[PATCH 4/4] Create a new property value that means 'undefined'.

[John Bonesio]

When updating existing nodes in a device tree merge operation, properties
can be removed by setting the value to /undef-prop/.

if /undef-prop/ is assigned to a property that doesn't exist, the property
is treated the same as if it had not been declared.

Signed-off-by: John Bonesio <bones at secretlab.ca>
---

 dtc-lexer.l  |   14 ++++++++++----
 dtc-parser.y |    6 ++++++
 dtc.h        |    7 +++++++
 flattree.c   |    3 +++
 livetree.c   |   38 +++++++++++++++++++++++++++++++++-----
 5 files changed, 59 insertions(+), 9 deletions(-)

diff --git a/dtc-lexer.l b/dtc-lexer.l
index 216a3d2..efa89b4 100644
--- a/dtc-lexer.l
+++ b/dtc-lexer.l
@@ -102,6 +102,12 @@ static int pop_input_file(void);
 			return DT_REMOVENODE;
 		}
 
+<*>"/undef-prop/"	{
+			DPRINT("Keyword: /undef-prop/\n");
+			BEGIN_DEFAULT();
+			return DT_UNDEFINED;
+		}
+
 <*>{LABEL}:	{
 			DPRINT("Label: %s\n", yytext);
 			yylval.labelref = xstrdup(yytext);
@@ -116,10 +122,10 @@ static int pop_input_file(void);
 		}
 
 
-<*>\&{LABEL}    {       /* label reference without the braces*/
-                        DPRINT("Ref: %s\n", yytext+1);
-                        yylval.labelref = xstrdup(yytext+1);
-                        return DT_REF;
+<*>\&{LABEL}	{       /* label reference without the braces*/
+			DPRINT("Ref: %s\n", yytext+1);
+			yylval.labelref = xstrdup(yytext+1);
+	    		return DT_REF;
 		}
 
 <*>"&{"{LABEL}{PATHCHAR}*\} { /* label and/or path refererence with braces */
diff --git a/dtc-parser.y b/dtc-parser.y
index 0a74c86..ac9cfd7 100644
--- a/dtc-parser.y
+++ b/dtc-parser.y
@@ -56,6 +56,7 @@ static unsigned long long eval_literal(const char *s, int base, int bits);
 %token DT_V1
 %token DT_MEMRESERVE
 %token DT_REMOVENODE
+%token DT_UNDEFINED
 %token <propnodename> DT_PROPNODENAME
 %token <literal> DT_LITERAL
 %token <cbase> DT_BASE
@@ -178,6 +179,11 @@ propdef:
 		{
 			$$ = build_property($1, empty_data);
 		}
+	| DT_PROPNODENAME '=' DT_UNDEFINED ';'
+		{
+			$$ = build_property($1, empty_data);
+			undefine_property($$)
+		}
 	| DT_LABEL propdef
 		{
 			add_label(&$2->labels, $1);
diff --git a/dtc.h b/dtc.h
index a7f3667..b3fca6e 100644
--- a/dtc.h
+++ b/dtc.h
@@ -130,7 +130,12 @@ struct label {
 	struct label *next;
 };
 
+#define PROP_DEFINED (0)
+#define PROP_UNDEFINED (1)
+
 struct property {
+	int undefined;  /* if the property is set to undefined, this feild is
+	                   set to PROP_UNDEFINED */
 	char *name;
 	struct data val;
 
@@ -170,6 +175,7 @@ void add_label(struct label **labels, char *label);
 struct property *build_property(char *name, struct data val);
 struct property *chain_property(struct property *first, struct property *list);
 struct property *reverse_properties(struct property *first);
+void undefine_property(struct property *prop);
 
 struct node *build_node(struct property *proplist, struct node *children);
 struct node *name_node(struct node *node, char *name);
@@ -177,6 +183,7 @@ struct node *chain_node(struct node *first, struct node *list);
 struct node *merge_nodes(struct node *old_node, struct node *new_node);
 
 void add_property(struct node *node, struct property *prop);
+void remove_property(struct node *node, struct property *prop);
 void add_child(struct node *parent, struct node *child);
 void remove_child(struct node *parent, struct node *child);
 
diff --git a/flattree.c b/flattree.c
index ead0332..00439e9 100644
--- a/flattree.c
+++ b/flattree.c
@@ -275,6 +275,9 @@ static void flatten_tree(struct node *tree, struct emitter *emit,
 	for_each_property(tree, prop) {
 		int nameoff;
 
+		if (prop->undefined)
+			continue;
+
 		if (streq(prop->name, "name"))
 			seen_name_prop = 1;
 
diff --git a/livetree.c b/livetree.c
index bf8796b..2ef734d 100644
--- a/livetree.c
+++ b/livetree.c
@@ -51,6 +51,11 @@ struct property *build_property(char *name, struct data val)
 	return new;
 }
 
+void undefine_property(struct property *prop)
+{
+	prop->undefined = 1;
+}
+
 struct property *chain_property(struct property *first, struct property *list)
 {
 	assert(first->next == NULL);
@@ -121,11 +126,15 @@ struct node *merge_nodes(struct node *old_node, struct node *new_node)
 		/* Look for a collision, set new value if there is */
 		for_each_property(old_node, old_prop) {
 			if (streq(old_prop->name, new_prop->name)) {
-				/* Add new labels to old property */
-				for_each_label(new_prop->labels, l)
-					add_label(&old_prop->labels, l->label);
-
-				old_prop->val = new_prop->val;
+				if (new_prop->undefined) {
+					remove_property(old_node, old_prop);
+				} else {
+					/* Add new labels to old property */
+					for_each_label(new_prop->labels, l)
+						add_label(&old_prop->labels, l->label);
+
+					old_prop->val = new_prop->val;
+				}
 				free(new_prop);
 				new_prop = NULL;
 				break;
@@ -188,6 +197,25 @@ void add_property(struct node *node, struct property *prop)
 	*p = prop;
 }
 
+void remove_property(struct node *node, struct property *prop)
+{
+	struct property **p;
+	int found = 0;
+
+	p = &node->proplist;
+	while (*p) {
+		if (*p == prop) {
+			*p = (*p)->next;
+			found = 1;
+			break;
+		}
+		p = &((*p)->next);
+	}
+	/* property not in the node? it's probably an error, so flag it. */
+	assert(found);
+}
+
+
 void add_child(struct node *parent, struct node *child)
 {
 	struct node **p;