Re: [PATCH 1/3] xen: check required Xen features

[Juergen Gross]

On 22.04.21 17:26, Stefano Stabellini wrote:
> On Thu, 22 Apr 2021, Juergen Gross wrote:
> > Linux kernel is not supported to run on Xen versions older than 4.0.
> >
> > Add tests for required Xen features always being present in Xen 4.0
> > and newer.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   drivers/xen/features.c | 18 ++++++++++++++++++
> >   1 file changed, 18 insertions(+)
> >
> > diff --git a/drivers/xen/features.c b/drivers/xen/features.c
> > index 25c053b09605..60503299c9bc 100644
> > --- a/drivers/xen/features.c
> > +++ b/drivers/xen/features.c
> > @@ -9,13 +9,26 @@
> >   #include <linux/types.h>
> >   #include <linux/cache.h>
> >   #include <linux/export.h>
> > +#include <linux/printk.h>
> >   
> >   #include <asm/xen/hypercall.h>
> >   
> > +#include <xen/xen.h>
> >   #include <xen/interface/xen.h>
> >   #include <xen/interface/version.h>
> >   #include <xen/features.h>
> >   
> > +/*
> > + * Linux kernel expects at least Xen 4.0.
> > + *
> > + * Assume some features to be available for that reason (depending on guest
> > + * mode, of course).
> > + */
> > +#define chk_feature(f) {						\
> > +		if (!xen_feature(f))					\
> > +			pr_err("Xen: feature %s not available!\n", #f);	\
> > +	}
>
> I think this could be done as a static inline function in
> include/xen/features.h. That way it would be available everywhere. Also,
> static inlines are better than macro when it is possible to use them in
> terms of code safety.

It is a macro in order to have only one parameter.

And being a local macro is rendering the code safety reasoning moot.

Additionally I don't want this testing to be scattered all over the
code base. It should be done in one place only.


Juergen

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