[efi] Add efi_asprintf() and efi_vasprintf()

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

src/interface/efi/efi_strings.c

@@ -25,6 +25,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <stddef.h>
 #include <stdarg.h>
+#include <stdlib.h>
+#include <errno.h>
 #include <ipxe/vsprintf.h>
 #include <ipxe/efi/efi_strings.h>
 
@@ -150,3 +152,45 @@ int efi_ssnprintf ( wchar_t *wbuf, ssize_t swsize, const char *fmt, ... ) {
 	va_end ( args );
 	return len;
 }
+
+/**
+ * Write a formatted string to newly allocated memory
+ *
+ * @v wstrp		Pointer to hold allocated string
+ * @v fmt		Format string
+ * @v args		Arguments corresponding to the format string
+ * @ret len		Length of formatted string (in wide characters)
+ */
+int efi_vasprintf ( wchar_t **wstrp, const char *fmt, va_list args ) {
+	size_t len;
+	va_list args_tmp;
+
+	/* Calculate length needed for string */
+	va_copy ( args_tmp, args );
+	len = ( efi_vsnprintf ( NULL, 0, fmt, args_tmp ) + 1 );
+	va_end ( args_tmp );
+
+	/* Allocate and fill string */
+	*wstrp = malloc ( len * sizeof ( **wstrp ) );
+	if ( ! *wstrp )
+		return -ENOMEM;
+	return efi_vsnprintf ( *wstrp, len, fmt, args );
+}
+
+/**
+ * Write a formatted string to newly allocated memory
+ *
+ * @v wstrp		Pointer to hold allocated string
+ * @v fmt		Format string
+ * @v ...		Arguments corresponding to the format string
+ * @ret len		Length of formatted string (in wide characters)
+ */
+int efi_asprintf ( wchar_t **wstrp, const char *fmt, ... ) {
+	va_list args;
+	int len;
+
+	va_start ( args, fmt );
+	len = efi_vasprintf ( wstrp, fmt, args );
+	va_end ( args );
+	return len;
+}