[DTrace-devel] [PATCH 4/4] test: Do not depend on ext4

[Nick Alcock]

On 30 Oct 2024, Eugene Loh stated:

> E.g.,
>     $ uname -r
>     5.15.0-205.149.5.1.el9uek.aarch64
>     $ sudo grep ext4_dir_operations /proc/kallmodsyms
>      ffffc45a59d9ee88 100 D ext4_dir_operations
>      $ sudo awk '/ext4/ { print NF }' /proc/kallmodsyms | uniq -c
>        2342 4
>     $ sudo grep -w ext4 /proc/kallmodsyms

Something is presumably wrong there -- ext4 should always be considered
a built-in module if it's built in, that's what built-in modules *are*,
things that might be being built as modules but aren't.

i.e. this test is working as intended and pointing out a real bug :)
whether it's one we care about is another matter.

> So, lots of ext4 symbols (including ext4_dir_operations) but none of them are [ext4].  Bug in... kallmodsyms?
>
> On 10/25/24 17:16, Kris Van Hees wrote:
>> I am not too sure about this patch...  We are not using kallmodsyms anymore
>> for newer kernels, and on older kernels that symbol certainly be listed as
>> [ext4].  So, if ext4_dir_operations *is* in the ext4 module code (compiled in
>> or loadable), then the proper ref to it would be ext4`ext4_dir_operations.
>> So the test should be able to use that - if not, that seems like a bug rather
>> than something to change in the test?

Yes.

>> On Fri, Oct 04, 2024 at 12:43:55AM -0400, eugene.loh at oracle.com wrote:
>>> From: Eugene Loh <eugene.loh at oracle.com>
>>>
>>> It is possible that there is no ext4 module, whether built-in or otherwise,
>>> even if its symbols are present.  E.g.,

That wasn't true in the kallmodsyms world I wrote this for.

>>>      # grep ext4_dir_operations /proc/kallmodsyms
>>>      ffffc45a59d9ee88 100 D ext4_dir_operations
>>>      # grep -w ext4 /proc/kallmodsyms
>>>      #
>>>
>>> Meanwhile, in
>>>      ab883bae "tests, io, scalars: use kallsyms instead of kallmodsyms where possible"
>>> we read:
>>>      scalars/tst.misc.x needs adjusting to check for the presence of the actual
>>>      symbols we are looking up, since the modules might well be built-in, and
>>>      thus not show up in /proc/kallsyms.
>>>
>>> With that patch, in test/unittest/scalars/tst.misc.x, we check:
>>>     -if ! $(grep -qw ext4 /proc/kallmodsyms); then
>>>     +if ! grep -qw ext4_dir_operations /proc/kallsyms; then
>>>          exit 1
>>>      fi
>>>
>>> So it is possible for us to find
>>>          `ext4_dir_operations
>>> but not
>>>      ext4`ext4_dir_operations
>>>
>>> Change the .d script to look simply for `ext4_dir_operations.
>>>
>>> Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
>>> ---
>>>   test/unittest/scalars/tst.misc.d | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/test/unittest/scalars/tst.misc.d b/test/unittest/scalars/tst.misc.d
>>> index 60edab45e..6a5f4ae2e 100644
>>> --- a/test/unittest/scalars/tst.misc.d
>>> +++ b/test/unittest/scalars/tst.misc.d
>>> @@ -20,7 +20,7 @@
>>>   BEGIN
>>>   {
>>>   	printf("\nr_cpu_ids = 0x%x\n", `nr_cpu_ids);
>>> -	printf("ext4`ext4_dir_operations = %p\n", &ext4`ext4_dir_operations);
>>> +	printf("ext4`ext4_dir_operations = %p\n", &`ext4_dir_operations);
>>>   	printf("isofs`isofs_dir_operations = %p\n", &isofs`isofs_dir_operations);
>>>   	printf("vmlinux`major_names = %p\n", &vmlinux`major_names);
>>>   	x = 123;
>>> -- 2.43.5
>>>

-- 
NULL && (void)