fifo: minor comment and assert improvements.

In particular, replace a note that reload through vget() is obsoleted,
with explanation why this code is required.

Reviewed by:	chs, mckusick
Tested by:	pho
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation

sys/kern/vfs_syscalls.c

@@ -1183,7 +1183,8 @@ kern_openat(struct thread *td, int fd, const char *path, enum uio_seg pathseg,
 	 * vnode operations here.
 	 */
 	if (fp->f_ops == &badfileops) {
-		KASSERT(vp->v_type != VFIFO, ("Unexpected fifo."));
+		KASSERT(vp->v_type != VFIFO,
+		    ("Unexpected fifo fp %p vp %p", fp, vp));
 		finit_vnode(fp, flags, NULL, &vnops);
 	}
 

sys/ufs/ufs/ufs_vnops.c

@@ -252,9 +252,10 @@ ufs_mknod(ap)
 		DIP_SET(ip, i_rdev, vap->va_rdev);
 	}
 	/*
-	 * Remove inode, then reload it through VFS_VGET so it is
-	 * checked to see if it is an alias of an existing entry in
-	 * the inode cache.  XXX I don't believe this is necessary now.
+	 * Remove inode, then reload it through VFS_VGET().  This is
+	 * needed to do further inode initialization, for instance
+	 * fifo, which was too early for VFS_VGET() done as part of
+	 * UFS_VALLOC().
 	 */
 	(*vpp)->v_type = VNON;
 	ino = ip->i_number;	/* Save this before vgone() invalidates ip. */