netdev - Re: [v2 2/3] samples: pktgen: add helper functions for IP(v4/v6) CIDR parsing

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Message-ID: <CAEKGpzjgp2+XLd340MRPJ9FSHPusb13zjZafTvRrSuRy3kOgjw@mail.gmail.com>
Date:   Sun, 15 Sep 2019 00:02:37 +0900
From:   "Daniel T. Lee" <danieltimlee@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [v2 2/3] samples: pktgen: add helper functions for IP(v4/v6) CIDR parsing

On Fri, Sep 13, 2019 at 9:43 PM Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
>
> On Thu, 12 Sep 2019 03:48:06 +0900
> "Daniel T. Lee" <danieltimlee@...il.com> wrote:
>
> > This commit adds CIDR parsing and IP validate helper function to parse
> > single IP or range of IP with CIDR. (e.g. 198.18.0.0/15)
> >
> > Helpers will be used in prior to set target address in samples/pktgen.
> >
> > Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> > ---
> >  samples/pktgen/functions.sh | 122 ++++++++++++++++++++++++++++++++++++
> >  1 file changed, 122 insertions(+)
> >
> > diff --git a/samples/pktgen/functions.sh b/samples/pktgen/functions.sh
> > index 4af4046d71be..8be5a6b6c097 100644
> [...]
>
> > +# Given a single IP(v4/v6) or CIDR, return minimum and maximum IP addr.
> > +function parse_addr()
> > +{
> > +    # check function is called with (funcname)6
> > +    [[ ${FUNCNAME[1]: -1} == 6 ]] && local IP6=6
> > +    local bitlen=$[ IP6 ? 128 : 32 ]
> > +    local octet=$[ IP6 ? 16 : 8 ]
> > +
> > +    local addr=$1
> > +    local net prefix
> > +    local min_ip max_ip
> > +
> > +    IFS='/' read net prefix <<< $addr
> > +    [[ $IP6 ]] && net=$(extend_addr6 $net)
> > +    validate_addr$IP6 $net
> > +
> > +    if [[ $prefix -gt $bitlen ]]; then
> > +        err 5 "Invalid prefix: $prefix"
> > +    elif [[ -z $prefix ]]; then
> > +        min_ip=$net
> > +        max_ip=$net
> > +    else
> > +        # defining array for converting Decimal 2 Binary
> > +        # 00000000 00000001 00000010 00000011 00000100 ...
> > +        local d2b='{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}'
> > +        [[ $IP6 ]] && d2b+=$d2b
> > +        eval local D2B=($d2b)
>
> I must say this is a rather cool shell/bash trick to use an array for
> converting decimal numbers into binary.
>

Thank you for the compliment and for the detailed review.

> > +
> > +        local shift=$[ bitlen-prefix ]
>
> Using a variable named 'shift' is slightly problematic for shell/bash
> code.  It works, but it is just confusing.
>
> > +        local min_mask max_mask
> > +        local min max
> > +        local ip_bit
> > +        local ip sep
> > +
> > +        # set separator for each IP(v4/v6)
> > +        [[ $IP6 ]] && sep=: || sep=.
> > +        IFS=$sep read -ra ip <<< $net
> > +
> > +        min_mask="$(printf '1%.s' $(seq $prefix))$(printf '0%.s' $(seq $shift))"
> > +        max_mask="$(printf '0%.s' $(seq $prefix))$(printf '1%.s' $(seq $shift))"
>
> Also a surprising shell trick to get binary numbers out of a prefix number.
>
> > +
> > +        # calculate min/max ip with &,| operator
> > +        for i in "${!ip[@]}"; do
> > +            digit=$[ IP6 ? 16#${ip[$i]} : ${ip[$i]} ]
> > +            ip_bit=${D2B[$digit]}
> > +
> > +            idx=$[ octet*i ]
> > +            min[$i]=$[ 2#$ip_bit & 2#${min_mask:$idx:$octet} ]
> > +            max[$i]=$[ 2#$ip_bit | 2#${max_mask:$idx:$octet} ]
> > +            [[ $IP6 ]] && { min[$i]=$(printf '%X' ${min[$i]});
> > +                            max[$i]=$(printf '%X' ${max[$i]}); }
> > +        done
> > +
> > +        min_ip=$(IFS=$sep; echo "${min[*]}")
> > +        max_ip=$(IFS=$sep; echo "${max[*]}")
> > +    fi
> > +
> > +    echo $min_ip $max_ip
> > +}
>
> If you just fix the variable name 'shift' to something else, then I'm
> happy with this patch.
>
> Again, I'm very impressed with your shell/bash skills, I were certainly
> challenged when reviewing this :-)
>

I'll change the variable name to 'remain'.

Once again, I really appreciate your time and effort for the review.
Thank you.

Best,
Daniel

> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer