On 20/05/20(Wed) 14:22, Martin Pieuchot wrote:
> On 20/05/20(Wed) 12:28, Mark Kettenis wrote:
> > > Date: Wed, 20 May 2020 11:42:32 +0200
> > > From: Martin Pieuchot <[email protected]>
> > >
> > > Diff below fixes an incoherency between poll(2) and kqueue(2) when it
> > > comes to non-character devices. It makes spec_kqfilter() behaves like
> > > spec_poll(): returns "true" when applied to any non-character device.
> > >
> > > ok?
> >
> > That is a change in behaviour. What do other BSDs do in this case?
>
> By reading code I figured out that:
> - NetBSD only calls the kqfilter handler for character devices and
> returns EOPNOTSUPP otherwise.
>
> - FreeBSD doesn't allow opening block devices in devfs_open(), so
> only character devices seem to support poll(2) and kqueue(2).
>
> - I couldn't find a difference between block and character devices
> handling in DragonFlyBSD, it seems that the underlying kqfilter
> handler is always called.
>
> > I think the new behaviour makes sense, but it could reveal some nasty
> > bugs in cases where code accidantily uses kqueue(2) with a file
> > descriptor for a block device.
>
> The alternative I could think of was changing the existing poll handler
> to do selfalse() instead of seltrue(). However this makes it very hard
> to figure out a regression. On the other hand, assuming that a block
> device is always ready to be read via kqueue(2) seems to have a low
> impact.
Updated diff that considers the new EV_OLDAPI flag and fallbacks to
seltrue_kqfilter() if it is set.
This flag is kernel-only an intended to be set by the new poll(2) and
select(2) implementations. This way kevent(2) keeps its current
behavior.
While here change cttykqfilter() in the same way.
ok?
Index: kern/spec_vnops.c
===================================================================
RCS file: /cvs/src/sys/kern/spec_vnops.c,v
retrieving revision 1.100
diff -u -p -r1.100 spec_vnops.c
--- kern/spec_vnops.c 20 Jan 2020 23:21:55 -0000 1.100
+++ kern/spec_vnops.c 9 Jun 2020 08:57:14 -0000
@@ -386,11 +386,9 @@ spec_poll(void *v)
dev_t dev;
switch (ap->a_vp->v_type) {
-
default:
return (ap->a_events &
(POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM));
-
case VCHR:
dev = ap->a_vp->v_rdev;
return (*cdevsw[major(dev)].d_poll)(dev, ap->a_events, ap->a_p);
@@ -400,12 +398,19 @@ int
spec_kqfilter(void *v)
{
struct vop_kqfilter_args *ap = v;
-
dev_t dev;
dev = ap->a_vp->v_rdev;
- if (cdevsw[major(dev)].d_kqfilter)
- return (*cdevsw[major(dev)].d_kqfilter)(dev, ap->a_kn);
+
+ switch (ap->a_vp->v_type) {
+ default:
+ if (ap->a_kn->kn_flags & EV_OLDAPI)
+ return seltrue_kqfilter(dev, ap->a_kn);
+ break;
+ case VCHR:
+ if (cdevsw[major(dev)].d_kqfilter)
+ return (*cdevsw[major(dev)].d_kqfilter)(dev, ap->a_kn);
+ }
return (EOPNOTSUPP);
}
Index: kern/tty_tty.c
===================================================================
RCS file: /cvs/src/sys/kern/tty_tty.c,v
retrieving revision 1.25
diff -u -p -r1.25 tty_tty.c
--- kern/tty_tty.c 8 Apr 2020 08:07:51 -0000 1.25
+++ kern/tty_tty.c 9 Jun 2020 08:57:55 -0000
@@ -158,7 +158,10 @@ cttykqfilter(dev_t dev, struct knote *kn
{
struct vnode *ttyvp = cttyvp(curproc);
- if (ttyvp == NULL)
+ if (ttyvp == NULL) {
+ if (kn->kn_flags & EV_OLDAPI)
+ return (seltrue_kqfilter(dev, kn));
return (ENXIO);
+ }
return (VOP_KQFILTER(ttyvp, FREAD|FWRITE, kn));
}
