[efi] Expose efi_path_next() utility function

Provide a single central implementation of the logic for stepping
through elements of an EFI device path.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

3 files changed, 41 insertions, 15 deletions

diff --git a/src/include/ipxe/efi/efi_path.h b/src/include/ipxe/efi/efi_path.h
index 76ded72..18810a7 100644
--- a/src/include/ipxe/efi/efi_path.h
+++ b/src/include/ipxe/efi/efi_path.h
@@ -22,6 +22,8 @@ struct ib_srp_device;
 struct usb_function;
 
 extern EFI_DEVICE_PATH_PROTOCOL *
+efi_path_next ( EFI_DEVICE_PATH_PROTOCOL *path );
+extern EFI_DEVICE_PATH_PROTOCOL *
 efi_path_end ( EFI_DEVICE_PATH_PROTOCOL *path );
 extern size_t efi_path_len ( EFI_DEVICE_PATH_PROTOCOL *path );
 extern EFI_DEVICE_PATH_PROTOCOL * efi_paths ( EFI_DEVICE_PATH_PROTOCOL *first,
diff --git a/src/interface/efi/efi_local.c b/src/interface/efi/efi_local.c
index d8edb62..f54f5da 100644
--- a/src/interface/efi/efi_local.c
+++ b/src/interface/efi/efi_local.c
@@ -419,14 +419,15 @@ static int efi_local_open_resolved ( struct efi_local *local,
  * Open specified path
  *
  * @v local		Local file
- * @v path		Path to file
+ * @v filename		Path to file relative to our own image
  * @ret rc		Return status code
  */
-static int efi_local_open_path ( struct efi_local *local, const char *path ) {
-	FILEPATH_DEVICE_PATH *fp = container_of ( efi_loaded_image->FilePath,
-						  FILEPATH_DEVICE_PATH, Header);
-	size_t fp_len = efi_path_len ( &fp->Header );
-	char base[ fp_len / 2 /* Cannot exceed this length */ ];
+static int efi_local_open_path ( struct efi_local *local,
+				 const char *filename ) {
+	EFI_DEVICE_PATH_PROTOCOL *path = efi_loaded_image->FilePath;
+	EFI_DEVICE_PATH_PROTOCOL *next;
+	FILEPATH_DEVICE_PATH *fp;
+	char base[ efi_path_len ( path ) / 2 /* Cannot exceed this length */ ];
 	size_t remaining = sizeof ( base );
 	size_t len;
 	char *resolved;
@@ -436,13 +437,12 @@ static int efi_local_open_path ( struct efi_local *local, const char *path ) {
 	/* Construct base path to our own image, if possible */
 	memset ( base, 0, sizeof ( base ) );
 	tmp = base;
-	while ( fp && ( fp->Header.Type != END_DEVICE_PATH_TYPE ) ) {
+	for ( ; ( next = efi_path_next ( path ) ) ; path = next ) {
+		fp = container_of ( path, FILEPATH_DEVICE_PATH, Header );
 		len = snprintf ( tmp, remaining, "%ls", fp->PathName );
 		assert ( len < remaining );
 		tmp += len;
 		remaining -= len;
-		fp = ( ( ( void * ) fp ) + ( ( fp->Header.Length[1] << 8 ) |
-					     fp->Header.Length[0] ) );
 	}
 	DBGC2 ( local, "LOCAL %p base path \"%s\"\n",
 		local, base );
@@ -454,7 +454,7 @@ static int efi_local_open_path ( struct efi_local *local, const char *path ) {
 	}
 
 	/* Resolve path */
-	resolved = resolve_path ( base, path );
+	resolved = resolve_path ( base, filename );
 	if ( ! resolved ) {
 		rc = -ENOMEM;
 		goto err_resolve;
diff --git a/src/interface/efi/efi_path.c b/src/interface/efi/efi_path.c
index 1a95a3b..937d3c7 100644
--- a/src/interface/efi/efi_path.c
+++ b/src/interface/efi/efi_path.c
@@ -41,18 +41,42 @@
  */
 
 /**
+ * Find next element in device path
+ *
+ * @v path		Device path, or NULL
+ * @v next		Next element in device path, or NULL if at end
+ */
+EFI_DEVICE_PATH_PROTOCOL * efi_path_next ( EFI_DEVICE_PATH_PROTOCOL *path ) {
+
+	/* Check for non-existent device path */
+	if ( ! path )
+		return NULL;
+
+	/* Check for end of device path */
+	if ( path->Type == END_DEVICE_PATH_TYPE )
+		return NULL;
+
+	/* Move to next component of the device path */
+	path = ( ( ( void * ) path ) +
+		 /* There's this amazing new-fangled thing known as
+		  * a UINT16, but who wants to use one of those? */
+		 ( ( path->Length[1] << 8 ) | path->Length[0] ) );
+
+	return path;
+}
+
+/**
  * Find end of device path
  *
  * @v path		Device path, or NULL
  * @ret path_end	End of device path, or NULL
  */
 EFI_DEVICE_PATH_PROTOCOL * efi_path_end ( EFI_DEVICE_PATH_PROTOCOL *path ) {
+	EFI_DEVICE_PATH_PROTOCOL *next;
 
-	while ( path && ( path->Type != END_DEVICE_PATH_TYPE ) ) {
-		path = ( ( ( void * ) path ) +
-			 /* There's this amazing new-fangled thing known as
-			  * a UINT16, but who wants to use one of those? */
-			 ( ( path->Length[1] << 8 ) | path->Length[0] ) );
+	/* Find end of device path */
+	while ( ( next = efi_path_next ( path ) ) != NULL ) {
+		path = next;
 	}
 
 	return path;