fdt: Add functions to retrieve strings

Given a device tree node, a property name and an index, the new function
fdt_stringlist_get() will return a pointer to the index'th string in the
property's value and return its length (or an error code on failure) in
an output argument.

Signed-off-by: Thierry Reding <treding@nvidia.com>
[Fix some -Wshadow warnings --dwg]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 45 insertions, 0 deletions

diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index 2d74c37..e5b3136 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -593,6 +593,51 @@ int fdt_stringlist_search(const void *fdt, int nodeoffset, const char *property,
 	return -FDT_ERR_NOTFOUND;
 }
 
+const char *fdt_stringlist_get(const void *fdt, int nodeoffset,
+			       const char *property, int idx,
+			       int *lenp)
+{
+	const char *list, *end;
+	int length;
+
+	list = fdt_getprop(fdt, nodeoffset, property, &length);
+	if (!list) {
+		if (lenp)
+			*lenp = length;
+
+		return NULL;
+	}
+
+	end = list + length;
+
+	while (list < end) {
+		length = strnlen(list, end - list) + 1;
+
+		/* Abort if the last string isn't properly NUL-terminated. */
+		if (list + length > end) {
+			if (lenp)
+				*lenp = -FDT_ERR_BADVALUE;
+
+			return NULL;
+		}
+
+		if (idx == 0) {
+			if (lenp)
+				*lenp = length - 1;
+
+			return list;
+		}
+
+		list += length;
+		idx--;
+	}
+
+	if (lenp)
+		*lenp = -FDT_ERR_NOTFOUND;
+
+	return NULL;
+}
+
 int fdt_node_check_compatible(const void *fdt, int nodeoffset,
 			      const char *compatible)
 {