netdev - Re: [PATCH 1/4] net: arp: introduce arp_evict

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Date:   Thu, 14 Oct 2021 09:59:45 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     James Prestwood <prestwoj@...il.com>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH 1/4] net: arp: introduce arp_evict_nocarrier sysctl
 parameter

On Thu, 14 Oct 2021 09:29:05 -0700 James Prestwood wrote:
> > > diff --git a/include/linux/inetdevice.h
> > > b/include/linux/inetdevice.h
> > > index 53aa0343bf69..63180170fdbd 100644
> > > --- a/include/linux/inetdevice.h
> > > +++ b/include/linux/inetdevice.h
> > > @@ -133,6 +133,7 @@ static inline void ipv4_devconf_setall(struct
> > > in_device *in_dev)
> > >  #define IN_DEV_ARP_ANNOUNCE(in_dev)    IN_DEV_MAXCONF((in_dev),
> > > ARP_ANNOUNCE)
> > >  #define IN_DEV_ARP_IGNORE(in_dev)      IN_DEV_MAXCONF((in_dev),
> > > ARP_IGNORE)
> > >  #define IN_DEV_ARP_NOTIFY(in_dev)      IN_DEV_MAXCONF((in_dev),
> > > ARP_NOTIFY)
> > > +#define IN_DEV_ARP_EVICT_NOCARRIER(in_dev)
> > > IN_DEV_CONF_GET((in_dev), ARP_EVICT_NOCARRIER)  
> > 
> > IN_DEV_ANDCONF() makes most sense, I'd think.  
> 
> So given we want '1' as the default as well as the ability to toggle
> this option per-netdev I thought this was more appropriate. One caviat
> is this would not work for setting ALL netdev's, but I don't think this
> is a valid use case; or at least I can't imagine why you'd want to ever
> do this.
> 
> This is a whole new area to me though, so if I'm understanding these
> macros wrong please educate me :)

Yeah, TBH I'm not sure what the best practice is here. I know we
weren't very consistent in the past. Having a knob for "all" which 
is 100% ignored seems like the worst option. Let me CC Dave Ahern,
please make sure you CC him on v2 as well.