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Subject: Re: [PATCH 1/3] xen: check required Xen features
To:     Stefano Stabellini <sstabellini@kernel.org>
Cc:     xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>
References: <20210422151007.2205-1-jgross@suse.com>
 <20210422151007.2205-2-jgross@suse.com>
 <alpine.DEB.2.21.2104220823160.5018@sstabellini-ThinkPad-T480s>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <6f3a782b-0d1d-e86e-998b-bc3b46e1f4c3@suse.com>
Date:   Thu, 22 Apr 2021 17:32:32 +0200
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From: Juergen Gross <jgross@suse.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
 Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Peter Zijlstra <peterz@infradead.org>
Message-ID: <6f3a782b-0d1d-e86e-998b-bc3b46e1f4c3@suse.com>
Subject: Re: [PATCH 1/3] xen: check required Xen features
References: <20210422151007.2205-1-jgross@suse.com>
 <20210422151007.2205-2-jgross@suse.com>
 <alpine.DEB.2.21.2104220823160.5018@sstabellini-ThinkPad-T480s>
In-Reply-To: <alpine.DEB.2.21.2104220823160.5018@sstabellini-ThinkPad-T480s>

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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@suse.com>
>> ---
>>   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>
>>  =20
>>   #include <asm/xen/hypercall.h>
>>  =20
>> +#include <xen/xen.h>
>>   #include <xen/interface/xen.h>
>>   #include <xen/interface/version.h>
>>   #include <xen/features.h>
>>  =20
>> +/*
>> + * 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);	\
>> +	}
>=20
> 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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