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



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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