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

[xuyang2018.jy@fujitsu.com]

Hi Richard,Li

Today, I try it again by adding two cgroup functions and succeed by 
using at* syscalls(I like at* syscalls because they are so convient). I 
will send patch set to mail list tomorrow.

+int safe_cg_open(const char *const file, const int lineno,
+                       const struct tst_cg_group *cg,
+                       const char *const file_name, int flags)
+{
+       const struct cgroup_file *const cfile =
+               cgroup_file_find(file, lineno, file_name);
+       struct cgroup_dir *const *dir;
+       const char *alias;
+       int fd;
+
+       for_each_dir(cg, cfile->ctrl_indx, dir) {
+               alias = cgroup_file_alias(cfile, *dir);
+               if (!alias)
+                       continue;
+
+               fd = safe_openat(file, lineno, (*dir)->dir_fd, alias, 
flags);
+       }
+
+       return fd;
+}
+
+void safe_cg_fchown(const char *const file, const int lineno,
+                       const struct tst_cg_group *cg,
+                       const char *const file_name, uid_t owner, gid_t 
group)
+{
+       const struct cgroup_file *const cfile =
+               cgroup_file_find(file, lineno, file_name);
+       struct cgroup_dir *const *dir;
+       const char *alias;
+
+       for_each_dir(cg, cfile->ctrl_indx, dir) {
+               alias = cgroup_file_alias(cfile, *dir);
+               if (!alias)
+                       continue;
+
+
+                safe_fchownat(file, lineno, (*dir)->dir_fd, alias, 
owner, group, 0);
+        }
+}
+

Best Regards
Yang Xu

> Hi  Richard
>> 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.
>>
> 
> Yes, this bug exists on both v1 and v2.
> 
>> 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.
>>
> 
> Thanks, I will try this.
> 
> Best Regards
> Yang Xu
>>>> 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
>>
>>
>