\n";
> +
> +MODULE_DESCRIPTION("virtual CAN interface");
> +MODULE_LICENSE("Dual BSD/GPL");
> +MODULE_AUTHOR("Urs Thuermann <[email-masked]>");
> +
> +#ifdef CONFIG_CAN_DEBUG_DEVICES
> +static int debug;
> +module_param(debug, int, S_IRUGO);
> +#endif

Can debug be a boolean? Like its counterpart on DCCP:

net/dccp/proto.c:

module_param(dccp_debug, bool, 0444);

Where we also use a namespace prefix, for those of us who use ctags or
cscope.

> +
> +/* To be moved to linux/can/dev.h */

Is this comment still valid? If so can this move happen now? If not I
think it would be better to stick a "FIXME: " just before it, no?

> +#ifdef CONFIG_CAN_DEBUG_DEVICES
> +#define DBG(fmt, args...)  (debug & 1 ? \
> +				printk(KERN_DEBUG "vcan %s: " fmt, \
> +				__func__, ##args) : 0)
> +#else
> +#define DBG(fmt, args...)
> +#endif
> +
> +
> +/*
> + * CAN test feature:
> + * Enable the echo on driver level for testing the CAN core echo modes.
> + * See Documentation/networking/can.txt for details.
> + */
> +
> +static int echo; /* echo testing. Default: 0 (Off) */
> +module_param(echo, int, S_IRUGO);
> +MODULE_PARM_DESC(echo, "Echo sent frames (for testing). Default: 0 (Off)");

echo also seems to be a boolean

> +
> +
> +static int vcan_open(struct net_device *dev)
> +{
> +	DBG("%s: interface up\n", dev->name);
> +
> +	netif_start_queue(dev);
> +	return 0;
> +}
> +
> +static int vcan_stop(struct net_device *dev)
> +{
> +	DBG("%s: interface down\n", dev->name);
> +
> +	netif_stop_queue(dev);
> +	return 0;
> +}

Thinking out loud: I guess these days we can try to reduce the clutter
on the source code for things like "hey, I entered function foo" using
simple systemtap scripts, that could even be shipped with the kernel
sources. Not something pressing right now, just a suggestion.

> +static void vcan_rx(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct net_device_stats *stats = &dev->stats;
> +
> +	stats->rx_packets++;
> +	stats->rx_bytes += skb->len;
> +
> +	skb->protocol  = htons(ETH_P_CAN);
> +	skb->pkt_type  = PACKET_BROADCAST;
> +	skb->dev       = dev;
> +	skb->ip_summed = CHECKSUM_UNNECESSARY;
> +
> +	DBG("received skbuff on interface %d\n", dev->ifindex);
> +
> +	netif_rx(skb);
> +}
> +
> +static int vcan_tx(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct net_device_stats *stats = &dev->stats;
> +	int loop;
> +
> +	DBG("sending skbuff on interface %s\n", dev->name);
> +
> +	stats->tx_packets++;
> +	stats->tx_bytes += skb->len;
> +
> +	/* set flag whether this packet has to be looped back */
> +	loop = skb->pkt_type == PACKET_LOOPBACK;
> +
> +	if (!echo) {
> +		/* no echo handling available inside this driver */
> +
> +		if (loop) {
> +			/*
> +			 * only count the packets here, because the
> +			 * CAN core already did the echo for us
> +			 */
> +			stats->rx_packets++;
> +			stats->rx_bytes += skb->len;
> +		}
> +		kfree_skb(skb);
> +		return 0;
> +	}
> +
> +	/* perform standard echo handling for CAN network interfaces */
> +
> +	if (loop) {
> +		struct sock *srcsk = skb->sk;
> +
> +		skb = skb_share_check(skb, GFP_ATOMIC);
> +		if (!skb)
> +			return 0;
> +
> +		/* receive with packet counting */
> +		skb->sk = srcsk;
> +		vcan_rx(skb, dev);
> +	} else {
> +		/* no looped packets => no counting */
> +		kfree_skb(skb);
> +	}
> +	return 0;
> +}
> +
> +static void vcan_setup(struct net_device *dev)
> +{
> +	DBG("dev %s\n", dev->name);
> +
> +	dev->type              = ARPHRD_CAN;
> +	dev->mtu               = sizeof(struct can_frame);
> +	dev->hard_header_len   = 0;
> +	dev->addr_len          = 0;
> +	dev->tx_queue_len      = 0;
> +	dev->flags             = IFF_NOARP;
> +
> +	/* set flags according to driver capabilities */
> +	if (echo)
> +		dev->flags |= IFF_ECHO;
> +
> +	dev->open              = vcan_open;
> +	dev->stop              = vcan_stop;
> +	dev->hard_start_xmit   = vcan_tx;
> +	dev->destructor        = free_netdev;
> +}
> +
> +static struct rtnl_link_ops vcan_link_ops __read_mostly = {
> +       .kind           = "vcan",
> +       .setup          = vcan_setup,
> +};
> +
> +static __init int vcan_init_module(void)
> +{
> +	printk(banner);
> +
> +	if (echo)
> +		printk(KERN_INFO "vcan: enabled echo on driver level.\n");
> +
> +	return rtnl_link_register(&vcan_link_ops);
> +}
> +
> +static __exit void vcan_cleanup_module(void)
> +{
> +	rtnl_link_unregister(&vcan_link_ops);
> +}
> +
> +module_init(vcan_init_module);
> +module_exit(vcan_cleanup_module);
> Index: net-2.6.24/net/can/Kconfig
> ===================================================================
> --- net-2.6.24.orig/net/can/Kconfig	2007-10-02 12:03:28.000000000 +0200
> +++ net-2.6.24/net/can/Kconfig	2007-10-02 12:03:30.000000000 +0200
> @@ -47,3 +47,6 @@
>  	  Say Y here if you want the CAN core to produce a bunch of debug
>  	  messages to the system log.  Select this if you are having a
>  	  problem with CAN support and want to see more of what is going on.
> +
> +
> +source "drivers/net/can/Kconfig"
> 
> --