Subject: Re: [PATCH] IPv6: Add 'autoconf' and 'disable_ipv6' module parameters

From: Vlad Yasevich <[email-masked]>
Date: Tue, 24 Mar 2009 22:12:37 -0400

Brian Haley wrote:
> This is the quick and easy patch to add autoconf and
> disable_ipv6 module parameters to IPv6.  I don't think anything
> more complicated is needed, assuming you play with the /etc
> configuration files.
> 
> For example, if you wanted to enable IPv6 just on 'lo' you
> would:
> 
> 1. Add "ipv6" to /etc/modules (if you don't, step #3 might fail)
> 
> 2. Add this to /etc/modprobe.conf:
> 
> 	options ipv6 disable_ipv6=1
> 
> 3. Add these to /etc/sysctl.conf:
> 
> 	net.ipv6.conf.all.disable_ipv6=0
> 	net.ipv6.conf.lo.disable_ipv6=0

This is kind of confusing.  First you say, disable IPv6, then you say enable IPv6, but
nothing happens.  Unless you typo-ed the 'all.disable_ipv6 = 0'...

Also, it looks like if someone decides to switch IPv6 back on for a particular
interface, they would have to wait until the next RA to get an address.  Not an
optimum solution.

> 
> # ip -6 a
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 
>     inet6 ::1/128 scope host 
>        valid_lft forever preferred_lft forever
> 
> The wording can probably be cleaned-up a little in ipv6.txt,
> comments welcome.
> 
> 
> ---------------------------------------------------------------
> 
> Add 'autoconf' and 'disable_ipv6' parameters to the IPv6 module.
> 
> The first controls if IPv6 addresses are autoconfigured from
> prefixes received in Router Advertisements.  The IPv6 loopback
> (::1) and link-local addresses are still configured.
> 
> The second controls if IPv6 addresses are desired at all.  No
> IPv6 addresses will be added to any interfaces.
> 
> Signed-off-by: Brian Haley <[email-masked]>
> ---
>  Documentation/networking/ipv6.txt |   37 +++++++++++++++++++++++++++++++++++++
>  include/linux/ipv6.h              |    6 ++++++
>  net/ipv6/addrconf.c               |   12 +++++++++---
>  net/ipv6/af_inet6.c               |   22 +++++++++++++++++-----
>  4 files changed, 69 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/networking/ipv6.txt b/Documentation/networking/ipv6.txt
> index 268e5c1..9fd7e21 100644
> --- a/Documentation/networking/ipv6.txt
> +++ b/Documentation/networking/ipv6.txt
> @@ -33,3 +33,40 @@ disable
>  
>  		A reboot is required to enable IPv6.
>  
> +autoconf
> +
> +	Specifies whether to enable IPv6 address autoconfiguration
> +	on all interfaces.  This might be used when one does not wish
> +	for addresses to be automatically generated from prefixes
> +	received in Router Advertisements.
> +
> +	The possible values and their effects are:
> +
> +	0
> +		IPv6 address autoconfiguration is disabled on all interfaces.
> +
> +		Only the IPv6 loopback address (::1) and link-local addresses
> +		will be added to interfaces.
> +
> +	1
> +		IPv6 address autoconfiguration is enabled on all interfaces.
> +
> +		This is the default value.
> +
> +disable_ipv6
> +
> +	Specifies whether to disable IPv6 on all interfaces.
> +	This might be used when no IPv6 addresses are desired.
> +
> +	The possible values and their effects are:
> +
> +	0
> +		IPv6 is enabled on all interfaces.
> +
> +		This is the default value.
> +
> +	1
> +		IPv6 is disabled on all interfaces.
> +
> +		No IPv6 addresses will be added to interfaces.
> +
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index 476d946..c662efa 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -169,6 +169,12 @@ struct ipv6_devconf {
>  	__s32		accept_dad;
>  	void		*sysctl;
>  };
> +
> +struct ipv6_params {
> +	__s32 disable_ipv6;
> +	__s32 autoconf;
> +};
> +extern struct ipv6_params ipv6_defaults;
>  #endif
>  
>  /* index values for the variables in ipv6_devconf */
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 8499da9..da6f01e 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1784,6 +1784,7 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len)
>  	__u32 prefered_lft;
>  	int addr_type;
>  	struct inet6_dev *in6_dev;
> +	struct net *net = dev_net(dev);
>  
>  	pinfo = (struct prefix_info *) opt;
>  
> @@ -1841,7 +1842,7 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len)
>  		if (addrconf_finite_timeout(rt_expires))
>  			rt_expires *= HZ;
>  
> -		rt = rt6_lookup(dev_net(dev), &pinfo->prefix, NULL,
> +		rt = rt6_lookup(net, &pinfo->prefix, NULL,
>  				dev->ifindex, 1);
>  
>  		if (rt && addrconf_is_prefix_route(rt)) {
> @@ -1874,11 +1875,11 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len)
>  
>  	/* Try to figure out our local address for this prefix */
>  
> -	if (pinfo->autoconf && in6_dev->cnf.autoconf) {
> +	if (pinfo->autoconf && in6_dev->cnf.autoconf &&
> +	    net->ipv6.devconf_all->autoconf) {
>  		struct inet6_ifaddr * ifp;
>  		struct in6_addr addr;
>  		int create = 0, update_lft = 0;
> -		struct net *net = dev_net(dev);
>  
>  		if (pinfo->prefix_len == 64) {
>  			memcpy(&addr, &pinfo->prefix, 8);
> @@ -4378,6 +4379,11 @@ static int addrconf_init_net(struct net *net)
>  		dflt = kmemdup(dflt, sizeof(ipv6_devconf_dflt), GFP_KERNEL);
>  		if (dflt == NULL)
>  			goto err_alloc_dflt;
> +	} else {
> +		/* these will be inherited by all namespaces */
> +		all->autoconf = dflt->autoconf = ipv6_defaults.autoconf;
> +		all->disable_ipv6 = dflt->disable_ipv6 =
> +			ipv6_defaults.disable_ipv6;

Why set 'all'?  Since no interfaces are created yet, setting dflt accomplishes
what you want.

-vlad

>  	}
>  
>  	net->ipv6.devconf_all = all;
> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index fbf533c..7278dce 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -72,9 +72,21 @@ MODULE_LICENSE("GPL");
>  static struct list_head inetsw6[SOCK_MAX];
>  static DEFINE_SPINLOCK(inetsw6_lock);
>  
> -static int disable_ipv6 = 0;
> -module_param_named(disable, disable_ipv6, int, 0);
> -MODULE_PARM_DESC(disable, "Disable IPv6 such that it is non-functional");
> +struct ipv6_params ipv6_defaults = {
> +	.disable_ipv6 = 0,
> +	.autoconf = 1,
> +};
> +
> +static int disable_ipv6_mod = 0;
> +
> +module_param_named(disable, disable_ipv6_mod, int, 0444);
> +MODULE_PARM_DESC(disable, "Disable IPv6 module such that it is non-functional");
> +
> +module_param_named(disable_ipv6, ipv6_defaults.disable_ipv6, int, 0444);
> +MODULE_PARM_DESC(disable_ipv6, "Disable IPv6 on all interfaces");
> +
> +module_param_named(autoconf, ipv6_defaults.autoconf, int, 0444);
> +MODULE_PARM_DESC(autoconf, "Enable IPv6 address autoconfiguration on all interfaces");
>  
>  static __inline__ struct ipv6_pinfo *inet6_sk_generic(struct sock *sk)
>  {
> @@ -1013,7 +1025,7 @@ static int __init inet6_init(void)
>  	for(r = &inetsw6[0]; r < &inetsw6[SOCK_MAX]; ++r)
>  		INIT_LIST_HEAD(r);
>  
> -	if (disable_ipv6) {
> +	if (disable_ipv6_mod) {
>  		printk(KERN_INFO
>  		       "IPv6: Loaded, but administratively disabled, "
>  		       "reboot required to enable\n");
> @@ -1202,7 +1214,7 @@ module_init(inet6_init);
>  
>  static void __exit inet6_exit(void)
>  {
> -	if (disable_ipv6)
> +	if (disable_ipv6_mod)
>  		return;
>  
>  	/* First of all disallow new sockets creation. */