[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH 01/11] xen: reserve flags for internal usage in xen_domctl_createdomain

Hi Jan,

On 28/09/2021 13:05, Jan Beulich wrote:
On 23.09.2021 11:54, Julien Grall wrote:
On 23/09/2021 08:11, Penny Zheng wrote:
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>

We are passing an extra special boolean flag at domain creation to
specify whether we want to the domain to be privileged (i.e. dom0) or
not. Another flag will be introduced later in this series.

Reserve bits 16-31 from the existing flags bitfield in struct
xen_domctl_createdomain for internal Xen usage.

I am a bit split with this approach. This feels a bit of a hack to
reserve bits for internal purpose in external headers. But at the same
time I can see how this is easier to deal with it over repurposing the
last argument of domain_create().

I actually have trouble seeing why that's easier. It is a common thing
to widen a bool to "unsigned int flags" when more than one control is

I was suggesting this is easier for the following two reasons:
  1) All the option flags (internal and external) are in a single place.
2) Reduce the risk to make a mistake when widening the field. In particular in the context of backporting. Although, this looks unlikely here.

Plus this makes things needlessly harder once (in the future)
the low 16 bits are exhausted in the public interface.

That's why I suggested this sounds like a hack. At the same time the split between external vs internal option is a bit more a pain for the developper. So I didn't feel pushing for one vs the other. That said, I will not argue against if you want to push for repurposing the last argument.


Julien Grall



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.