Re: [PATCH bpf-next v2 1/6] kallsyms: Add KALLSYMS_QUERY ioctl to /proc/kallsyms

[Samuel Wu]

On Wed, Nov 4, 2026 at 6:23 AM David Laight
<david.laight.linux@xxxxxxxxx> wrote:
>
> On Tue, 3 Nov 2026 17:14:26 -0800
> Samuel Wu <wusamuel@xxxxxxxxxx> wrote:
>
> > On Fri, Oct 30, 2026 at 3:02 AM David Laight
> > <david.laight.linux@xxxxxxxxx> wrote:
> > >
> > > On Thu, 29 Oct 2026 15:05:45 -0700
> > > Samuel Wu <wusamuel@xxxxxxxxxx> wrote:
> > [...]
> > > > BY_NAME matches names exactly, like kallsyms_lookup_name(), so they
> > > > would be different symbols at different addresses. Please correct me
> > > > if I'm missing something here!
> > >
> > > Only that the user might really want one of the copies.
> > > Sometimes there is only the copy.
> >
> > Good point. I'll have v3 add KALLSYMS_F_PREFIX + pos/next_pos
> > pagination to cover these. A prefix query for "foo." also finds the
> > copies when plain foo does not exist (expanded on this in my reply to
> > Andrii's Oct 30 mail in this thread).
>
> I'm busy rebasing my patches - they got stamped all over :-(
> I should get a v3 that applies by the end of the week.
>
> I will add a 'prefix' variant for you.
> The 'next symbol matches' flag is exactly that (actually it is a
> this symbol is a duplicate to avoid issues at the start of the array).
> So in this case that application would always need to read
> the next symbol (by name).

Thanks, that would be helpful. For my v3, I'll keep the lower_bound()
approach so the two series stay independent, but I can switch over
once your series lands, so there is only one search over the name
table.

> I think it might be more sensible (less pitfalls later on) to return
> the symbol number - not that of the next one.

What pitfalls were you anticipating? If the current symbol's position
is returned, userspace needs another ioctl() call and an -ENOENT
check, to learn that there are no more matches. Alternatively,
returning the next position means every call pays for a look-ahead,
which for an unfiltered query walks the module symbols even when
userspace only wants the first match.

Andrii, do you have a preference between the two?