Add support for poll(2) on files. vop_nopoll() now returns POLLNVAL

if one of the new poll types is requested; hopefully this will not break
any existing code.  (This is done so that programs have a dependable
way of determining whether a filesystem supports the extended poll types
or not.)

The new poll types added are:

	POLLWRITE - file contents may have been modified
	POLLNLINK - file was linked, unlinked, or renamed
	POLLATTRIB - file's attributes may have been changed
	POLLEXTEND - file was extended

Note that the internal operation of poll() means that it is impossible
for two processes to reliably poll for the same event (this could
be fixed but may not be worth it), so it is not possible to rewrite
`tail -f' to use poll at this time.

1 files changed, 20 insertions, 5 deletions

diff --git a/sys/miscfs/deadfs/dead_vnops.c b/sys/miscfs/deadfs/dead_vnops.c
index 99f58a6..fb11c2a 100644
--- a/sys/miscfs/deadfs/dead_vnops.c
+++ b/sys/miscfs/deadfs/dead_vnops.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)dead_vnops.c	8.1 (Berkeley) 6/10/93
- * $Id: dead_vnops.c,v 1.21 1997/10/26 20:55:10 phk Exp $
+ * $Id: dead_vnops.c,v 1.22 1997/12/05 19:55:41 bde Exp $
  */
 
 #include <sys/param.h>
@@ -40,20 +40,22 @@
 #include <sys/lock.h>
 #include <sys/vnode.h>
 #include <sys/buf.h>
+#include <sys/poll.h>
 
 static int	chkvnlock __P((struct vnode *));
 /*
  * Prototypes for dead operations on vnodes.
  */
 static int	dead_badop __P((void));
+static int	dead_bmap __P((struct vop_bmap_args *));
+static int	dead_ioctl __P((struct vop_ioctl_args *));
+static int	dead_lock __P((struct vop_lock_args *));
 static int	dead_lookup __P((struct vop_lookup_args *));
 static int	dead_open __P((struct vop_open_args *));
+static int	dead_poll __P((struct vop_poll_args *));
+static int	dead_print __P((struct vop_print_args *));
 static int	dead_read __P((struct vop_read_args *));
 static int	dead_write __P((struct vop_write_args *));
-static int	dead_ioctl __P((struct vop_ioctl_args *));
-static int	dead_lock __P((struct vop_lock_args *));
-static int	dead_bmap __P((struct vop_bmap_args *));
-static int	dead_print __P((struct vop_print_args *));
 
 vop_t **dead_vnodeop_p;
 static struct vnodeopv_entry_desc dead_vnodeop_entries[] = {
@@ -73,6 +75,7 @@ static struct vnodeopv_entry_desc dead_vnodeop_entries[] = {
 	{ &vop_mmap_desc,		(vop_t *) dead_badop },
 	{ &vop_open_desc,		(vop_t *) dead_open },
 	{ &vop_pathconf_desc,		(vop_t *) vop_ebadf },	/* per pathconf(2) */
+	{ &vop_poll_desc,		(vop_t *) dead_poll },
 	{ &vop_print_desc,		(vop_t *) dead_print },
 	{ &vop_read_desc,		(vop_t *) dead_read },
 	{ &vop_readdir_desc,		(vop_t *) vop_ebadf },
@@ -288,3 +291,15 @@ chkvnlock(vp)
 	}
 	return (locked);
 }
+
+/*
+ * Trivial poll routine that always returns POLLHUP.
+ * This is necessary so that a process which is polling a file
+ * gets notified when that file is revoke()d.
+ */
+static int
+dead_poll(ap)
+	struct vop_poll_args *ap;
+{
+	return (POLLHUP);
+}