Add asserts to check for file descriptor ring corruption.

src/backend/storage/file/fd.c

@@ -6,7 +6,7 @@
  * Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *    $Id: fd.c,v 1.10 1996/12/04 03:05:58 bryanh Exp $
+ *    $Id: fd.c,v 1.11 1996/12/27 22:57:51 bryanh Exp $
  *
  * NOTES:
  *
@@ -169,7 +169,9 @@ static char Sep_char = '\\';
  * AssertLruRoom   - make sure that there is a free fd.
  *
  * the Last Recently Used ring is a doubly linked list that begins and
- * ends on element zero.
+ * ends on element zero.  Element zero is special -- it doesn't represent
+ * a file and its "fd" field always == VFD_CLOSED.  Element zero is just an
+ * anchor that shows us the beginning/end of the ring.
  *
  * example:
  *
@@ -373,6 +375,10 @@ AssertLruRoom()
                  FreeFd));
     
     if (FreeFd <= 0 || nfile >= MAXFILES) {
+        /* We supposedly are using more vfds than we want to be.  First
+           assert that there is at least one used vfd in the ring. 
+           */
+        Assert(VfdCache[0].lruMoreRecently ! 0);
         LruDelete(VfdCache[0].lruMoreRecently);
     }
 }
@@ -521,6 +527,7 @@ FileAccess(File file)
 void
 FileInvalidate(File file)
 {
+    Assert(file > 0);
     if (!FileIsNotOpen(file)) {
         LruDelete(file);
     }
@@ -879,7 +886,8 @@ void
 closeAllVfds()
 {
     int i;
-    for (i=0; i<SizeVfdCache; i++) {
+    Assert (FileIsNotOpen(0));  /* Make sure ring not corrupted */
+    for (i=1; i<SizeVfdCache; i++) {
         if (!FileIsNotOpen(i))
             LruDelete(i);
     }