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Date:   Wed, 31 Mar 2021 12:58:52 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
Cc:     netfilter-devel@vger.kernel.org, pablo@netfilter.org, fw@strlen.de
Subject: Re: [iptables PATCH v3 2/2] extensions: libxt_conntrack: print xlate
 status as set
Message-ID: <20210331105852.GD17285@breakpoint.cc>
References: <20210331102934.848126-1-alexander.mikhalitsyn@virtuozzo.com>
 <20210331102934.848126-2-alexander.mikhalitsyn@virtuozzo.com>
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Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com> wrote:
> At the moment, status_xlate_print function prints statusmask as comma-separated
> sequence of enabled statusmask flags. But if we have inverted conntrack ctstatus
> condition then we have to use more complex expression (if more than one flag enabled)
> because nft not supports syntax like "ct status != expected,assured".
> 
> Examples:
> ! --ctstatus CONFIRMED,ASSURED
> should be translated as
> ct status & (assured|confirmed) == 0
> 
> ! --ctstatus CONFIRMED
> can be translated as
> ct status != confirmed

"! --ctstatus CONFIRMED" means 'true if CONFIRMED bit is not set'
But "ct status != confirmed" means 'true if ct status contains any value
except confirmed.

Example: ct->status has confirmed and assured bits set.
Then:
"! --ctstatus CONFIRMED" won't match (the bit is set).
ct status != confirmed returns true (3 != 1)
ct (status & confirmed) == 0 won't match (the bit is set).