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

[Olaf Hering <olaf@xxxxxxxxx>]

On Wed, Jan 29, Ian Campbell wrote:

> On Wed, 2014-01-29 at 16:06 +0100, Olaf Hering wrote:
> > 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?
> You should add a #define LIBXL_HAVE_FOO to libxl.h, there are a few
> examples in there already.

I will add such a define.

> There is no need to make the actual field conditional -- that would
> actually be wrong since it would modify the ABI depending on what the
> application asked for, meaning it would differ from how libxl was
> actually built. An application which us using an ABI before 4.5 simply
> won't think to touch this field.

I meant the access of the field in libvirt, like "p->discard_enable = val;".
Putting such code into #ifdef LIBXL_HAVE_FOO is fine.

Olaf

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