[LTP] [PATCH] containers/netns/netns_sysfs.sh: add kernel version check

[Jiri Jaburek]

On 10/31/16 10:28, Cyril Hrubis wrote:
> Hi!
>>> +tst_kvercmp 2 6 35
>>> +if [ $? -eq 0 ]; then
>>
>> Just out of curiosity - I see this used on more places, but can't
>> understand why would you use this instead of simply
>>
>>   if tst_kvercmp 2 6 35; then
>>
>> Any reason behind that? Am I missing a test writing rule?
> 
> The most probable reason would be that the tst_kvercmp actually returns
> ternary result (older than, equal or newer is mapped to 0, 1, 2) so if
> you want to anything else than "kernel is older" check you have to
> examine the $?.
> 
> Maybe I sould write a new tst_kvercmp for the new shell library that
> would work similar to the test shell buildin so that we can do something
> as:
> 
> if tst_kvercmp -nq "2.6.35" -o "3.8"; then
> 	...
> fi
> 
> where the modifiers would stand for:
> 
> n  newer
> nq newer or equal
> o  older
> oq older or equal

If you're going to use letters for this, I suggest re-using what the
'test' a.k.a. '[' command has: -eq, -lt, -ge, -ne, etc.

If multiple options (like in your example) are supported, re-using the
logic from 'test' could also be a good idea: -a (and), -o (or), although
shell-based && or || might be more obvious.

if tst_kvercmp -ge "2.6.35" -a -lt "3.8"; then ...

if tst_kvercmp -ge "2.6.35" && tst_kvercmp -lt "3.8"; then ...

>