Add EVFILT_EXCEPT filter for pipes

The kqueue-based select(2) needs the filter to replicate the old
exceptfds behaviour. The upcoming new poll(2) code will use the filter
for POLLHUP condition checking when the events bitmap is clear of
read/write events.

OK anton@

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index 280b475..3ece792 100644 (file)
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: sys_pipe.c,v 1.129 2021/10/24 06:59:54 visa Exp $     */
+/*     $OpenBSD: sys_pipe.c,v 1.130 2021/12/07 14:06:16 visa Exp $     */
 
 /*
  * Copyright (c) 1996 John S. Dyson
@@ -85,6 +85,10 @@ int  filt_pipewrite(struct knote *kn, long hint);
 int    filt_pipewritemodify(struct kevent *kev, struct knote *kn);
 int    filt_pipewriteprocess(struct knote *kn, struct kevent *kev);
 int    filt_pipewrite_common(struct knote *kn, struct pipe *rpipe);
+int    filt_pipeexcept(struct knote *kn, long hint);
+int    filt_pipeexceptmodify(struct kevent *kev, struct knote *kn);
+int    filt_pipeexceptprocess(struct knote *kn, struct kevent *kev);
+int    filt_pipeexcept_common(struct knote *kn, struct pipe *rpipe);
 
 const struct filterops pipe_rfiltops = {
        .f_flags        = FILTEROP_ISFD | FILTEROP_MPSAFE,
@@ -104,6 +108,15 @@ const struct filterops pipe_wfiltops = {
        .f_process      = filt_pipewriteprocess,
 };
 
+const struct filterops pipe_efiltops = {
+       .f_flags        = FILTEROP_ISFD | FILTEROP_MPSAFE,
+       .f_attach       = NULL,
+       .f_detach       = filt_pipedetach,
+       .f_event        = filt_pipeexcept,
+       .f_modify       = filt_pipeexceptmodify,
+       .f_process      = filt_pipeexceptprocess,
+};
+
 /*
  * Default pipe buffer size(s), this can be kind-of large now because pipe
  * space is pageable.  The pipe code will try to maintain locality of
@@ -908,6 +921,11 @@ pipe_kqfilter(struct file *fp, struct knote *kn)
                kn->kn_hook = wpipe;
                klist_insert_locked(&wpipe->pipe_sel.si_note, kn);
                break;
+       case EVFILT_EXCEPT:
+               kn->kn_fop = &pipe_efiltops;
+               kn->kn_hook = rpipe;
+               klist_insert_locked(&rpipe->pipe_sel.si_note, kn);
+               break;
        default:
                error = EINVAL;
        }
@@ -1047,6 +1065,65 @@ filt_pipewriteprocess(struct knote *kn, struct kevent *kev)
        return (active);
 }
 
+int
+filt_pipeexcept_common(struct knote *kn, struct pipe *rpipe)
+{
+       struct pipe *wpipe;
+
+       rw_assert_wrlock(rpipe->pipe_lock);
+
+       wpipe = pipe_peer(rpipe);
+
+       if ((rpipe->pipe_state & PIPE_EOF) || wpipe == NULL) {
+               kn->kn_flags |= EV_EOF;
+               if (kn->kn_flags & __EV_POLL)
+                       kn->kn_flags |= __EV_HUP;
+               return (1);
+       }
+
+       return (0);
+}
+
+int
+filt_pipeexcept(struct knote *kn, long hint)
+{
+       struct pipe *rpipe = kn->kn_fp->f_data;
+
+       return (filt_pipeexcept_common(kn, rpipe));
+}
+
+int
+filt_pipeexceptmodify(struct kevent *kev, struct knote *kn)
+{
+       struct pipe *rpipe = kn->kn_fp->f_data;
+       int active;
+
+       rw_enter_write(rpipe->pipe_lock);
+       knote_modify(kev, kn);
+       active = filt_pipeexcept_common(kn, rpipe);
+       rw_exit_write(rpipe->pipe_lock);
+
+       return (active);
+}
+
+int
+filt_pipeexceptprocess(struct knote *kn, struct kevent *kev)
+{
+       struct pipe *rpipe = kn->kn_fp->f_data;
+       int active;
+
+       rw_enter_write(rpipe->pipe_lock);
+       if (kev != NULL && (kn->kn_flags & EV_ONESHOT))
+               active = 1;
+       else
+               active = filt_pipeexcept_common(kn, rpipe);
+       if (active)
+               knote_submit(kn, kev);
+       rw_exit_write(rpipe->pipe_lock);
+
+       return (active);
+}
+
 void
 pipe_init(void)
 {