Re: [LTP] Do we have some simple way to get the current cgroup.procs path?

[Richard Palethorpe <rpalethorpe@suse.de>]

Hello,

"xuyang2018.jy@fujitsu.com" <xuyang2018.jy@fujitsu.com> writes:

> Hi Li
>> Hi Xu,
>> 
>> On Thu, Jul 14, 2022 at 2:02 PM xuyang2018.jy@fujitsu.com 
>> <mailto:xuyang2018.jy@fujitsu.com> <xuyang2018.jy@fujitsu.com 
>> <mailto:xuyang2018.jy@fujitsu.com>> wrote:
>> 
>>     Hi Richard, LI
>> 
>>     I am writting a simple regression test[1]that refer to kernel
>>     selftest cgroup test_core[2]. I may name it as memcontrol05.c.
>> 
>>     It tests cgroup migration permission check should be performed based
>>     on the credentials at the time of open instead of write.
>> 
>>     I have used ltp cgroup framework, but ltp cgroup only use
>>     SAFE_CGROUP_PRINTF to write value.
>> 
>>     How can get the cgroup root_dir ltp_dir path? So I can open this fd
>>     and change/save effective uid between open and write?
>> 
>> Not sure if I fully understand your requirements.
>> Can we achieve this test by creating a two-layer subdirectory?
>
> I think yes.

I think you must have multiple layers. Otherwise you could break other
tests running in parallel.

>
>> 
>> Does only the root/ltp_dir mandatory for completing your test?
>
> It also need gettid subdirectory and cgroup name.

You could create an accessor function in the library to get dir_fd from
cgroup_dir.

This is complicated by V1 CGs where a tst_cg_group can have multiple
struct cgroup_dir's. This isn't a problem for selftests because they
only support V2, but it would be nice to make as many tests as possible
work with V1.

The easiest solution I can think of is to write a library function like
SAFE_CG_GROUP_EACH_DIR(void (*const fn_ptr)(int dir_fd)) which takes a
const function pointer and executes it with the FD of each
directory. Then you can use the internal for_each_dir macro like
SAFE_CGROUP_PRINTF.

>> If yes, I think tst_cg_print_config() maybe fits your purpose,
>> but that would need additional function help extracting that.
>> 
>> Take a reference to see how Luke gets the root path (in shell):
>> https://lists.linux.it/pipermail/ltp/2022-April/028772.html
>> <https://lists.linux.it/pipermail/ltp/2022-April/028772.html>
>
> Thanks, I prefer to use c api and will think about it continuely.
>
> Best Regards
> Yang Xu
>> 
>> 
>> -- 
>> Regards,
>> Li Wang


-- 
Thank you,
Richard.

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