[RESEND PATCH v3] Babel: allow choosing link quality estimation algorithm

[Toke Høiland-Jørgensen]

Nick Cao via Bird-users <bird-users at network.cz> writes:

> Resend of the patch in http://trubka.network.cz/pipermail/bird-users/2023-June/017058.html
>
> ETX link quality estimation algorithm is useful for link types other than wireless,
> especially when using babel with tunnels where packet losses do occur.
> ---
>  doc/bird.sgml        | 10 ++++++++++
>  proto/babel/babel.c  |  8 +++-----
>  proto/babel/babel.h  |  8 ++++++++
>  proto/babel/config.Y |  8 +++++++-
>  4 files changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/doc/bird.sgml b/doc/bird.sgml
> index f2063325..1a9bab87 100644
> --- a/doc/bird.sgml
> +++ b/doc/bird.sgml
> @@ -2209,6 +2209,7 @@ protocol babel [<name>] {
>  		rx buffer <number>;
>  		tx length <number>;
>  		check link <switch>;
> +		link quality <none|etx>;
>  		next hop ipv4 <address>;
>  		next hop ipv6 <address>;
>  		extended next hop <switch>;
> @@ -2312,6 +2313,15 @@ protocol babel [<name>] {
>        hardware drivers or platforms do not implement this feature. Default:
>        yes.
>  
> +      <tag><label id="babel-link-quality">link quality none|etx </tag>
> +      This option specifies the link quality estimation algorithm for computing
> +      costs based on Hello history: none or etx. The none (k-out-of-j) algorithm
> +      is suitable for wired links that are either up, in which case they only
> +      occasionally drop a packet, or down, in which case they drop all packets.
> +      The Expected Transmission Cost algorithm, or etx, is suitable for wireless
> +      links that exhibit continuous variation of the link quality. Default: etx for
> +      wireless interfaces, none otherwise.
> +
>        <tag><label id="babel-next-hop-ipv4">next hop ipv4 <m/address/</tag>
>        Set the next hop address advertised for IPv4 routes advertised on this
>        interface. Default: the preferred IPv4 address of the interface.
> diff --git a/proto/babel/babel.c b/proto/babel/babel.c
> index 4187d258..f865c089 100644
> --- a/proto/babel/babel.c
> +++ b/proto/babel/babel.c
> @@ -593,10 +593,9 @@ babel_update_cost(struct babel_neighbor *nbr)
>    if (!rcv || !nbr->ifa->up)
>      goto done;
>  
> -  switch (cf->type)
> +  switch (cf->link_quality)
>    {
> -  case BABEL_IFACE_TYPE_WIRED:
> -  case BABEL_IFACE_TYPE_TUNNEL:
> +  case BABEL_IFACE_LINK_QUALITY_NONE:

Sorry for missing this earlier, but it looks like with your patch bird
will no longer honour the "wires" or "wireless" setting at all? Which
will break old configs, so please don't do that.

The right way to do this is to have "wired" and "wireless" serve as
"presets", and then have the link quality override that setting. So that
just setting "wireless" will get the same settings as today, but setting
"wired + etx" will get you just the ETX setting.

-Toke