Re: [PATCH net] netlink: specs: rt-link: fix ipv6 devconf doc

[Paolo Abeni <pabeni@redhat.com>]

On 8/24/26 12:38 PM, Asbjørn Sloth Tønnesen wrote:
> devconf is even odder than described in the blamed commit, where bpth
> IPv4 and IPv6 are described in an identical way:
> "u32 indexed by ipv?-devconf - 1 on output, on input it's a nest".
> 
> There are two issues with that line for IPv6:
> 
> 1) The subtraction is an IPv4 specific quirk, to avoid having an unused
>    u32 at index 0, thus saving 4 bytes per net device being dumped:
> 
>    - In include/uapi/linux/ip.h the IPV4_DEVCONF_* enum begins with
>      IPV4_DEVCONF_FORWARDING = 1, so the enum starts at 1, which is
>      the reason for the subtraction in the IPv4 variant.
> 
>    - In include/uapi/linux/ipv6.h the DEVCONF_* enum begins with
>      DEVCONF_FORWARDING = 0, so subtraction would underflow.
> 
>    - ipv6_store_devconf() in net/ipv6/addrconf.c also doesn't do the
>      subtraction in the output path.
> 
> 2) Setting IPv6 devconf through Netlink is not yet supported, as
>    IFLA_INET6_CONF is not handled in inet6_set_link_af().
> 
> Fixes: 720447bd0b24 ("netlink: specs: rt-link: remove implicit structs from devconf")
> Cc: stable@vger.kernel.org
> Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Nowadays net PRs are already too big due more-or-less security-relevant
changes. I think this is better suited for net-next, with no 'fixes' tag
nor stable cc, WDYT?

/P