netdev - Re: [PATCH v2 1/2] ipv6: save route expiry in RTA_EXPIRES if RTF

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Date:   Fri, 19 Aug 2016 13:26:16 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Andrew Yourtchenko <ayourtch@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH v2 1/2] ipv6: save route expiry in RTA_EXPIRES if
 RTF_EXPIRES set

On Fri, 2016-08-19 at 18:41 +0200, Andrew Yourtchenko wrote:
> This allows "ip -6 route save" to save the expiry for the routes
> that have it, such that it can be correctly restored later by
> "ip -6 route restore".
> 
> If a route has RTF_EXPIRES set, generate RTA_EXPIRES value which
> will be used to restore the flag and expiry value by already
> existing code in rtm_to_fib6_config.
> 
> The expiry was already being saved as part of RTA_CACHEINFO
> in rtnl_put_cacheinfo(), but adding code to generate RTF_EXPIRES upon save
> looked more appropriate than redundant cherrypicking from
> RTA_CACHEINFO upon restore.
> 
> Signed-off-by: Andrew Yourtchenko <ayourtch@...il.com>
> ---
> Changes since v1 [1]: 
>  * fixed the indentation in a multiline function call
>    as per David Miller's review
> 
> [1] v1: http://marc.info/?l=linux-netdev&m=147135597422280&w=2
> 
>  net/ipv6/route.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4981755..f5b987d 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -3244,6 +3244,14 @@ static int rt6_fill_node(struct net *net,
>  	if (rtnl_put_cacheinfo(skb, &rt->dst, 0, expires, rt->dst.error) < 0)
>  		goto nla_put_failure;
>  
> +	/* Can't rely on expires == 0. It is zero if no expires flag,
> +	 * or if the timing is precisely at expiry. So, recheck the flag.
> +	 */
> +	if (rt->rt6i_flags & RTF_EXPIRES)
> +		if (nla_put_u32(skb, RTA_EXPIRES,
> +				expires > 0 ? expires / HZ : 0))
> +			goto nla_put_failure;
> +

Why sending (kernel -> user) the value in second units, while the other
direction (user -> kernel) expects hz ?

iproute2$ git grep -n RTA_EXPIRES
include/linux/rtnetlink.h:389:  RTA_EXPIRES,
ip/iproute.c:930:                       addattr32(&req.n, sizeof(req), RTA_EXPIRES, expires*hz);

kernel patch : (32bc201e1974976b7d3fea9a9b17bb7392ca6394)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -2809,6 +2810,15 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
        if (tb[RTA_ENCAP_TYPE])
                cfg->fc_encap_type = nla_get_u16(tb[RTA_ENCAP_TYPE]);
 
+       if (tb[RTA_EXPIRES]) {
+               unsigned long timeout = addrconf_timeout_fixup(nla_get_u32(tb[RTA_EXPIRES]), HZ);
+
+               if (addrconf_finite_timeout(timeout)) {
+                       cfg->fc_expires = jiffies_to_clock_t(timeout * HZ);
+                       cfg->fc_flags |= RTF_EXPIRES;
+               }
+       }
+