Re: [PATCH v1 net-next 1/1] Allow user to set metric on default route learned via Router Advertisement.

From: David Ahern
Date: Thu Jan 14 2021 - 21:28:29 EST

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In reply to: Praveen Chaudhary: "[PATCH v1 net-next 1/1] Allow user to set metric on default route learned via Router Advertisement."
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On 1/12/21 6:50 PM, Praveen Chaudhary wrote:
> For IPv4, default route is learned via DHCPv4 and user is allowed to change
> metric using config etc/network/interfaces. But for IPv6, default route can
> be learned via RA, for which, currently a fixed metric value 1024 is used.
>
> Ideally, user should be able to configure metric on default route for IPv6
> similar to IPv4. This fix adds sysctl for the same.

This is a single patch set, so the details you have in the cover letter
should be in this description here. Also, please just 'ip' commands in
the patch description; 'route' command is a dinosaur that needs to be
retired.

>
> Signed-off-by: Praveen Chaudhary<pchaudhary@xxxxxxxxxxxx>
> Signed-off-by: Zhenggen Xu<zxu@xxxxxxxxxxxx>
>
> Changes in v1.
> ---
> 1.) Correct the call to rt6_add_dflt_router.
> ---
>
> ---
> Documentation/networking/ip-sysctl.rst | 18 ++++++++++++++++++
> include/linux/ipv6.h | 1 +
> include/net/ip6_route.h | 3 ++-
> include/uapi/linux/ipv6.h | 1 +
> include/uapi/linux/sysctl.h | 1 +
> net/ipv6/addrconf.c | 10 ++++++++++
> net/ipv6/ndisc.c | 14 ++++++++++----
> net/ipv6/route.c | 5 +++--
> 8 files changed, 46 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index dd2b12a32b73..384159081d91 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -1871,6 +1871,24 @@ accept_ra_defrtr - BOOLEAN
> - enabled if accept_ra is enabled.
> - disabled if accept_ra is disabled.
>
> +accept_ra_defrtr_metric - INTEGER

Drop the 'accept' part; ra_defrtr_metric is sufficiently long. Since the
value is not from the RA, it is not really about accepting data from the RA.

> + Route metric for default route learned in Router Advertisement. This
> + value will be assigned as metric for the route learned via IPv6 Router
> + Advertisement.
> +
> + Possible values are:
> + 0:
> + Use default value i.e. IP6_RT_PRIO_USER 1024.
> + 0xFFFFFFFF to -1:
> + -ve values represent high route metric, value will be treated as
> + unsigned value. This behaviour is inline with current IPv4 metric
> + shown with commands such as "route -n" or "ip route list".
> + 1 to 0x7FFFFFF:
> + +ve values will be used as is for route metric.

route metric is a u32, so these ranges should not be needed. 'ip route
list' shows metric as a positive number only.

> +
> + Functional default: enabled if accept_ra_defrtr is enabled.
> + disabled if accept_ra_defrtr is disabled.

Alignment problem, but I think this can be moved above to the
description and changed to something like 'only takes affect if
accept_ra_defrtr' is enabled.

> +
> accept_ra_from_local - BOOLEAN
> Accept RA with source-address that is found on local machine
> if the RA is otherwise proper and able to be accepted.
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index dda61d150a13..19af90c77200 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -31,6 +31,7 @@ struct ipv6_devconf {
> __s32 max_desync_factor;
> __s32 max_addresses;
> __s32 accept_ra_defrtr;
> + __s32 accept_ra_defrtr_metric;

__u32 and drop the 'accept_' prefix.

> __s32 accept_ra_min_hop_limit;
> __s32 accept_ra_pinfo;
> __s32 ignore_routes_with_linkdown;
> diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
> index 2a5277758379..a470bdab2420 100644
> --- a/include/net/ip6_route.h
> +++ b/include/net/ip6_route.h
> @@ -174,7 +174,8 @@ struct fib6_info *rt6_get_dflt_router(struct net *net,
> struct net_device *dev);
> struct fib6_info *rt6_add_dflt_router(struct net *net,
> const struct in6_addr *gwaddr,
> - struct net_device *dev, unsigned int pref);
> + struct net_device *dev, unsigned int pref,
> + unsigned int defrtr_usr_metric);

u32 for consistency

>
> void rt6_purge_dflt_routers(struct net *net);
>
> diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
> index 13e8751bf24a..945de5de5144 100644
> --- a/include/uapi/linux/ipv6.h
> +++ b/include/uapi/linux/ipv6.h
> @@ -189,6 +189,7 @@ enum {
> DEVCONF_ACCEPT_RA_RT_INFO_MIN_PLEN,
> DEVCONF_NDISC_TCLASS,
> DEVCONF_RPL_SEG_ENABLED,
> + DEVCONF_ACCEPT_RA_DEFRTR_METRIC,

Drop 'ACCEPT_'

> DEVCONF_MAX
> };
>
> diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
> index 458179df9b27..5e79c196e33c 100644
> --- a/include/uapi/linux/sysctl.h
> +++ b/include/uapi/linux/sysctl.h
> @@ -571,6 +571,7 @@ enum {
> NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> NET_IPV6_ACCEPT_RA_FROM_LOCAL=26,
> NET_IPV6_ACCEPT_RA_RT_INFO_MIN_PLEN=27,
> + NET_IPV6_ACCEPT_RA_DEFRTR_METRIC=28,

Drop 'ACCEPT_'

> __NET_IPV6_MAX
> };
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index eff2cacd5209..702ec4a33936 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -205,6 +205,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
> .max_desync_factor = MAX_DESYNC_FACTOR,
> .max_addresses = IPV6_MAX_ADDRESSES,
> .accept_ra_defrtr = 1,
> + .accept_ra_defrtr_metric = 0,
> .accept_ra_from_local = 0,
> .accept_ra_min_hop_limit= 1,
> .accept_ra_pinfo = 1,
> @@ -260,6 +261,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
> .max_desync_factor = MAX_DESYNC_FACTOR,
> .max_addresses = IPV6_MAX_ADDRESSES,
> .accept_ra_defrtr = 1,
> + .accept_ra_defrtr_metric = 0,
> .accept_ra_from_local = 0,
> .accept_ra_min_hop_limit= 1,
> .accept_ra_pinfo = 1,
> @@ -5475,6 +5477,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
> array[DEVCONF_MAX_DESYNC_FACTOR] = cnf->max_desync_factor;
> array[DEVCONF_MAX_ADDRESSES] = cnf->max_addresses;
> array[DEVCONF_ACCEPT_RA_DEFRTR] = cnf->accept_ra_defrtr;
> + array[DEVCONF_ACCEPT_RA_DEFRTR_METRIC] = cnf->accept_ra_defrtr_metric;
> array[DEVCONF_ACCEPT_RA_MIN_HOP_LIMIT] = cnf->accept_ra_min_hop_limit;
> array[DEVCONF_ACCEPT_RA_PINFO] = cnf->accept_ra_pinfo;
> #ifdef CONFIG_IPV6_ROUTER_PREF
> @@ -6667,6 +6670,13 @@ static const struct ctl_table addrconf_sysctl[] = {
> .mode = 0644,
> .proc_handler = proc_dointvec,
> },
> + {
> + .procname = "accept_ra_defrtr_metric",
> + .data = &ipv6_devconf.accept_ra_defrtr_metric,
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = proc_dointvec,

proc_douintvec

> + },
> {
> .procname = "accept_ra_min_hop_limit",
> .data = &ipv6_devconf.accept_ra_min_hop_limit,
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index 76717478f173..96ab202e95f9 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -1180,6 +1180,7 @@ static void ndisc_router_discovery(struct sk_buff *skb)
> unsigned int pref = 0;
> __u32 old_if_flags;
> bool send_ifinfo_notify = false;
> + unsigned int defrtr_usr_metric = 0;

net coding style is reverse xmas tree - ie., longest to shortest. yes,
this function is old school, but new entries can be added in the right
place. Since you set before use, the initialization to 0 is not
necessary. And u32 for consistency.

>
> __u8 *opt = (__u8 *)(ra_msg + 1);
>
> @@ -1303,18 +1304,23 @@ static void ndisc_router_discovery(struct sk_buff *skb)
> return;
> }
> }
> - if (rt && lifetime == 0) {
> + /* Set default route metric if specified by user */
> + defrtr_usr_metric = in6_dev->cnf.accept_ra_defrtr_metric;
> + if (defrtr_usr_metric == 0)
> + defrtr_usr_metric = IP6_RT_PRIO_USER;
> + /* delete the route if lifetime is 0 or if metric needs change */
> + if (rt && ((lifetime == 0) || (rt->fib6_metric != defrtr_usr_metric))) {
> ip6_del_rt(net, rt, false);
> rt = NULL;
> }
>
> - ND_PRINTK(3, info, "RA: rt: %p lifetime: %d, for dev: %s\n",
> - rt, lifetime, skb->dev->name);
> + ND_PRINTK(3, info, "RA: rt: %p lifetime: %d, metric: %d, for dev: %s\n",
> + rt, lifetime, defrtr_usr_metric, skb->dev->name);
> if (!rt && lifetime) {
> ND_PRINTK(3, info, "RA: adding default router\n");
>
> rt = rt6_add_dflt_router(net, &ipv6_hdr(skb)->saddr,
> - skb->dev, pref);
> + skb->dev, pref, defrtr_usr_metric);
> if (!rt) {
> ND_PRINTK(0, err,
> "RA: %s failed to add default route\n",
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 188e114b29b4..5f177ae97e42 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -4252,11 +4252,12 @@ struct fib6_info *rt6_get_dflt_router(struct net *net,
> struct fib6_info *rt6_add_dflt_router(struct net *net,
> const struct in6_addr *gwaddr,
> struct net_device *dev,
> - unsigned int pref)
> + unsigned int pref,
> + unsigned int defrtr_usr_metric)

u32

> {
> struct fib6_config cfg = {
> .fc_table = l3mdev_fib_table(dev) ? : RT6_TABLE_DFLT,
> - .fc_metric = IP6_RT_PRIO_USER,
> + .fc_metric = defrtr_usr_metric ? defrtr_usr_metric : IP6_RT_PRIO_USER,

you can abbreviate that as:
defrtr_usr_metric ? : IP6_RT_PRIO_USER,

> .fc_ifindex = dev->ifindex,
> .fc_flags = RTF_GATEWAY | RTF_ADDRCONF | RTF_DEFAULT |
> RTF_UP | RTF_EXPIRES | RTF_PREF(pref),
>

Next message: Philip Chen: "[PATCH v6 1/2] dt-bindings: input: cros-ec-keyb: Add a new property"
Previous message: Palmer Dabbelt: "Re: [PATCH 1/1] riscv/kasan: add KASAN_VMALLOC support"
In reply to: Praveen Chaudhary: "[PATCH v1 net-next 1/1] Allow user to set metric on default route learned via Router Advertisement."
Next in thread: Praveen Chaudhary: "RE: [PATCH v1 net-next 1/1] Allow user to set metric on default route learned via Router Advertisement."
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