netdev - Re: [PATCH] iptables: flush stdout after every verbose log.

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Message-ID: <CAHo-OoxP6ZrvbXFH_tC9_wdVDg7y=8bzVY9oKZTieZL_mqS1NQ@mail.gmail.com>
Date:   Mon, 27 Apr 2020 17:14:24 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Florian Westphal <fw@...len.de>,
        Linux Network Development Mailing List 
        <netdev@...r.kernel.org>,
        Netfilter Development Mailing List 
        <netfilter-devel@...r.kernel.org>
Subject: Re: [PATCH] iptables: flush stdout after every verbose log.

> Could you check if this slows down iptables-restore?

per the iptables-restore man page
       -v, --verbose
              Print additional debug info during ruleset processing.

Well, if you run it with verbose mode enabled you probably don't care
about performance all that much...
And it only does anything if you're feeding in comments, which again -
is unlikely.

iptables-save produces two comment lines per table, so you're likely
to have a grand total of 8 of these lines
(if you have raw/nat/mangle/filter tables all listed), and if you feed
that in to iptables-restore -v then
you end up calling flush 8 times, which triggers 8 extra write()
syscalls - which aren't exactly expensive to begin with...

So I think this is a non issue.

(I could change it so that only "#PING" flushes, which is the actual
comment netd sends for healthchecking,
but I just don't think it matters)