Diff below switches both poll(2) and select(2) to the kqueue-based
implementation.
In addition it switches libevent(3) to use poll(2) by default for
testing purposes.
I don't have any open bug left with this diff and I'm happily running
GNOME with it. So I'd be happy if you could try to break it and report
back.
Index: lib/libevent/event.c
===================================================================
RCS file: /cvs/src/lib/libevent/event.c,v
retrieving revision 1.41
diff -u -p -r1.41 event.c
--- lib/libevent/event.c 1 May 2019 19:14:25 -0000 1.41
+++ lib/libevent/event.c 23 Oct 2021 09:36:10 -0000
@@ -53,9 +53,9 @@ extern const struct eventop kqops;
/* In order of preference */
static const struct eventop *eventops[] = {
- &kqops,
&pollops,
&selectops,
+ &kqops,
NULL
};
Index: sys/kern/sys_generic.c
===================================================================
RCS file: /cvs/src/sys/kern/sys_generic.c,v
retrieving revision 1.137
diff -u -p -r1.137 sys_generic.c
--- sys/kern/sys_generic.c 15 Oct 2021 06:59:57 -0000 1.137
+++ sys/kern/sys_generic.c 23 Oct 2021 09:14:59 -0000
@@ -55,6 +55,7 @@
#include <sys/time.h>
#include <sys/malloc.h>
#include <sys/poll.h>
+#include <sys/eventvar.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
@@ -66,8 +67,23 @@
#include <uvm/uvm_extern.h>
-int selscan(struct proc *, fd_set *, fd_set *, int, int, register_t *);
-void pollscan(struct proc *, struct pollfd *, u_int, register_t *);
+/*
+ * Debug values:
+ * 1 - print implementation errors, things that should not happen.
+ * 2 - print ppoll(2) information, somewhat verbose
+ * 3 - print pselect(2) and ppoll(2) information, very verbose
+ */
+int kqpoll_debug = 0;
+#define DPRINTFN(v, x...) if (kqpoll_debug > v) { \
+ printf("%s(%d): ", curproc->p_p->ps_comm, curproc->p_tid); \
+ printf(x); \
+}
+
+int pselregister(struct proc *, fd_set *[], fd_set *[], int, int *, int *);
+int pselcollect(struct proc *, struct kevent *, fd_set *[], int *);
+int ppollregister(struct proc *, struct pollfd *, int, int *);
+int ppollcollect(struct proc *, struct kevent *, struct pollfd *, u_int);
+
int pollout(struct pollfd *, struct pollfd *, u_int);
int dopselect(struct proc *, int, fd_set *, fd_set *, fd_set *,
struct timespec *, const sigset_t *, register_t *);
@@ -584,11 +600,10 @@ int
dopselect(struct proc *p, int nd, fd_set *in, fd_set *ou, fd_set *ex,
struct timespec *timeout, const sigset_t *sigmask, register_t *retval)
{
+ struct kqueue_scan_state scan;
fd_mask bits[6];
fd_set *pibits[3], *pobits[3];
- struct timespec elapsed, start, stop;
- uint64_t nsecs;
- int s, ncoll, error = 0;
+ int error, ncollected = 0, nevents = 0;
u_int ni;
if (nd < 0)
@@ -618,6 +633,8 @@ dopselect(struct proc *p, int nd, fd_set
pobits[2] = (fd_set *)&bits[5];
}
+ kqpoll_init();
+
#define getbits(name, x) \
if (name && (error = copyin(name, pibits[x], ni))) \
goto done;
@@ -636,43 +653,61 @@ dopselect(struct proc *p, int nd, fd_set
if (sigmask)
dosigsuspend(p, *sigmask &~ sigcantmask);
-retry:
- ncoll = nselcoll;
- atomic_setbits_int(&p->p_flag, P_SELECT);
- error = selscan(p, pibits[0], pobits[0], nd, ni, retval);
- if (error || *retval)
+ /* Register kqueue events */
+ error = pselregister(p, pibits, pobits, nd, &nevents, &ncollected);
+ if (error != 0)
goto done;
- if (timeout == NULL || timespecisset(timeout)) {
- if (timeout != NULL) {
- getnanouptime(&start);
- nsecs = MIN(TIMESPEC_TO_NSEC(timeout), MAXTSLP);
- } else
- nsecs = INFSLP;
- s = splhigh();
- if ((p->p_flag & P_SELECT) == 0 || nselcoll != ncoll) {
- splx(s);
- goto retry;
- }
- atomic_clearbits_int(&p->p_flag, P_SELECT);
- error = tsleep_nsec(&selwait, PSOCK | PCATCH, "select", nsecs);
- splx(s);
+
+ /*
+ * The poll/select family of syscalls has been designed to
+ * block when file descriptors are not available, even if
+ * there's nothing to wait for.
+ */
+ if (nevents == 0 && ncollected == 0) {
+ uint64_t nsecs = INFSLP;
+
if (timeout != NULL) {
- getnanouptime(&stop);
- timespecsub(&stop, &start, &elapsed);
- timespecsub(timeout, &elapsed, timeout);
- if (timeout->tv_sec < 0)
- timespecclear(timeout);
+ if (!timespecisset(timeout))
+ goto done;
+ nsecs = MAX(1, MIN(TIMESPEC_TO_NSEC(timeout), MAXTSLP));
}
- if (error == 0 || error == EWOULDBLOCK)
- goto retry;
+ error = tsleep_nsec(&p->p_kq, PSOCK | PCATCH, "kqsel", nsecs);
+ /* select is not restarted after signals... */
+ if (error == ERESTART)
+ error = EINTR;
+ if (error == EWOULDBLOCK)
+ error = 0;
+ goto done;
+ }
+
+ /* Collect at most `nevents' possibly waiting in kqueue_scan() */
+ kqueue_scan_setup(&scan, p->p_kq);
+ while (nevents > 0) {
+ struct kevent kev[KQ_NEVENTS];
+ int i, ready, count;
+
+ /* Maximum number of events per iteration */
+ count = MIN(nitems(kev), nevents);
+ ready = kqueue_scan(&scan, count, kev, timeout, p, &error);
+#ifdef KTRACE
+ if (KTRPOINT(p, KTR_STRUCT))
+ ktrevent(p, kev, ready);
+#endif
+ /* Convert back events that are ready. */
+ for (i = 0; i < ready && error == 0; i++)
+ error = pselcollect(p, &kev[i], pobits, &ncollected);
+ /*
+ * Stop if there was an error or if we had enough
+ * space to collect all events that were ready.
+ */
+ if (error || ready < count)
+ break;
+
+ nevents -= ready;
}
+ kqueue_scan_finish(&scan);
+ *retval = ncollected;
done:
- atomic_clearbits_int(&p->p_flag, P_SELECT);
- /* select is not restarted after signals... */
- if (error == ERESTART)
- error = EINTR;
- if (error == EWOULDBLOCK)
- error = 0;
#define putbits(name, x) \
if (name && (error2 = copyout(pobits[x], name, ni))) \
error = error2;
@@ -694,40 +729,112 @@ done:
if (pibits[0] != (fd_set *)&bits[0])
free(pibits[0], M_TEMP, 6 * ni);
+
+ kqueue_purge(p, p->p_kq);
+ p->p_kq_serial += nd;
+
return (error);
}
+/*
+ * Convert fd_set into kqueue events and register them on the
+ * per-thread queue.
+ */
int
-selscan(struct proc *p, fd_set *ibits, fd_set *obits, int nfd, int ni,
- register_t *retval)
+pselregister(struct proc *p, fd_set *pibits[3], fd_set *pobits[3], int nfd,
+ int *nregistered, int *ncollected)
{
- caddr_t cibits = (caddr_t)ibits, cobits = (caddr_t)obits;
- struct filedesc *fdp = p->p_fd;
- int msk, i, j, fd;
+ static const int evf[] = { EVFILT_READ, EVFILT_WRITE, EVFILT_EXCEPT };
+ static const int evff[] = { 0, 0, NOTE_OOB };
+ int msk, i, j, fd, nevents = 0, error = 0;
+ struct kevent kev;
fd_mask bits;
- struct file *fp;
- int n = 0;
- static const int flag[3] = { POLLIN, POLLOUT|POLL_NOHUP, POLLPRI };
for (msk = 0; msk < 3; msk++) {
- fd_set *pibits = (fd_set *)&cibits[msk*ni];
- fd_set *pobits = (fd_set *)&cobits[msk*ni];
-
for (i = 0; i < nfd; i += NFDBITS) {
- bits = pibits->fds_bits[i/NFDBITS];
+ bits = pibits[msk]->fds_bits[i / NFDBITS];
while ((j = ffs(bits)) && (fd = i + --j) < nfd) {
bits &= ~(1 << j);
- if ((fp = fd_getfile(fdp, fd)) == NULL)
- return (EBADF);
- if ((*fp->f_ops->fo_poll)(fp, flag[msk], p)) {
- FD_SET(fd, pobits);
- n++;
+
+ DPRINTFN(2, "select fd %d mask %d serial %lu\n",
+ fd, msk, p->p_kq_serial);
+ EV_SET(&kev, fd, evf[msk],
+ EV_ADD|EV_ENABLE|EV_ONESHOT|__EV_POLL,
+ evff[msk], 0, (void *)(p->p_kq_serial));
+#ifdef KTRACE
+ if (KTRPOINT(p, KTR_STRUCT))
+ ktrevent(p, &kev, 1);
+#endif
+ error = kqueue_register(p->p_kq, &kev, p);
+ switch (error) {
+ case 0:
+ nevents++;
+ /* FALLTHROUGH */
+ case EOPNOTSUPP:/* No underlying kqfilter */
+ case EINVAL: /* Unimplemented filter */
+ case EPERM: /* Specific to FIFO */
+ error = 0;
+ break;
+ case EPIPE: /* Specific to pipes */
+ KASSERT(kev.filter == EVFILT_WRITE);
+ FD_SET(kev.ident, pobits[1]);
+ (*ncollected)++;
+ error = 0;
+ break;
+ case ENXIO: /* Device has been detached */
+ default:
+ goto bad;
}
- FRELE(fp, p);
}
}
}
- *retval = n;
+
+ *nregistered = nevents;
+ return (0);
+bad:
+ DPRINTFN(0, "select fd %u filt %d error %d\n", (int)kev.ident,
+ kev.filter, error);
+ return (error);
+}
+
+/*
+ * Convert given kqueue event into corresponding select(2) bit.
+ */
+int
+pselcollect(struct proc *p, struct kevent *kevp, fd_set *pobits[3],
+ int *ncollected)
+{
+ /* Filter out and lazily delete spurious events */
+ if ((unsigned long)kevp->udata != p->p_kq_serial) {
+ DPRINTFN(0, "select fd %u mismatched serial %lu\n",
+ (int)kevp->ident, p->p_kq_serial);
+ kevp->flags = EV_DISABLE|EV_DELETE;
+ kqueue_register(p->p_kq, kevp, p);
+ return (0);
+ }
+
+ if (kevp->flags & EV_ERROR) {
+ DPRINTFN(2, "select fd %d filt %d error %d\n",
+ (int)kevp->ident, kevp->filter, (int)kevp->data);
+ return (kevp->data);
+ }
+
+ switch (kevp->filter) {
+ case EVFILT_READ:
+ FD_SET(kevp->ident, pobits[0]);
+ break;
+ case EVFILT_WRITE:
+ FD_SET(kevp->ident, pobits[1]);
+ break;
+ case EVFILT_EXCEPT:
+ FD_SET(kevp->ident, pobits[2]);
+ break;
+ default:
+ KASSERT(0);
+ }
+ (*ncollected)++;
+
+ DPRINTFN(2, "select fd %d filt %d\n", (int)kevp->ident, kevp->filter);
return (0);
}
@@ -802,31 +909,134 @@ doselwakeup(struct selinfo *sip)
}
}
-void
-pollscan(struct proc *p, struct pollfd *pl, u_int nfd, register_t *retval)
+int
+ppollregister_evts(struct proc *p, struct kevent *kevp, int nkev,
+ struct pollfd *pl)
{
- struct filedesc *fdp = p->p_fd;
- struct file *fp;
- u_int i;
- int n = 0;
+ int i, error, nevents = 0;
- for (i = 0; i < nfd; i++, pl++) {
- /* Check the file descriptor. */
- if (pl->fd < 0) {
- pl->revents = 0;
- continue;
+ KASSERT(pl->revents == 0);
+
+#ifdef KTRACE
+ if (KTRPOINT(p, KTR_STRUCT))
+ ktrevent(p, kevp, nkev);
+#endif
+ for (i = 0; i < nkev; i++, kevp++) {
+again:
+ error = kqueue_register(p->p_kq, kevp, p);
+ switch (error) {
+ case 0:
+ nevents++;
+ break;
+ case EOPNOTSUPP:/* No underlying kqfilter */
+ case EINVAL: /* Unimplemented filter */
+ break;
+ case EBADF: /* Bad file descriptor */
+ pl->revents |= POLLNVAL;
+ break;
+ case EPERM: /* Specific to FIFO */
+ KASSERT(kevp->filter == EVFILT_WRITE);
+ if (nkev == 1) {
+ /*
+ * If this is the only filter make sure
+ * POLLHUP is passed to userland.
+ */
+ kevp->filter = EVFILT_EXCEPT;
+ goto again;
+ }
+ break;
+ case EPIPE: /* Specific to pipes */
+ KASSERT(kevp->filter == EVFILT_WRITE);
+ pl->revents |= POLLHUP;
+ break;
+ default:
+#ifdef DIAGNOSTIC
+ DPRINTFN(0, "poll err %lu fd %d revents %02x serial"
+ " %lu filt %d ERROR=%d\n",
+ ((unsigned long)kevp->udata - p->p_kq_serial),
+ pl->fd, pl->revents, p->p_kq_serial, kevp->filter,
+ error);
+#endif
+ /* FALLTHROUGH */
+ case ENXIO: /* Device has been detached */
+ pl->revents |= POLLERR;
+ break;
}
- if ((fp = fd_getfile(fdp, pl->fd)) == NULL) {
- pl->revents = POLLNVAL;
- n++;
+ }
+
+ return (nevents);
+}
+
+/*
+ * Convert pollfd into kqueue events and register them on the
+ * per-thread queue.
+ *
+ * Return the number of pollfd that triggered at least one error and aren't
+ * completly monitored. These pollfd should have the correponding error bit
+ * set in `revents'.
+ *
+ * At most 3 events can correspond to a single pollfd.
+ */
+int
+ppollregister(struct proc *p, struct pollfd *pl, int nfds, int *nregistered)
+{
+ int i, nkev, nevt, errcount = 0, forcehup = 0;
+ struct kevent kev[3], *kevp;
+
+ for (i = 0; i < nfds; i++) {
+ pl[i].events &= ~POLL_NOHUP;
+ pl[i].revents = 0;
+
+ if (pl[i].fd < 0)
continue;
+
+ if (pl[i].events == 0)
+ forcehup = 1;
+
+ DPRINTFN(1, "poll set %d/%d fd %d events %02x serial %lu\n",
+ i+1, nfds, pl[i].fd, pl[i].events, p->p_kq_serial);
+
+ nevt = 0;
+ nkev = 0;
+ kevp = kev;
+ if (pl[i].events & (POLLIN | POLLRDNORM)) {
+ EV_SET(kevp, pl[i].fd, EVFILT_READ,
+ EV_ADD|EV_ENABLE|EV_ONESHOT|__EV_POLL, 0, 0,
+ (void *)(p->p_kq_serial + i));
+ nkev++;
+ kevp++;
+ }
+ if (pl[i].events & (POLLOUT | POLLWRNORM)) {
+ EV_SET(kevp, pl[i].fd, EVFILT_WRITE,
+ EV_ADD|EV_ENABLE|EV_ONESHOT|__EV_POLL, 0, 0,
+ (void *)(p->p_kq_serial + i));
+ nkev++;
+ kevp++;
+ }
+ if ((pl[i].events & (POLLPRI | POLLRDBAND)) || forcehup) {
+ int evff = forcehup ? 0 : NOTE_OOB;
+
+ EV_SET(kevp, pl[i].fd, EVFILT_EXCEPT,
+ EV_ADD|EV_ENABLE|EV_ONESHOT|__EV_POLL, evff, 0,
+ (void *)(p->p_kq_serial + i));
+ nkev++;
+ kevp++;
}
- pl->revents = (*fp->f_ops->fo_poll)(fp, pl->events, p);
- FRELE(fp, p);
- if (pl->revents != 0)
- n++;
+
+ if (nkev == 0)
+ continue;
+
+ nevt = ppollregister_evts(p, kev, nkev, &pl[i]);
+ if (nevt == 0 && !forcehup)
+ errcount++;
+ *nregistered += nevt;
}
- *retval = n;
+
+#if DIAGNOSTIC
+ DPRINTFN(1, "poll registered = %d, errors = %d\n", *nregistered,
+ errcount);
+#endif
+ return (errcount);
}
/*
@@ -916,11 +1126,10 @@ int
doppoll(struct proc *p, struct pollfd *fds, u_int nfds,
struct timespec *timeout, const sigset_t *sigmask, register_t *retval)
{
- size_t sz;
+ struct kqueue_scan_state scan;
struct pollfd pfds[4], *pl = pfds;
- struct timespec elapsed, start, stop;
- uint64_t nsecs;
- int ncoll, i, s, error;
+ int error, nevents = 0;
+ size_t sz;
/* Standards say no more than MAX_OPEN; this is possibly better. */
if (nfds > min((int)lim_cur(RLIMIT_NOFILE), maxfiles))
@@ -934,58 +1143,75 @@ doppoll(struct proc *p, struct pollfd *f
return (EINVAL);
}
+ kqpoll_init();
+
sz = nfds * sizeof(*pl);
if ((error = copyin(fds, pl, sz)) != 0)
goto bad;
- for (i = 0; i < nfds; i++) {
- pl[i].events &= ~POLL_NOHUP;
- pl[i].revents = 0;
- }
-
if (sigmask)
dosigsuspend(p, *sigmask &~ sigcantmask);
-retry:
- ncoll = nselcoll;
- atomic_setbits_int(&p->p_flag, P_SELECT);
- pollscan(p, pl, nfds, retval);
- if (*retval)
- goto done;
- if (timeout == NULL || timespecisset(timeout)) {
- if (timeout != NULL) {
- getnanouptime(&start);
- nsecs = MIN(TIMESPEC_TO_NSEC(timeout), MAXTSLP);
- } else
- nsecs = INFSLP;
- s = splhigh();
- if ((p->p_flag & P_SELECT) == 0 || nselcoll != ncoll) {
- splx(s);
- goto retry;
- }
- atomic_clearbits_int(&p->p_flag, P_SELECT);
- error = tsleep_nsec(&selwait, PSOCK | PCATCH, "poll", nsecs);
- splx(s);
+ /* Register kqueue events */
+ *retval = ppollregister(p, pl, nfds, &nevents);
+
+ /*
+ * The poll/select family of syscalls has been designed to
+ * block when file descriptors are not available, even if
+ * there's nothing to wait for.
+ */
+ if (nevents == 0) {
+ uint64_t nsecs = INFSLP;
+
if (timeout != NULL) {
- getnanouptime(&stop);
- timespecsub(&stop, &start, &elapsed);
- timespecsub(timeout, &elapsed, timeout);
- if (timeout->tv_sec < 0)
- timespecclear(timeout);
+ if (!timespecisset(timeout))
+ goto done;
+ nsecs = MAX(1, MIN(TIMESPEC_TO_NSEC(timeout), MAXTSLP));
}
- if (error == 0 || error == EWOULDBLOCK)
- goto retry;
+
+ error = tsleep_nsec(&p->p_kq, PSOCK | PCATCH, "kqpoll", nsecs);
+ if (error == ERESTART)
+ error = EINTR;
+ if (error == EWOULDBLOCK)
+ error = 0;
+ goto done;
}
+ /* Collect at most `nevents' possibly waiting in kqueue_scan() */
+ kqueue_scan_setup(&scan, p->p_kq);
+ while (nevents > 0) {
+ struct kevent kev[KQ_NEVENTS];
+ int i, ready, count;
+
+ /* Maxium number of events per iteration */
+ count = MIN(nitems(kev), nevents);
+ ready = kqueue_scan(&scan, count, kev, timeout, p, &error);
+#ifdef KTRACE
+ if (KTRPOINT(p, KTR_STRUCT))
+ ktrevent(p, kev, ready);
+#endif
+ /* Convert back events that are ready. */
+ for (i = 0; i < ready; i++)
+ *retval += ppollcollect(p, &kev[i], pl, nfds);
+
+ /*
+ * Stop if there was an error or if we had enough
+ * place to collect all events that were ready.
+ */
+ if (error || ready < count)
+ break;
+
+ nevents -= ready;
+ }
+ kqueue_scan_finish(&scan);
done:
- atomic_clearbits_int(&p->p_flag, P_SELECT);
/*
* NOTE: poll(2) is not restarted after a signal and EWOULDBLOCK is
* ignored (since the whole point is to see what would block).
*/
switch (error) {
- case ERESTART:
+ case EINTR:
error = pollout(pl, fds, nfds);
if (error == 0)
error = EINTR;
@@ -1002,7 +1228,95 @@ done:
bad:
if (pl != pfds)
free(pl, M_TEMP, sz);
+
+ kqueue_purge(p, p->p_kq);
+ p->p_kq_serial += nfds;
+
return (error);
+}
+
+/*
+ * Convert given kqueue event into corresponding poll(2) revents bit.
+ */
+int
+ppollcollect(struct proc *p, struct kevent *kevp, struct pollfd *pl, u_int
nfds)
+{
+ int already_seen;
+ unsigned long i;
+
+ /* Extract poll array index */
+ i = (unsigned long)kevp->udata - p->p_kq_serial;
+
+#ifdef DIAGNOSTIC
+ /*
+ * Lazily delete spurious events.
+ *
+ * This should not happen as long as kqueue_purge() is called
+ * at the end of every syscall. It migh be interesting to do
+ * like DragonFlyBSD and not always allocated a new knote in
+ * kqueue_register() with that lazy removal makes sense.
+ */
+ if (i >= nfds) {
+ DPRINTFN(0, "poll get out of range udata %lu vs serial %lu\n",
+ (unsigned long)kevp->udata, p->p_kq_serial);
+ kevp->flags = EV_DISABLE|EV_DELETE;
+ kqueue_register(p->p_kq, kevp, p);
+ return (0);
+ }
+ if ((int)kevp->ident != pl[i].fd) {
+ DPRINTFN(0, "poll get %lu/%d mismatch fd %u!=%d serial %lu\n",
+ i+1, nfds, (int)kevp->ident, pl[i].fd, p->p_kq_serial);
+ return (0);
+ }
+#endif
+
+ /*
+ * A given descriptor may already have generated an error
+ * against another filter during kqueue_register().
+ *
+ * Make sure to set the appropriate flags but do not
+ * increment `*retval' more than once.
+ */
+ already_seen = (pl[i].revents != 0);
+
+ switch (kevp->filter) {
+ case EVFILT_READ:
+ if (kevp->flags & __EV_HUP)
+ pl[i].revents |= POLLHUP;
+ if (pl[i].events & (POLLIN | POLLRDNORM))
+ pl[i].revents |= pl[i].events & (POLLIN | POLLRDNORM);
+ break;
+ case EVFILT_WRITE:
+ /* NOTE: POLLHUP and POLLOUT/POLLWRNORM are mutually exclusive*/
+ if (kevp->flags & __EV_HUP) {
+ pl[i].revents |= POLLHUP;
+ } else if (pl[i].events & (POLLOUT | POLLWRNORM)) {
+ pl[i].revents |= pl[i].events & (POLLOUT | POLLWRNORM);
+ }
+ break;
+ case EVFILT_EXCEPT:
+ if (kevp->flags & __EV_HUP) {
+#if 1
+ if (pl[i].events != 0 && pl[i].events != POLLOUT)
+ DPRINTFN(0, "weird events %x\n", pl[i].events);
+#endif
+ pl[i].revents |= POLLHUP;
+ break;
+ }
+ if (pl[i].events & (POLLPRI | POLLRDBAND))
+ pl[i].revents |= pl[i].events & (POLLPRI | POLLRDBAND);
+ break;
+ default:
+ KASSERT(0);
+ }
+
+ DPRINTFN(1, "poll get %lu/%d fd %d revents %02x serial %lu filt %d\n",
+ i+1, nfds, pl[i].fd, pl[i].revents, (unsigned long)kevp->udata,
+ kevp->filter);
+ if (!already_seen && (pl[i].revents != 0))
+ return (1);
+
+ return (0);
}
/*
Index: sys/miscfs/fifofs/fifo_vnops.c
===================================================================
RCS file: /cvs/src/sys/miscfs/fifofs/fifo_vnops.c,v
retrieving revision 1.83
diff -u -p -r1.83 fifo_vnops.c
--- sys/miscfs/fifofs/fifo_vnops.c 22 Oct 2021 15:11:32 -0000 1.83
+++ sys/miscfs/fifofs/fifo_vnops.c 23 Oct 2021 09:14:59 -0000
@@ -529,8 +529,12 @@ fifo_kqfilter(void *v)
sb = &so->so_rcv;
break;
case EVFILT_WRITE:
- if (!(ap->a_fflag & FWRITE))
+ if (!(ap->a_fflag & FWRITE)) {
+ /* Tell uper layer to ask for POLLUP only */
+ if (ap->a_kn->kn_flags & __EV_POLL)
+ return (EPERM);
return (EINVAL);
+ }
ap->a_kn->kn_fop = &fifowrite_filtops;
so = fip->fi_writesock;
sb = &so->so_snd;
