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

[Kris Van Hees]

On Sun, Sep 14, 2025 at 12:18:20PM +0100, Nick Alcock via DTrace-devel wrote:
> 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.

OK, I will mark it as NAK so it gets removed from my tracking.

> >> 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)
> 
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