Re: [PATCH] samples/bpf: Fix tc and ip path in xdp2skb_meta.sh

[Taeung Song]

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@xxxxxxxxx> 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@xxxxxxxxxx>
> > Signed-off-by: Taeung Song <treeze.taeung@xxxxxxxxx>
> > ---
> >   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