netdev - Re: [PATCH iproute2] tc: util: constrain percentage in 0-100 interval

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Date:   Mon, 15 Jul 2019 13:48:20 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Andrea Claudi <aclaudi@...hat.com>
Cc:     netdev@...r.kernel.org, dsahern@...nel.org
Subject: Re: [PATCH iproute2] tc: util: constrain percentage in 0-100
 interval

On Sat, 13 Jul 2019 11:44:07 +0200
Andrea Claudi <aclaudi@...hat.com> wrote:

> parse_percent() currently allows to specify negative percentages
> or value above 100%. However this does not seems to make sense,
> as the function is used for probabilities or bandiwidth rates.
> 
> Moreover, using negative values leads to erroneous results
> (using Bernoulli loss model as example):
> 
> $ ip link add test type dummy
> $ ip link set test up
> $ tc qdisc add dev test root netem loss gemodel -10% limit 10
> $ tc qdisc show dev test
> qdisc netem 800c: root refcnt 2 limit 10 loss gemodel p 90% r 10% 1-h 100% 1-k 0%
> 
> Using values above 100% we have instead:
> 
> $ ip link add test type dummy
> $ ip link set test up
> $ tc qdisc add dev test root netem loss gemodel 140% limit 10
> $ tc qdisc show dev test
> qdisc netem 800f: root refcnt 2 limit 10 loss gemodel p 40% r 60% 1-h 100% 1-k 0%
> 
> This commit changes parse_percent() with a check to ensure
> percentage values stay between 1.0 and 0.0.
> parse_percent_rate() function, which already employs a similar
> check, is adjusted accordingly.
> 
> With this check in place, we have:
> 
> $ ip link add test type dummy
> $ ip link set test up
> $ tc qdisc add dev test root netem loss gemodel -10% limit 10
> Illegal "loss gemodel p"
> 
> Fixes: 927e3cfb52b58 ("tc: B.W limits can now be specified in %.")
> Signed-off-by: Andrea Claudi <aclaudi@...hat.com>

Looks good. Applied