Re: [PATCH net v4] ipv4: bump rt_genid when a relevant devconf value changes through netlink

[Fernando Fernandez Mancera <fmancera@suse.de>]

On 3/13/26 3:56 PM, David Ahern wrote:
> On 3/13/26 8:45 AM, Fernando Fernandez Mancera wrote:
>> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
>> index 537bb6c315d2..6dd8fd0a1323 100644
>> --- a/net/ipv4/devinet.c
>> +++ b/net/ipv4/devinet.c
>> @@ -2107,8 +2109,33 @@ static int inet_set_link_af(struct net_device *dev, const struct nlattr *nla,
>>   		return -EINVAL;
>>   
>>   	if (tb[IFLA_INET_CONF]) {
>> -		nla_for_each_nested(a, tb[IFLA_INET_CONF], rem)
>> -			ipv4_devconf_set(in_dev, nla_type(a), nla_get_u32(a));
>> +		nla_for_each_nested(a, tb[IFLA_INET_CONF], rem) {
>> +			int new_value = (int)nla_get_u32(a);
>> +
>> +			if (ipv4_devconf_get(in_dev, nla_type(a)) == new_value)
>> +				continue;
>> +
>> +			ipv4_devconf_set(in_dev, nla_type(a), new_value);
>> +			switch (nla_type(a)) {
>> +			case IPV4_DEVCONF_FORWARDING:
>> +				if (new_value)
>> +					netif_disable_lro(dev);
>> +				fallthrough;
>> +			case IPV4_DEVCONF_NOXFRM:
>> +			case IPV4_DEVCONF_NOPOLICY:
>> +			case IPV4_DEVCONF_PROMOTE_SECONDARIES:
>> +			case IPV4_DEVCONF_ROUTE_LOCALNET:
>> +			case IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST:
>> +			case IPV4_DEVCONF_BC_FORWARDING:
>> +			case IPV4_DEVCONF_ACCEPT_LOCAL:
>> +				flush_cache = true;
>> +				break;
>> +			default:
>> +				break;
>> +			}
>> +		}
>> +		if (flush_cache)
>> +			rt_cache_flush(net);
>>   	}
>>   
>>   	return 0;
> 

Hi David,

> This replicates logic in devinet_conf_proc for example. Why not refactor
> devinet.c to handle changes to values in 1 place only.

I have been looking into it but seems like too much to do it on the net 
tree. I am preparing a patch for IPv4 unifying the logic as much as 
possible so we can get rid of this mess.

> Also, you are flushing the cache for more values than sysfs does.

I don't think so. The problem is that the handling of sysctl is 
scattered in several places.

IPV4_DEVCONF_FORWARDING is flushed at devinet_sysctl_forward().

IPV4_DEVCONF_NOXFRM, IPV4_DEVCONF_NOPOLICY, 
IPV4_DEVCONF_PROMOTE_SECONDARIES, IPV4_DEVCONF_ROUTE_LOCALNET, and 
IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST are flushed at 
ipv4_doint_and_flush() used by macro DEVINET_SYSCTL_FLUSHING_ENTRY.

Finally, IPV4_DEVCONF_BC_FORWARDING and IPV4_DEVCONF_ACCEPT_LOCAL are 
flushed at devinet_conf_proc().

Yes, I know, the fact that they are scattered around is quite confusing. 
This could be all unified in a single place but that would be too much 
for net tree IMHO.

Please let me know if I am missing something.

Thanks,
Fernando.