Re: [PATCH RFC] x86+libxl: correct p2m (shadow) memory pool size calculation

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Apr 22, 2022 at 12:57:03PM +0200, Jan Beulich wrote:
> The reference "to shadow the resident processes" is applicable to
> domains (potentially) running in shadow mode only. Adjust the
> calculations accordingly.
> 
> In dom0_paging_pages() also take the opportunity and stop open-coding
> DIV_ROUND_UP().
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> RFC: I'm pretty sure I can't change a public libxl function (deprecated
>      or not) like this, but I also don't know how I should go about
>      doing so (short of introducing a brand new function and leaving the
>      existing one broken).

You have to play with LIBXL_API_VERSION, see for example:

1e3304005e libxl: Make libxl_retrieve_domain_configuration async

> 
> --- a/tools/include/libxl_utils.h
> +++ b/tools/include/libxl_utils.h
> @@ -23,7 +23,10 @@ const
>  #endif
>  char *libxl_basename(const char *name); /* returns string from strdup */
>  
> -unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb, 
> unsigned int smp_cpus);
> +unsigned long libxl_get_required_shadow_memory(unsigned long maxmem_kb,
> +                                               unsigned int smp_cpus,
> +                                               libxl_domain_type type,
> +                                               bool hap);

Iff we are to change this anyway, we might as well rename the
function and introduce a proper
libxl_get_required_{paging,p2m}_memory?

It seems wrong to have a function explicitly named 'shadow' that takes
a 'hap' parameter.

If you introduce a new function there's no need to play with the
LIBXL_API_VERSION and you can just add a new LIBXL_HAVE_FOO define.

Thanks, Roger.