Re: XC_PAGE_SIZE or XEN_PAGE_SIZE?

["Jan Beulich" <JBeulich@suse.com>]

>>> On 02.12.16 at 08:49, <andr2000@gmail.com> wrote:
> While working on display protocol I found that there is no(?) common
> 
> ???_PAGE_SIZE define I can use for both Xen and Linux kernel:
> 
> Xen defines XC_PAGE_SIZE which is also used in Linux user-space and
> 
> kernel has XEN_PAGE_SIZE, but no XC_PAGE_SIZE.
> 
> So, the question is which define should I use?

In the abstract protocol there should be no need for this other
than in comments (as is the case for all other protocols with the
exception of vscsiif, which had a need to define its own
VSCSIIF_PAGE_SIZE), where I think just PAGE_SIZE will be fine.
In the end, frontend and backend are required to agree on a
page size via some side channel anyway, which usually is
achieved by base architecture assumptions (after all both run
on the same physical machine and hence with the same set of
architecture prerequisites). Arguably this is not an optimal model
(namely on architectures supporting varying page sizes), but if
we were to change it we should probably do so for all protocols.

In the implementation you use the manifest constant available: If
your code is in user space, use XC_PAGE_SIZE. In the kernel you'd
obviously use XEN_PAGE_SIZE.

Jan


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