Corner cases fixed mentioned in pr

extent.c

@@ -17,7 +17,7 @@ uint32_t simplefs_ext_search(struct simplefs_file_ei_block *index,
      */
     uint32_t start = 0;
     uint32_t end = SIMPLEFS_MAX_EXTENTS - 1;
-    uint32_t boundary = -1;
+    uint32_t boundary;
     uint32_t end_block;
     uint32_t end_len;
 
@@ -30,8 +30,16 @@ uint32_t simplefs_ext_search(struct simplefs_file_ei_block *index,
         }
     }
 
-    if (end != SIMPLEFS_MAX_EXTENTS - 1 || index->extents[end].ee_start == 0) {
+    if (index->extents[end].ee_start == 0) {
         boundary = end;
+    } else {
+        /* File index full */
+        boundary = end + 1;
+    }
+
+    if (boundary == 0) {
+        /* No used file index */
+        return boundary;
     }
 
     /* try finding target block using binary search */
@@ -52,12 +60,16 @@ uint32_t simplefs_ext_search(struct simplefs_file_ei_block *index,
         }
     }
 
-    /* check that end directs to valid block. */
+    /* return 'end' if it directs to valid block
+     * return 'boundary' if index is not found
+     * and eiblock has remaining space */
     end_block = index->extents[end].ee_block;
     end_len = index->extents[end].ee_len;
-
     if (iblock >= end_block && iblock < end_len) {
         return end;
+    } else if (boundary < SIMPLEFS_MAX_EXTENTS) {
+        return boundary;
     }
-    return boundary;
+
+    return -1;
 }