Subject: Re: [PATCH 1/2] ipv6: add sysctl_mld_qrv to configure query robustness variable

From: Flavio Leitner <[email-masked]>
Date: Mon, 1 Sep 2014 21:05:54 -0300

Hi Hannes,

On Mon, Sep 01, 2014 at 09:55:34PM +0200, Hannes Frederic Sowa wrote:
> This patch adds a new sysctl_mld_qrv knob to configure the mldv1/v2 query
> robustness variable. It specifies how many retransmit of unsolicited mld
> retransmit should happen. Admins might want to tune this on lossy links.
> 
> Also reset mld state on interface down/up, so we pick up new sysctl
> settings during interface up event.
> 
> IPv6 certification requests this knob to be available.
> 
> I didn't make this knob netns specific, as it is mostly a setting in a
> physical environment and should be per host.
> 
> Cc: Flavio Leitner <[email-masked]>
> Signed-off-by: Hannes Frederic Sowa <[email-masked]>
> ---
> v2) no changes to original version
> 
>  Documentation/networking/ip-sysctl.txt |  3 +++
>  include/net/ipv6.h                     |  1 +
>  net/ipv6/mcast.c                       | 20 ++++++++++++--------
>  net/ipv6/sysctl_net_ipv6.c             | 10 ++++++++++
>  4 files changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index 3cce8ea..b7fe844 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1152,6 +1152,9 @@ anycast_src_echo_reply - BOOLEAN
>  	FALSE: disabled
>  	Default: FALSE
>  
> +mld_qrv - INTEGER
> +	Controls the MLD query robustness variable (see RFC3810 9.1).
> +
>  IPv6 Fragmentation:
>  
>  ip6frag_high_thresh - INTEGER
> diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> index a2db816..7e247e9 100644
> --- a/include/net/ipv6.h
> +++ b/include/net/ipv6.h
> @@ -121,6 +121,7 @@ struct frag_hdr {
>  
>  /* sysctls */
>  extern int sysctl_mld_max_msf;
> +extern int sysctl_mld_qrv;
>  
>  #define _DEVINC(net, statname, modifier, idev, field)			\
>  ({									\
> diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
> index 7088179..6efb0e5 100644
> --- a/net/ipv6/mcast.c
> +++ b/net/ipv6/mcast.c
> @@ -121,6 +121,7 @@ static int ip6_mc_leave_src(struct sock *sk, struct ipv6_mc_socklist *iml,
>  #define IPV6_MLD_MAX_MSF	64
>  
>  int sysctl_mld_max_msf __read_mostly = IPV6_MLD_MAX_MSF;
> +int sysctl_mld_qrv __read_mostly = MLD_QRV_DEFAULT;
>  
>  /*
>   *	socket join on multicast group
> @@ -1196,7 +1197,7 @@ static void mld_update_qrv(struct inet6_dev *idev,
>  	if (mlh2->mld2q_qrv > 0)
>  		idev->mc_qrv = mlh2->mld2q_qrv;
>  
> -	if (unlikely(idev->mc_qrv < 2)) {
> +	if (unlikely(idev->mc_qrv < MLD_QRV_DEFAULT)) {
>  		net_warn_ratelimited("IPv6: MLD: clamping QRV from %u to %u!\n",
>  				     idev->mc_qrv, MLD_QRV_DEFAULT);
>  		idev->mc_qrv = MLD_QRV_DEFAULT;

You allow the sysctl to be 1, but here it is limited to 2?

> @@ -2478,6 +2479,14 @@ void ipv6_mc_down(struct inet6_dev *idev)
>  	mld_clear_delrec(idev);
>  }
>  
> +static void ipv6_mc_reset(struct inet6_dev *idev)
> +{
> +	idev->mc_qrv = sysctl_mld_qrv;
> +	idev->mc_qi = MLD_QI_DEFAULT;
> +	idev->mc_qri = MLD_QRI_DEFAULT;
> +	idev->mc_v1_seen = 0;
> +	idev->mc_maxdelay = unsolicited_report_interval(idev);
> +}
>  
>  /* Device going up */
>  
> @@ -2488,6 +2497,7 @@ void ipv6_mc_up(struct inet6_dev *idev)
>  	/* Install multicast list, except for all-nodes (already installed) */
>  
>  	read_lock_bh(&idev->lock);
> +	ipv6_mc_reset(idev);

ok, up and down the interface to get the sysctl value applied.

>  	for (i = idev->mc_list; i; i = i->next)
>  		igmp6_group_added(i);
>  	read_unlock_bh(&idev->lock);
> @@ -2508,13 +2518,7 @@ void ipv6_mc_init_dev(struct inet6_dev *idev)
>  			(unsigned long)idev);
>  	setup_timer(&idev->mc_dad_timer, mld_dad_timer_expire,
>  		    (unsigned long)idev);
> -
> -	idev->mc_qrv = MLD_QRV_DEFAULT;
> -	idev->mc_qi = MLD_QI_DEFAULT;
> -	idev->mc_qri = MLD_QRI_DEFAULT;
> -
> -	idev->mc_maxdelay = unsolicited_report_interval(idev);
> -	idev->mc_v1_seen = 0;
> +	ipv6_mc_reset(idev);

looks good to me.

>  	write_unlock_bh(&idev->lock);
>  }
>  
> diff --git a/net/ipv6/sysctl_net_ipv6.c b/net/ipv6/sysctl_net_ipv6.c
> index 0c56c93..c5c10fa 100644
> --- a/net/ipv6/sysctl_net_ipv6.c
> +++ b/net/ipv6/sysctl_net_ipv6.c
> @@ -16,6 +16,8 @@
>  #include <net/addrconf.h>
>  #include <net/inet_frag.h>
>  
> +static int one = 1;
> +

Although that can be reused later for other purposes, it's nice to
have a comment telling where that value came from. Since you have
defined MLD_QRV_DEFAULT, it helps. Still I didn't know about 
rfc6636#section-4.5, so I'd appreciate if you include that info
either in ip-sysctl.txt or close to MLD_QRV_DEFAULT.
E.g.:

/* See RFC3810 9.1 and rfc6636 4.5 */
+int sysctl_mld_qrv __read_mostly = MLD_QRV_DEFAULT;

Actually, maybe that int could be something not specific to ipv6
because I believe there are more users of the same thing. That's ok,
just a comment and it's not part of this patch.

>  static struct ctl_table ipv6_table_template[] = {
>  	{
>  		.procname	= "bindv6only",
> @@ -63,6 +65,14 @@ static struct ctl_table ipv6_rotable[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec
>  	},
> +	{
> +		.procname	= "mld_qrv",
> +		.data		= &sysctl_mld_qrv,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &one
> +	},
>  	{ }
>  };
>  
> -- 
> 1.9.3
>