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* [PATCH 1/2 net-next] ipv4: centralize devconf sysctl handling
@ 2026-03-25 16:10 Fernando Fernandez Mancera
  2026-03-25 16:10 ` [PATCH 2/2 net-next] ipv4: ipv4: handle devconf post-set actions on netlink updates Fernando Fernandez Mancera
  0 siblings, 1 reply; 6+ messages in thread
From: Fernando Fernandez Mancera @ 2026-03-25 16:10 UTC (permalink / raw)
  To: netdev
  Cc: horms, pabeni, kuba, edumazet, dsahern, davem,
	Fernando Fernandez Mancera

The logic for handling IPv4 devconf sysctls is scattered. Notification
and cache flushes are managed in devinet_conf_proc(), while a separate
ipv4_doint_and_flush() function and DEVINET_SYSCTL_FLUSHING_ENTRY macro
is used for properties that solely require a cache flush.

This patch refactors the sysctl handling by introducing a centralized
helper, devinet_conf_post_set(). This new function evaluates the changed
attribute and handles all necessary operations like triggering netlink
notifications. It returns a boolean indicating whether a routing cache
flush is required.

Note that the boolean is necessary as this function will be re-used for
netlink IPv4 devconf handling where the cache flushing must wait until
all the attributes have been processed.

Finally, this is introducing a small change in behavior for
IPV4_DEVCONF_ROUTE_LOCALNET. As commit d0daebc3d622 ("ipv4: Add
interface option to enable routing of 127.0.0.0/8") intended, the cache
flush should only be performed when ROUTE_LOCALNET changes from 1 to 0.
Unfortunately, this was not true because while implementing it the
DEVINET_SYSCTL_FLUSHING_ENTRY was used for the attribute, making the
code related to it on devinet_conf_proc() dead.

IPV4_DEVCONF_FORWARDING is still being handled separately as it requires
more operations.

Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
Note: I ripped of the previous version tag because the patch is now
something completely different given the rework of devconf sysctl
handling
---
 net/ipv4/devinet.c | 127 ++++++++++++++++++++++++---------------------
 1 file changed, 68 insertions(+), 59 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 58fe7cb69545..c81bb948d59f 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -2500,6 +2500,46 @@ static int devinet_conf_ifindex(struct net *net, struct ipv4_devconf *cnf)
 	}
 }
 
+static bool devinet_conf_post_set(struct net *net, struct ipv4_devconf *cnf,
+				  int attr, int new, int old, int ifindex)
+{
+	if (new == old)
+		return false;
+
+	switch (attr) {
+	case IPV4_DEVCONF_ROUTE_LOCALNET:
+	case IPV4_DEVCONF_ACCEPT_LOCAL:
+		if (new == 0)
+			return true;
+		break;
+	case IPV4_DEVCONF_NOXFRM:
+	case IPV4_DEVCONF_NOPOLICY:
+	case IPV4_DEVCONF_PROMOTE_SECONDARIES:
+	case IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST:
+	case IPV4_DEVCONF_BC_FORWARDING:
+		return true;
+	case IPV4_DEVCONF_RP_FILTER:
+		inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
+					    NETCONFA_RP_FILTER,
+					    ifindex, cnf);
+		break;
+	case IPV4_DEVCONF_PROXY_ARP:
+		inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
+					    NETCONFA_PROXY_NEIGH,
+					    ifindex, cnf);
+		break;
+	case IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN:
+		inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
+					    NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
+					    ifindex, cnf);
+		break;
+	default:
+		break;
+	}
+
+	return false;
+}
+
 static int devinet_conf_proc(const struct ctl_table *ctl, int write,
 			     void *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -2509,44 +2549,31 @@ static int devinet_conf_proc(const struct ctl_table *ctl, int write,
 
 	if (write) {
 		struct ipv4_devconf *cnf = ctl->extra1;
-		struct net *net = ctl->extra2;
 		int i = (int *)ctl->data - cnf->data;
+		struct net *net = ctl->extra2;
 		int ifindex;
 
-		set_bit(i, cnf->state);
-
-		if (cnf == net->ipv4.devconf_dflt)
-			devinet_copy_dflt_conf(net, i);
-		if (i == IPV4_DEVCONF_ACCEPT_LOCAL - 1 ||
-		    i == IPV4_DEVCONF_ROUTE_LOCALNET - 1)
-			if ((new_value == 0) && (old_value != 0))
-				rt_cache_flush(net);
+		/* These attributes are bypassing the tracking state,
+		 * for the rest track the state and propagate the changes
+		 * to default config
+		 */
+		switch (i + 1) {
+		case IPV4_DEVCONF_NOXFRM:
+		case IPV4_DEVCONF_NOPOLICY:
+		case IPV4_DEVCONF_PROMOTE_SECONDARIES:
+		case IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST:
+			break;
+		default:
+			set_bit(i, cnf->state);
+			if (cnf == net->ipv4.devconf_dflt)
+				devinet_copy_dflt_conf(net, i);
+			break;
+		}
 
-		if (i == IPV4_DEVCONF_BC_FORWARDING - 1 &&
-		    new_value != old_value)
+		ifindex = devinet_conf_ifindex(net, cnf);
+		if (devinet_conf_post_set(net, cnf, i + 1, new_value,
+					  old_value, ifindex))
 			rt_cache_flush(net);
-
-		if (i == IPV4_DEVCONF_RP_FILTER - 1 &&
-		    new_value != old_value) {
-			ifindex = devinet_conf_ifindex(net, cnf);
-			inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
-						    NETCONFA_RP_FILTER,
-						    ifindex, cnf);
-		}
-		if (i == IPV4_DEVCONF_PROXY_ARP - 1 &&
-		    new_value != old_value) {
-			ifindex = devinet_conf_ifindex(net, cnf);
-			inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
-						    NETCONFA_PROXY_NEIGH,
-						    ifindex, cnf);
-		}
-		if (i == IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN - 1 &&
-		    new_value != old_value) {
-			ifindex = devinet_conf_ifindex(net, cnf);
-			inet_netconf_notify_devconf(net, RTM_NEWNETCONF,
-						    NETCONFA_IGNORE_ROUTES_WITH_LINKDOWN,
-						    ifindex, cnf);
-		}
 	}
 
 	return ret;
@@ -2599,20 +2626,6 @@ static int devinet_sysctl_forward(const struct ctl_table *ctl, int write,
 	return ret;
 }
 
-static int ipv4_doint_and_flush(const struct ctl_table *ctl, int write,
-				void *buffer, size_t *lenp, loff_t *ppos)
-{
-	int *valp = ctl->data;
-	int val = *valp;
-	int ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
-	struct net *net = ctl->extra2;
-
-	if (write && *valp != val)
-		rt_cache_flush(net);
-
-	return ret;
-}
-
 #define DEVINET_SYSCTL_ENTRY(attr, name, mval, proc) \
 	{ \
 		.procname	= name, \
@@ -2633,9 +2646,6 @@ static int ipv4_doint_and_flush(const struct ctl_table *ctl, int write,
 #define DEVINET_SYSCTL_COMPLEX_ENTRY(attr, name, proc) \
 	DEVINET_SYSCTL_ENTRY(attr, name, 0644, proc)
 
-#define DEVINET_SYSCTL_FLUSHING_ENTRY(attr, name) \
-	DEVINET_SYSCTL_COMPLEX_ENTRY(attr, name, ipv4_doint_and_flush)
-
 static struct devinet_sysctl_table {
 	struct ctl_table_header *sysctl_header;
 	struct ctl_table devinet_vars[IPV4_DEVCONF_MAX];
@@ -2678,15 +2688,14 @@ static struct devinet_sysctl_table {
 					"ignore_routes_with_linkdown"),
 		DEVINET_SYSCTL_RW_ENTRY(DROP_GRATUITOUS_ARP,
 					"drop_gratuitous_arp"),
-
-		DEVINET_SYSCTL_FLUSHING_ENTRY(NOXFRM, "disable_xfrm"),
-		DEVINET_SYSCTL_FLUSHING_ENTRY(NOPOLICY, "disable_policy"),
-		DEVINET_SYSCTL_FLUSHING_ENTRY(PROMOTE_SECONDARIES,
-					      "promote_secondaries"),
-		DEVINET_SYSCTL_FLUSHING_ENTRY(ROUTE_LOCALNET,
-					      "route_localnet"),
-		DEVINET_SYSCTL_FLUSHING_ENTRY(DROP_UNICAST_IN_L2_MULTICAST,
-					      "drop_unicast_in_l2_multicast"),
+		DEVINET_SYSCTL_RW_ENTRY(NOXFRM, "disable_xfrm"),
+		DEVINET_SYSCTL_RW_ENTRY(NOPOLICY, "disable_policy"),
+		DEVINET_SYSCTL_RW_ENTRY(PROMOTE_SECONDARIES,
+					"promote_secondaries"),
+		DEVINET_SYSCTL_RW_ENTRY(ROUTE_LOCALNET,
+					"route_localnet"),
+		DEVINET_SYSCTL_RW_ENTRY(DROP_UNICAST_IN_L2_MULTICAST,
+					"drop_unicast_in_l2_multicast"),
 	},
 };
 
-- 
2.53.0


^ permalink raw reply related	[flat|nested] 6+ messages in thread
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2026-03-25 16:10 [PATCH 1/2 net-next] ipv4: centralize devconf sysctl handling Fernando Fernandez Mancera
2026-03-25 16:10 ` [PATCH 2/2 net-next] ipv4: ipv4: handle devconf post-set actions on netlink updates Fernando Fernandez Mancera
2026-03-25 20:39   ` Fernando Fernandez Mancera
2026-03-26  3:39   ` kernel test robot
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