netdev - Re: [PATCH] samples/bpf: Fix tc and ip path in xdp2skb

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Date:   Tue, 10 Jul 2018 02:44:06 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] samples/bpf: Fix tc and ip path in xdp2skb_meta.sh

Hi Jesper Dangaard Brouer,

On 07/10/2018 12:40 AM, Jesper Dangaard Brouer wrote:
> On Tue, 10 Jul 2018 00:04:18 +0900
> Taeung Song <treeze.taeung@...il.com> wrote:
> 
>> The below path error can occur:
>>
>>    # ./xdp2skb_meta.sh --dev eth0 --list
>>    ./xdp2skb_meta.sh: line 61: /usr/sbin/tc: No such file or directory
>>
>>    # which tc
>>    /sbin/tc
>>
>> So use 'which' command instead of absolute path of tc and ip
>>
>> Fixes: 36e04a2d78d9 ("samples/bpf: xdp2skb_meta shows transferring info from XDP to SKB")
>> Cc: Jesper Dangaard Brouer <brouer@...hat.com>
>> Signed-off-by: Taeung Song <treeze.taeung@...il.com>
>> ---
>>   samples/bpf/xdp2skb_meta.sh | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/samples/bpf/xdp2skb_meta.sh b/samples/bpf/xdp2skb_meta.sh
>> index b9c9549c4c27..67cf7b5f336d 100755
>> --- a/samples/bpf/xdp2skb_meta.sh
>> +++ b/samples/bpf/xdp2skb_meta.sh
>> @@ -16,8 +16,8 @@
>>   BPF_FILE=xdp2skb_meta_kern.o
>>   DIR=$(dirname $0)
>>   
>> -export TC=/usr/sbin/tc
>> -export IP=/usr/sbin/ip
>> +export TC=`which tc`
>> +export IP=`which ip`
> 
> This is not a good solution, as 'which' can return something else.
> E.g. on my system I've aliased 'tc' to 'sudo tc', and `which tc` returns:
> 
> $ which tc
> alias tc='sudo tc'
> 	/usr/bin/sudo
> 
> The easiest solution is to simply do:
> 
>   export TC=tc
>   export IP=ip
> 
> The more fancy solution is to allow callers to redefine $IP and $TC:
> 
> [ -z "$TC" ] && TC=tc
> [ -z "$IP" ] && IP=ip
> 

Yep, you are right, I'll change it.

> And then you should also fix the use of 'basename', see below patch...
> 

I thought it'd be fine to leave 'basename' as it is,
because if callers redefine TC=/home/taeung/tc and give
the options --verbose or --dry-run, 'basename' can more tidily show outputs.

But it seems to be trivial, I'll resend this patch as v2 based on your 
comment !

Thanks,
Taeung