Re: [PATCH 2/2] vfs: Add KUnit tests for fdtable

[Christian Brauner]

On Wed, Aug 12, 2026 at 05:06:37PM +0200, Jann Horn wrote:
> On Wed, Aug 12, 2026 at 2:22 AM Kees Cook <kees@xxxxxxxxxx> wrote:
> > On Tue, Aug 11, 2026 at 05:42:05PM +0200, Jann Horn wrote:
> > > On Tue, Aug 11, 2026 at 2:16 AM Kees Cook <kees@xxxxxxxxxx> wrote:
> > > > On Mon, Aug 10, 2026 at 08:41:13PM +0000, Bill Wendling wrote:
> > > > > +static void fdtable_test_alloc(struct kunit *test)
> > > > > +{
> > > > > +     struct fdtable *fdt;
> > > > > +     unsigned int slots = 64;
> > > > > +
> > > > > +     fdt = alloc_fdtable(slots);
> > > > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fdt);
> > > > > +
> > > > > +     /* Check that max_fds is set correctly and is >= slots */
> > > > > +     KUNIT_EXPECT_GE(test, fdt->max_fds, slots);
> > > > > +
> > > > > +     /* Check that fd is allocated */
> > > > > +     KUNIT_EXPECT_NOT_ERR_OR_NULL(test, fdt->fd);
> > > >
> > > > Nice to add these tests! Can you add one for each of the conditionals
> > > > in alloc_fdtable (e.g. ENOMEM, EMFILE, and the power-of-two rounding-up
> > > > logic, etc)?
> > >
> > > Wouldn't tests for stuff like the rounding-up logic get into
> > > implementation details too much, and break if implementation choices
> > > change?
> >
> > It seemed to me like we'd want to notice if that behavior changed?
> 
> Why?
> File descriptor tables are often power-of-two sized, but they aren't
> always. That is an implementation choice that doesn't impact
> correctness, it just affects performance somewhat. So I don't see what
> the point of a test for this would be - it seems like it would just be
> in the way of making changes, a "Change-Detector Test"?

Yeah, I don't think this makes much sense.