netdev - Re: [PATCH net 2/5] netfilter: nf_tables: add position handle in event notification

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Date:   Thu, 30 Sep 2021 15:49:46 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     David Miller <davem@...emloft.net>
Cc:     kuba@...nel.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net 2/5] netfilter: nf_tables: add position handle in
 event notification

On Thu, Sep 30, 2021 at 01:35:22PM +0100, David Miller wrote:
> From: Jakub Kicinski <kuba@...nel.org>
> Date: Wed, 29 Sep 2021 19:19:53 -0700
> 
> > On Thu, 30 Sep 2021 01:04:57 +0200 Pablo Neira Ayuso wrote:
> >> Add position handle to allow to identify the rule location from netlink
> >> events. Otherwise, userspace cannot incrementally update a userspace
> >> cache through monitoring events.
> >> 
> >> Skip handle dump if the rule has been either inserted (at the beginning
> >> of the ruleset) or appended (at the end of the ruleset), the
> >> NLM_F_APPEND netlink flag is sufficient in these two cases.
> >> 
> >> Handle NLM_F_REPLACE as NLM_F_APPEND since the rule replacement
> >> expansion appends it after the specified rule handle.
> >> 
> >> Fixes: 96518518cc41 ("netfilter: add nftables")
> >> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> > 
> > Let me defer to Dave on this one. Krzysztof K recently provided us with
> > this quote:
> > 
> > "One thing that does bother [Linus] is developers who send him fixes in the
> > -rc2 or -rc3 time frame for things that never worked in the first place.
> > If something never worked, then the fact that it doesn't work now is not
> > a regression, so the fixes should just wait for the next merge window.
> > Those fixes are, after all, essentially development work."
> > 
> > 	https://lwn.net/Articles/705245/
> > 
> > Maybe the thinking has evolved since, but this patch strikes me as odd.
> > We forgot to put an attribute in netlink 8 years ago, and suddenly it's
> > urgent to fill it in?  Something does not connect for me, certainly the
> > commit message should have explained things better...
> 
> Agreed.

The aforementioned article says:

"In general, he said, if a fix applies to a feature that is not
currently being used, it should wait for the next development cycle"

This feature is being used by 'nft monitor', which is not
representing:

- insert rule
- add/insert rule with position handle
- create table/chain/set/map

commands in the correct way via netlink notifications.

I can rework the commit message to clarify this and resubmit.