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

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Date:   Tue, 10 Jul 2018 13:28:34 +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



On 07/10/2018 04:20 AM, Jesper Dangaard Brouer wrote:
> On Tue, 10 Jul 2018 02:44:06 +0900
> Taeung Song <treeze.taeung@...il.com> wrote:
> 
>> 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.
> 
> The 'basename' does not work correctly if e.g. TC='sudo tc'.
> 
> Below output is with 'basename' removed, else it would say "sudo qdisc del ..."
> 
> TC='sudo tc' IP='sudo ip' ./xdp2skb_meta.sh -v --dev mlx5p1 --dry-run
> # Device set to: DEV=mlx5p1
> # Dry-run mode: enable VERBOSE and don't call TC+IP
> sudo tc qdisc del dev mlx5p1 clsact
> sudo tc qdisc add dev mlx5p1 clsact
> sudo tc filter add dev mlx5p1 ingress prio 1 handle 1 bpf da obj ./xdp2skb_meta_kern.o sec tc_mark
> # Flush XDP on device: mlx5p1
> sudo ip link set dev mlx5p1 xdp off
> sudo ip link set dev mlx5p1 xdp obj ./xdp2skb_meta_kern.o sec xdp_mark
> 
> 

Oops, right. I missed the alias case.

>> But it seems to be trivial, I'll resend this patch as v2 based on your
>> comment !
> 
> Thx, already ACKed it :-)
> 

--
Thanks a lot !

Taeung