Adjust bpf event filter

[Visa Hankala]

This makes bpf(4) use knote_modify_fn() and knote_process_fn().

Since the code has only one event function, it makes sense to use it
directly instead of going through struct filterops f_event pointer.

OK?

Index: net/bpf.c
===================================================================
RCS file: src/sys/net/bpf.c,v
retrieving revision 1.214
diff -u -p -r1.214 bpf.c
--- net/bpf.c   13 Feb 2022 23:11:10 -0000      1.214
+++ net/bpf.c   14 Feb 2022 08:08:07 -0000
@@ -1229,8 +1229,13 @@ filt_bpfrdetach(struct knote *kn)
 }
 
 int
-filt_bpfread_common(struct knote *kn, struct bpf_d *d)
+filt_bpfread(struct knote *kn, long hint)
 {
+       struct bpf_d *d = kn->kn_hook;
+
+       if (hint == NOTE_SUBMIT) /* ignore activation from selwakeup */
+               return (0);
+
        MUTEX_ASSERT_LOCKED(&d->bd_mtx);
 
        kn->kn_data = d->bd_hlen;
@@ -1241,25 +1246,13 @@ filt_bpfread_common(struct knote *kn, st
 }
 
 int
-filt_bpfread(struct knote *kn, long hint)
-{
-       struct bpf_d *d = kn->kn_hook;
-
-       if (hint == NOTE_SUBMIT) /* ignore activation from selwakeup */
-               return (0);
-
-       return (filt_bpfread_common(kn, d));
-}
-
-int
 filt_bpfreadmodify(struct kevent *kev, struct knote *kn)
 {
        struct bpf_d *d = kn->kn_hook;
        int active;
 
        mtx_enter(&d->bd_mtx);
-       knote_assign(kev, kn);
-       active = filt_bpfread_common(kn, d);
+       active = knote_modify_fn(kev, kn, filt_bpfread);
        mtx_leave(&d->bd_mtx);
 
        return (active);
@@ -1272,12 +1265,7 @@ filt_bpfreadprocess(struct knote *kn, st
        int active;
 
        mtx_enter(&d->bd_mtx);
-       if (kev != NULL && (kn->kn_flags & EV_ONESHOT))
-               active = 1;
-       else
-               active = filt_bpfread_common(kn, d);
-       if (active)
-               knote_submit(kn, kev);
+       active = knote_process_fn(kn, kev, filt_bpfread);
        mtx_leave(&d->bd_mtx);
 
        return (active);