Re: [PATCH] libxl: preserve errno in libxl__xcinfo2xlinfo()

[Jason Andryuk <jason.andryuk@xxxxxxx>]

On 2025-08-27 01:57, Jan Beulich wrote:
> Callers observing errors elsewhere may be confused by the ENOSYS that
> the Flask operation would yield on a Flask-disabled hypervisor.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Of course I don't know whether clobbering errno is perhaps deemed "fine"
> in libxl.
I wonder if it would be better to special case 
libxl_flask_sid_to_context() to preserve errno on ENOSYS.  flask 
returning ENOSYS is common, but libxl_flask_sid_to_context() can 
legitimately have error.
I guess this is fine if we want to use this approach:

Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>

> --- a/tools/libs/light/libxl_domain.c
> +++ b/tools/libs/light/libxl_domain.c
> @@ -277,6 +277,7 @@ void libxl__xcinfo2xlinfo(libxl_ctx *ctx
>                             libxl_dominfo *xlinfo)
>   {
>       size_t size;
> +    int saved_errno = errno;
>   
>       memcpy(&(xlinfo->uuid), xcinfo->handle, sizeof(xen_domain_handle_t));
>       xlinfo->domid = xcinfo->domain;
> @@ -284,6 +285,7 @@ void libxl__xcinfo2xlinfo(libxl_ctx *ctx
>       if (libxl_flask_sid_to_context(ctx, xlinfo->ssidref,
>                                      &xlinfo->ssid_label, &size) < 0)
>           xlinfo->ssid_label = NULL;
> +    errno = saved_errno;
>   
>       xlinfo->dying      = !!(xcinfo->flags&XEN_DOMINF_dying);
>       xlinfo->shutdown   = !!(xcinfo->flags&XEN_DOMINF_shutdown);