Re: [PATCH v13 bpf-next 5/6] selftests/bpf: Add tests for filesystem kfuncs

[Song Liu <song@kernel.org>]

On Sun, Nov 26, 2023 at 6:09 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Nov 23, 2023 at 3:40 PM Song Liu <song@kernel.org> wrote:
> >
> > +static const char expected_value[] = "hello";
> > +char value[32];
> > +
> > +SEC("lsm.s/file_open")
> > +int BPF_PROG(test_file_open, struct file *f)
> > +{
> > +       struct bpf_dynptr value_ptr;
> > +       __u32 pid;
> > +       int ret;
> > +
> > +       pid = bpf_get_current_pid_tgid() >> 32;
> > +       if (pid != monitored_pid)
> > +               return 0;
> > +
> > +       bpf_dynptr_from_mem(value, sizeof(value), 0, &value_ptr);
> > +
> > +       ret = bpf_get_file_xattr(f, "user.kfuncs", &value_ptr);
> > +       if (ret != sizeof(expected_value))
> > +               return 0;
> > +       if (bpf_strncmp(value, ret, expected_value))
>
> Hmm. It doesn't work like:
> if (bpf_strncmp(value, ret, "hello"))

This also works. I used expected_value because there is a size
check above. We can also make do something like

if (ret != sizeof("hello"))
             return 0;
if (bpf_strncmp(value, ret, "hello"))
             return 0;

Both of the two work.

Thanks,
Song