bug: fifo kqfilter & FREAD|FWRITE

[Martin Pieuchot]

fifo_poll() honors FREAD and FWRITE.  It doesn't return events
incompatible with the open flags.  Diff below makes the kqfilters
behave like that as well.

ok?

Index: kern/tty_tty.c
===================================================================
RCS file: /cvs/src/sys/kern/tty_tty.c,v
retrieving revision 1.24
diff -u -p -r1.24 tty_tty.c
--- kern/tty_tty.c      2 May 2018 02:24:56 -0000       1.24
+++ kern/tty_tty.c      7 Apr 2020 10:36:08 -0000
@@ -160,5 +160,5 @@ cttykqfilter(dev_t dev, struct knote *kn
 
        if (ttyvp == NULL)
                return (ENXIO);
-       return (VOP_KQFILTER(ttyvp, kn));
+       return (VOP_KQFILTER(ttyvp, FREAD|FWRITE, kn));
 }
Index: kern/vfs_vnops.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_vnops.c,v
retrieving revision 1.113
diff -u -p -r1.113 vfs_vnops.c
--- kern/vfs_vnops.c    22 Feb 2020 11:58:29 -0000      1.113
+++ kern/vfs_vnops.c    7 Apr 2020 10:36:08 -0000
@@ -619,7 +619,7 @@ vn_closefile(struct file *fp, struct pro
 int
 vn_kqfilter(struct file *fp, struct knote *kn)
 {
-       return (VOP_KQFILTER(fp->f_data, kn));
+       return (VOP_KQFILTER(fp->f_data, fp->f_flag, kn));
 }
 
 int
Index: kern/vfs_vops.c
===================================================================
RCS file: /cvs/src/sys/kern/vfs_vops.c,v
retrieving revision 1.27
diff -u -p -r1.27 vfs_vops.c
--- kern/vfs_vops.c     31 Mar 2020 06:54:05 -0000      1.27
+++ kern/vfs_vops.c     7 Apr 2020 10:36:08 -0000
@@ -307,10 +307,11 @@ VOP_POLL(struct vnode *vp, int fflag, in
 }
 
 int
-VOP_KQFILTER(struct vnode *vp, struct knote *kn)
+VOP_KQFILTER(struct vnode *vp, int fflag, struct knote *kn)
 {
        struct vop_kqfilter_args a;
        a.a_vp = vp;
+       a.a_fflag = fflag;
        a.a_kn = kn;
 
        if (vp->v_op->vop_kqfilter == NULL)
Index: sys/vnode.h
===================================================================
RCS file: /cvs/src/sys/sys/vnode.h,v
retrieving revision 1.155
diff -u -p -r1.155 vnode.h
--- sys/vnode.h 20 Jan 2020 23:21:56 -0000      1.155
+++ sys/vnode.h 7 Apr 2020 10:36:08 -0000
@@ -412,9 +412,10 @@ int VOP_POLL(struct vnode *, int, int, s
 
 struct vop_kqfilter_args {
        struct vnode *a_vp;
+       int a_fflag;
        struct knote *a_kn;
 };
-int VOP_KQFILTER(struct vnode *, struct knote *);
+int VOP_KQFILTER(struct vnode *, int, struct knote *);
 
 struct vop_revoke_args {
        struct vnode *a_vp;
Index: miscfs/fifofs/fifo_vnops.c
===================================================================
RCS file: /cvs/src/sys/miscfs/fifofs/fifo_vnops.c,v
retrieving revision 1.73
diff -u -p -r1.73 fifo_vnops.c
--- miscfs/fifofs/fifo_vnops.c  20 Feb 2020 16:56:52 -0000      1.73
+++ miscfs/fifofs/fifo_vnops.c  7 Apr 2020 10:37:42 -0000
@@ -512,10 +512,14 @@ fifo_kqfilter(void *v)
 
        switch (ap->a_kn->kn_filter) {
        case EVFILT_READ:
+               if (!(ap->a_fflag & FREAD))
+                       return (EINVAL);
                ap->a_kn->kn_fop = &fiforead_filtops;
                sb = &so->so_rcv;
                break;
        case EVFILT_WRITE:
+               if (!(ap->a_fflag & FWRITE))
+                       return (EINVAL);
                ap->a_kn->kn_fop = &fifowrite_filtops;
                sb = &so->so_snd;
                break;