Re: [RESEND][PATCH v2 5/7] xen: include xen/guest_access.h rather than asm/guest_access.h

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 18/08/2020 17:23, Jan Beulich wrote:
> On 18.08.2020 18:20, Julien Grall wrote:
> > On 18/08/2020 17:04, Jan Beulich wrote:
> > > On 18.08.2020 15:14, Julien Grall wrote:
> > > > On 18/08/2020 12:32, Jan Beulich wrote:
> > > > > On 18.08.2020 10:58, Julien Grall wrote:
> > > > > > > One option. Personally I'd prefer to avoid introduction of yet another
> > > > > > > constant, by leveraging __XEN_GUEST_ACCESS_H__ instead.
> > > > > > I thought about it but it doesn't prevent new inclusions of asm/guest_access.h. 
> > > > > > For instance, the following would still compile:
> > > > > >
> > > > > > #include <xen/guest_access.h>
> > > > > >
> > > > > > [...]
> > > > > >
> > > > > > #include <asm/guest_access.h>
> > > > > But where's the problem with this? The first #include will already
> > > > > have resulted in the inclusion of asm/guest_access.h, so the second
> > > > > #include is simply a no-op.
> > > > A couple of reasons:
> > > >      1) I don't consider this solving completely your original request [1]
> > > >      2) I don't see how this is more important to prevent including 
> > > > <asm/guest_access.h> before and not after. Both will still compile fine, we just want to avoid 
> > > > it.
> > > >
> > > >
> > > > [1] "Is there any chance you could take measures to avoid new inclusions of 
> > > > asm/guest_access.h to appear?"
> > > Is
> > >
> > > #include <xen/guest_access.h>
> > > [...]
> > > #include <asm/guest_access.h>
> > >
> > > actually a problem (as opposed to an asm/ include without any include
> > > of the xen/ one at all)?
> > Neither of them are really a problem today. So it is not entirely clear why we 
> > would want to prevent one and not the other.
> If neither is a problem, why the conversion?
As I wrote in the commit message, some of the helpers will be moved from 
asm/guest_access.h. So existing users of asm/guest_access.h may not 
compiled anymore.
If you are not using any helpers from xen/guest_access.h, then you could 
theoritically only include asm/guest_access.h. But they are quite 
limited or maybe don't even exist.
Actually xen/guest_access.h was included from asm/guest_access.h. But 
there are compilation issues if you try to include xen/guest_access.h 
from asm/guest_access.h.
Therefore it is better to request everyone to include 
<xen/guest_access.h>. With that you get all the guest access helpers 
rather than just the arch specific one.
Cheers,

--
Julien Grall