Add strlen_user() (will be needed for PXE API extensions)

src/arch/i386/include/librm.h

@@ -193,6 +193,18 @@ memset_user ( userptr_t buffer, off_t offset, int c, size_t len ) {
 	memset ( ( ( void * ) buffer + offset ), c, len );
 }
 
+/**
+ * Find length of NUL-terminated string in user buffer
+ *
+ * @v buffer		User buffer
+ * @v offset		Offset within buffer
+ * @ret len		Length of string (excluding NUL)
+ */
+static inline __attribute__ (( always_inline )) size_t
+strlen_user ( userptr_t buffer, off_t offset ) {
+	return strlen ( ( void * ) buffer + offset );
+}
+
 /**
  * Convert virtual address to user buffer
  *