diff --git a/src/libisofs.h b/src/libisofs.h
index 6a1b867..ea4e3b7 100644
--- a/src/libisofs.h
+++ b/src/libisofs.h
@@ -68,6 +68,27 @@ enum eltorito_boot_media_type {
     ELTORITO_NO_EMUL
 };
 
+/**
+ * Replace mode used when addding a node to a file.
+ * TODO comment
+ */
+enum iso_replace_mode {
+    /**
+     * Never replace an existing node, and instead fail with 
+     * ISO_NODE_NAME_NOT_UNIQUE.
+     */
+    ISO_REPLACE_NEVER,
+    /**
+     * Always replace the old node with the new.
+     */
+    ISO_REPLACE_ALWAYS
+    /*
+     * TODO #00006 define more values
+     *  -to replace only if both are the same kind of file
+     *  -if both are dirs, add contents (and what to do with conflicts?)
+     */
+};
+
 /**
  * Holds the options for the image generation.
  */
@@ -770,11 +791,6 @@ void iso_node_set_hidden(IsoNode *node, int hide_attrs);
  * @param replace
  *     if the dir already contains a node with the same name, whether to
  *     replace or not the old node with this. 
- *      - 0 not replace (will fail with ISO_NODE_NAME_NOT_UNIQUE)
- *      - 1 replace 
- *      TODO #00006 define more values
- *          to replace only if both are the same kind of file
- *          if both are dirs, add contents (and what to do with conflicts?)
  * @return
  *     number of nodes in dir if succes, < 0 otherwise
  *     Possible errors:
@@ -783,7 +799,8 @@ void iso_node_set_hidden(IsoNode *node, int hide_attrs);
  *         ISO_NODE_NAME_NOT_UNIQUE, a node with same name already exists
  *         ISO_WRONG_ARG_VALUE, if child == dir, or replace != (0,1)
  */
-int iso_dir_add_node(IsoDir *dir, IsoNode *child, int replace);
+int iso_dir_add_node(IsoDir *dir, IsoNode *child, 
+                     enum iso_replace_mode replace);
 
 /**
  * Locate a node inside a given dir.
@@ -1251,7 +1268,7 @@ int iso_image_obtain_msgs(IsoImage *image, char *minimum_severity,
 
 /**
  * Return the messenger object handle used by the given image. This handle
- * may be used by related libraries to replace their own compatible
+ * may be used by related libraries to  their own compatible
  * messenger objects and thus to direct their messages to the libisofs
  * message queue. See also: libburn, API function burn_set_messenger().
  * 
diff --git a/src/node.c b/src/node.c
index 0628f49..1d19585 100644
--- a/src/node.c
+++ b/src/node.c
@@ -259,10 +259,14 @@ void iso_node_set_hidden(IsoNode *node, int hide_attrs)
  *     to other dir, and that the node name is unique inside the child.
  *     Otherwise this function will return a failure, and the child won't be
  *     inserted.
+ * @param replace
+ *     if the dir already contains a node with the same name, whether to
+ *     replace or not the old node with this. 
  * @return
  *     number of nodes in dir if succes, < 0 otherwise
  */
-int iso_dir_add_node(IsoDir *dir, IsoNode *child, int replace)
+int iso_dir_add_node(IsoDir *dir, IsoNode *child, 
+                     enum iso_replace_mode replace)
 {
     IsoNode **pos;
 
@@ -281,32 +285,8 @@ int iso_dir_add_node(IsoDir *dir, IsoNode *child, int replace)
         return ISO_NODE_ALREADY_ADDED;
     }
 
-    pos = &(dir->children);
-    while (*pos != NULL && strcmp((*pos)->name, child->name) < 0) {
-        pos = &((*pos)->next);
-    }
-    if (*pos != NULL && !strcmp((*pos)->name, child->name)) {
-        /* a node with same name already exists */
-        if (replace == 0) {
-            return ISO_NODE_NAME_NOT_UNIQUE;
-        } else if (replace == 1) {
-            child->next = (*pos)->next;
-            (*pos)->parent = NULL;
-            (*pos)->next = NULL;
-            iso_node_unref(*pos);
-            *pos = child;
-            child->parent = dir;
-            return dir->nchildren;
-        } else {
-            return ISO_WRONG_ARG_VALUE;
-        }
-    }
-
-    child->next = *pos;
-    *pos = child;
-    child->parent = dir;
-
-    return ++dir->nchildren;
+    iso_dir_find(dir, child->name, &pos);
+    return iso_dir_insert(dir, child, pos, replace);
 }
 
 /**
@@ -328,17 +308,14 @@ int iso_dir_add_node(IsoDir *dir, IsoNode *child, int replace)
  */
 int iso_dir_get_node(IsoDir *dir, const char *name, IsoNode **node)
 {
-    IsoNode *pos;
+    int ret;
+    IsoNode **pos;
     if (dir == NULL || name == NULL) {
         return ISO_NULL_POINTER;
     }
 
-    pos = dir->children;
-    while (pos != NULL && strcmp(pos->name, name) < 0) {
-        pos = pos->next;
-    }
-
-    if (pos == NULL || strcmp(pos->name, name)) {
+    ret = iso_dir_exists(dir, name, &pos);
+    if (ret == 0) {
         if (node) {
             *node = NULL;
         }
@@ -346,7 +323,7 @@ int iso_dir_get_node(IsoDir *dir, const char *name, IsoNode **node)
     }
 
     if (node) {
-        *node = pos;
+        *node = *pos;
     }
     return 1;
 }
@@ -686,6 +663,53 @@ int iso_node_is_valid_link_dest(const char *dest)
     return ret;
 }
 
+void iso_dir_find(IsoDir *dir, const char *name, IsoNode ***pos)
+{
+    *pos = &(dir->children);
+    while (**pos != NULL && strcmp((**pos)->name, name) < 0) {
+        *pos = &((**pos)->next);
+    } 
+}
+
+int iso_dir_exists(IsoDir *dir, const char *name, IsoNode ***pos)
+{
+    IsoNode **node;
+    
+    iso_dir_find(dir, name, &node);
+    if (pos) {
+        *pos = node;
+    }
+    return (*node != NULL && !strcmp((*node)->name, name)) ? 1 : 0;
+}
+
+int iso_dir_insert(IsoDir *dir, IsoNode *node, IsoNode **pos, 
+                   enum iso_replace_mode replace)
+{
+    if (*pos != NULL && !strcmp((*pos)->name, node->name)) {
+        /* a node with same name already exists */
+        if (replace == ISO_REPLACE_NEVER) {
+            return ISO_NODE_NAME_NOT_UNIQUE;
+        } else if (replace == ISO_REPLACE_ALWAYS) {
+            node->next = (*pos)->next;
+            (*pos)->parent = NULL;
+            (*pos)->next = NULL;
+            iso_node_unref(*pos);
+            *pos = node;
+            node->parent = dir;
+            return dir->nchildren;
+        } else {
+            /* CAN'T HAPPEN */
+            return ISO_WRONG_ARG_VALUE;
+        }
+    }
+
+    node->next = *pos;
+    *pos = node;
+    node->parent = dir;
+
+    return ++dir->nchildren;
+}
+
 int iso_node_new_root(IsoDir **root)
 {
     IsoDir *dir;
diff --git a/src/node.h b/src/node.h
index d7cda2d..5b819f5 100644
--- a/src/node.h
+++ b/src/node.h
@@ -123,4 +123,50 @@ int iso_node_is_valid_name(const char *name);
  */
 int iso_node_is_valid_link_dest(const char *dest);
 
+/**
+ * Find the position where to insert a node
+ * 
+ * @param dir
+ *      A valid dir. It can't be NULL
+ * @param name
+ *      The node name to search for. It can't be NULL
+ * @param pos
+ *      Will be filled with the position where to insert. It can't be NULL
+ */
+void iso_dir_find(IsoDir *dir, const char *name, IsoNode ***pos);
+
+/**
+ * Check if a node with the given name exists in a dir.
+ * 
+ * @param dir
+ *      A valid dir. It can't be NULL
+ * @param name
+ *      The node name to search for. It can't be NULL
+ * @param pos
+ *      If not NULL, will be filled with the position where to insert. If the
+ *      node exists, (**pos) will refer to the given node.
+ * @return
+ *      1 if node exists, 0 if not
+ */
+int iso_dir_exists(IsoDir *dir, const char *name, IsoNode ***pos);
+
+/**
+ * Inserts a given node in a dir, at the specified position.
+ * 
+ * @param dir
+ *     Dir where to insert. It can't be NULL
+ * @param node
+ *     The node to insert. It can't be NULL
+ * @param pos
+ *     Position where the node will be inserted. It is a pointer previously
+ *     obtained with a call to iso_dir_exists() or iso_dir_find(). 
+ *     It can't be NULL.
+ * @param replace 
+ *     Whether to replace an old node with the same name with the new node.
+ * @return
+ *     If success, number of children in dir. < 0 on error  
+ */
+int iso_dir_insert(IsoDir *dir, IsoNode *node, IsoNode **pos, 
+                   enum iso_replace_mode replace);
+
 #endif /*LIBISO_NODE_H_*/
diff --git a/src/tree.c b/src/tree.c
index 7d380b9..b584dc6 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -62,12 +62,8 @@ int iso_tree_add_new_dir(IsoDir *parent, const char *name, IsoDir **dir)
         return ISO_WRONG_ARG_VALUE;
     }
 
-    /* find place where to insert */
-    pos = &(parent->children);
-    while (*pos != NULL && strcmp((*pos)->name, name) < 0) {
-        pos = &((*pos)->next);
-    }
-    if (*pos != NULL && !strcmp((*pos)->name, name)) {
+    /* find place where to insert and check if it exists */
+    if (iso_dir_exists(parent, name, &pos)) {
         /* a node with same name already exists */
         return ISO_NODE_NAME_NOT_UNIQUE;
     }
@@ -97,15 +93,12 @@ int iso_tree_add_new_dir(IsoDir *parent, const char *name, IsoDir **dir)
     node->node.ctime = now;
     node->node.mtime = now;
 
-    /* add to dir */
-    node->node.parent = parent;
-    node->node.next = *pos;
-    *pos = (IsoNode*)node;
-
     if (dir) {
         *dir = node;
     }
-    return ++parent->nchildren;
+
+    /* add to dir */
+    return iso_dir_insert(parent, (IsoNode*)node, pos, ISO_REPLACE_NEVER);
 }
 
 /**
@@ -158,11 +151,7 @@ int iso_tree_add_new_symlink(IsoDir *parent, const char *name,
     }
 
     /* find place where to insert */
-    pos = &(parent->children);
-    while (*pos != NULL && strcmp((*pos)->name, name) < 0) {
-        pos = &((*pos)->next);
-    }
-    if (*pos != NULL && !strcmp((*pos)->name, name)) {
+    if (iso_dir_exists(parent, name, &pos)) {
         /* a node with same name already exists */
         return ISO_NODE_NAME_NOT_UNIQUE;
     }
@@ -199,15 +188,12 @@ int iso_tree_add_new_symlink(IsoDir *parent, const char *name,
     node->node.ctime = now;
     node->node.mtime = now;
 
-    /* add to dir */
-    node->node.parent = parent;
-    node->node.next = *pos;
-    *pos = (IsoNode*)node;
-
     if (link) {
         *link = node;
     }
-    return ++parent->nchildren;
+
+    /* add to dir */
+    return iso_dir_insert(parent, (IsoNode*)node, pos, ISO_REPLACE_NEVER);
 }
 
 /**
@@ -271,11 +257,7 @@ int iso_tree_add_new_special(IsoDir *parent, const char *name, mode_t mode,
     }
 
     /* find place where to insert */
-    pos = &(parent->children);
-    while (*pos != NULL && strcmp((*pos)->name, name) < 0) {
-        pos = &((*pos)->next);
-    }
-    if (*pos != NULL && !strcmp((*pos)->name, name)) {
+    if (iso_dir_exists(parent, name, &pos)) {
         /* a node with same name already exists */
         return ISO_NODE_NAME_NOT_UNIQUE;
     }
@@ -307,15 +289,12 @@ int iso_tree_add_new_special(IsoDir *parent, const char *name, mode_t mode,
     node->node.ctime = now;
     node->node.mtime = now;
 
-    /* add to dir */
-    node->node.parent = parent;
-    node->node.next = *pos;
-    *pos = (IsoNode*)node;
-
     if (special) {
         *special = node;
     }
-    return ++parent->nchildren;
+
+    /* add to dir */
+    return iso_dir_insert(parent, (IsoNode*)node, pos, ISO_REPLACE_NEVER);
 }
 
 /**
@@ -395,30 +374,24 @@ int iso_tree_add_node_builder(IsoImage *image, IsoDir *parent,
     name = iso_file_source_get_name(src);
 
     /* find place where to insert */
-    pos = &(parent->children);
-    while (*pos != NULL && strcmp((*pos)->name, name) < 0) {
-        pos = &((*pos)->next);
-    }
-    if (*pos != NULL && !strcmp((*pos)->name, name)) {
+    result = iso_dir_exists(parent, name, &pos);
+    free(name);
+    if (result) {
         /* a node with same name already exists */
         return ISO_NODE_NAME_NOT_UNIQUE;
     }
-    free(name);
 
     result = builder->create_node(builder, image, src, &new);
     if (result < 0) {
         return result;
     }
 
-    /* finally, add node to parent */
-    new->parent = parent;
-    new->next = *pos;
-    *pos = new;
-
     if (node) {
         *node = new;
     }
-    return ++parent->nchildren;
+
+    /* finally, add node to parent */
+    return iso_dir_insert(parent, (IsoNode*)new, pos, ISO_REPLACE_NEVER);
 }
 
 int iso_tree_add_node(IsoImage *image, IsoDir *parent, const char *path,
@@ -513,11 +486,7 @@ int iso_add_dir_src_rec(IsoImage *image, IsoDir *parent, IsoFileSource *dir)
 
         /* find place where to insert */
         flag = 0;
-        pos = &(parent->children);
-        while (*pos != NULL && strcmp((*pos)->name, name) < 0) {
-            pos = &((*pos)->next);
-        }
-        if (*pos != NULL && !strcmp((*pos)->name, name)) {
+        if (iso_dir_exists(parent, name, &pos)) {
             flag = 1;
             if (action == 1 && image->recOpts.replace == 0) {
                 action = 2;
@@ -569,21 +538,8 @@ int iso_add_dir_src_rec(IsoImage *image, IsoDir *parent, IsoFileSource *dir)
         }
 
         /* ok, node has correctly created, we need to add it */
-        if (flag) {
-            /* replace node */
-            new->next = (*pos)->next;
-            (*pos)->parent = NULL;
-            (*pos)->next = NULL;
-            iso_node_unref(*pos);
-            *pos = new;
-            new->parent = parent;
-        } else {
-            /* just add */
-            new->next = *pos;
-            *pos = new;
-            new->parent = parent;
-            ++parent->nchildren;
-        }
+        iso_dir_insert(parent, new, pos, flag ? ISO_REPLACE_ALWAYS :
+                                         ISO_REPLACE_NEVER);
 
         /* finally, if the node is a directory we need to recurse */
         if (new->type == LIBISO_DIR) {