Fix vnode locking bugs in the nullfs.

Add correct support for v_object management, so mmap() operation should
work properly.
Add support for extattrctl() routine (submitted by semenu).

At this point nullfs can be considered as functional and much more stable.
In fact, it should behave as a "hard" "symlink" to underlying filesystem.

Reviewed in general by:		mckusick, dillon
Parts of logic obtained from:	NetBSD

1 files changed, 29 insertions, 9 deletions

diff --git a/sys/fs/nullfs/null_subr.c b/sys/fs/nullfs/null_subr.c
index 3671f0a..efb1357 100644
--- a/sys/fs/nullfs/null_subr.c
+++ b/sys/fs/nullfs/null_subr.c
@@ -99,6 +99,7 @@ nullfs_uninit(vfsp)
 
 /*
  * Return a VREF'ed alias for lower vnode if already exists, else 0.
+ * Lower vnode should be locked on entry and will be left locked on exit.
  */
 static struct vnode *
 null_node_find(mp, lowervp)
@@ -128,10 +129,15 @@ loop:
 			 * stuff, but we don't want to lock
 			 * the lower node.
 			 */
-			if (vget(vp, 0, p)) {
+			if (vget(vp, LK_EXCLUSIVE | LK_CANRECURSE, p)) {
 				printf ("null_node_find: vget failed.\n");
 				goto loop;
 			};
+			/*
+			 * Now we got both vnodes locked, so release the
+			 * lower one.
+			 */
+			VOP_UNLOCK(lowervp, 0, p);
 			return (vp);
 		}
 	}
@@ -184,14 +190,30 @@ null_node_alloc(mp, lowervp, vpp)
 	 */
 	othervp = null_node_find(mp, lowervp);
 	if (othervp) {
+		vp->v_data = NULL;
 		FREE(xp, M_NULLFSNODE);
 		vp->v_type = VBAD;	/* node is discarded */
-		vp->v_usecount = 0;	/* XXX */
+		vrele(vp);
 		*vpp = othervp;
 		return 0;
 	};
+
+	/*
+	 * From NetBSD:
+	 * Now lock the new node. We rely on the fact that we were passed
+	 * a locked vnode. If the lower node is exporting a struct lock
+	 * (v_vnlock != NULL) then we just set the upper v_vnlock to the
+	 * lower one, and both are now locked. If the lower node is exporting
+	 * NULL, then we copy that up and manually lock the new vnode.
+	 */
+
 	lockmgr(&null_hashlock, LK_EXCLUSIVE, NULL, p);
-	VREF(lowervp);   /* Extra VREF will be vrele'd in null_node_create */
+	vp->v_vnlock = lowervp->v_vnlock;
+	error = VOP_LOCK(vp, LK_EXCLUSIVE | LK_THISLAYER, p);
+	if (error)
+		panic("null_node_alloc: can't lock new vnode\n");
+
+	VREF(lowervp);
 	hd = NULL_NHASH(lowervp);
 	LIST_INSERT_HEAD(hd, xp, null_hash);
 	lockmgr(&null_hashlock, LK_RELEASE, NULL, p);
@@ -200,9 +222,9 @@ null_node_alloc(mp, lowervp, vpp)
 
 
 /*
- * Try to find an existing null_node vnode refering
- * to it, otherwise make a new null_node vnode which
- * contains a reference to the lower vnode.
+ * Try to find an existing null_node vnode refering to the given underlying
+ * vnode (which should be locked). If no vnode found, create a new null_node
+ * vnode which contains a reference to the lower vnode.
  */
 int
 null_node_create(mp, lowervp, newvpp)
@@ -218,10 +240,10 @@ null_node_create(mp, lowervp, newvpp)
 		 * null_node_find has taken another reference
 		 * to the alias vnode.
 		 */
+		 vrele(lowervp);
 #ifdef NULLFS_DEBUG
 		vprint("null_node_create: exists", aliasvp);
 #endif
-		/* VREF(aliasvp); --- done in null_node_find */
 	} else {
 		int error;
 
@@ -242,8 +264,6 @@ null_node_create(mp, lowervp, newvpp)
 		 */
 	}
 
-	vrele(lowervp);
-
 #ifdef DIAGNOSTIC
 	if (lowervp->v_usecount < 1) {
 		/* Should never happen... */