Re: [PATCH] libxl: add option for discard support to xl disk configuration

[Olaf Hering <olaf@aepfle.de>]

On Tue, Jan 28, Olaf Hering wrote:

> Handle new option discard=on|off for disk configuration. It is supposed
> to disable discard support if file based backing storage was
> intentionally created non-sparse to avoid fragmentation of the file.

> +++ b/tools/libxl/libxl_types.idl
> @@ -415,6 +415,7 @@ libxl_device_disk = Struct("device_disk", [
>      ("removable", integer),
>      ("readwrite", integer),
>      ("is_cdrom", integer),
> +    ("discard_enable", integer),

This new field changes the API, _libxl_types.h:struct libxl_device_disk
gets a new member. How should code using this new flag recognize if its
present? If it is supposed to be part of a new libxl-4.5 API then
out-of-tree code could put the code into #ifdef LIBXL_API_VERSION >= X.
If not, how should it be done?

For my own purpose I will overload ->readwrite to carry the discard flag
and to preserve the ABI.

Olaf