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Date: Tue, 8 Aug 2017 20:35:05 +0200
From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Juergen Gross <jgross@suse.com>, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH] lib: Add test module for CONFIG_DEBUG_VIRTUAL
Message-ID: <20170808183505.GS27873@wotan.suse.de>
References: <20170808164035.26725-1-f.fainelli@gmail.com>
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 <eabb661e-0442-b274-2c79-95bc52f2a79b@gmail.com>
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On Tue, Aug 08, 2017 at 11:04:11AM -0700, Florian Fainelli wrote:
> On 08/08/2017 10:57 AM, Luis R. Rodriguez wrote:
> > On Tue, Aug 08, 2017 at 09:40:26AM -0700, Florian Fainelli wrote:
> >> Add a test module that allows testing that CONFIG_DEBUG_VIRTUAL works
> >> correctly, at least that it can catch invalid calls to virt_to_phys()
> >> against the non-linear kernel virtual address map.
> >>
> >> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> >> ---
> 
> >> +static int __init test_debug_virtual_init(void)
> >> +{
> >> +	phys_addr_t pa;
> >> +	void *va;
> >> +
> >> +	va = (void *)VMALLOC_START;
> >> +	pa = virt_to_phys(va);
> >> +
> >> +	pr_info("PA: %pa for VA: 0x%lx\n", &pa, (unsigned long)va);
> >> +
> >> +	foo = kzalloc(sizeof(*foo), GFP_KERNEL);
> >> +	if (!foo)
> >> +		return -ENOMEM;
> >> +
> >> +	pa = virt_to_phys(foo);
> >> +	va = foo;
> >> +	pr_info("PA: %pa for VA: 0x%lx\n", &pa, (unsigned long)va);
> > 
> > Should there be a tests here of some sort? When should this fail, why?
> 
> There is no test per-se, the kernel will produce warning with
> CONFIG_DEBUG_VIRTUAL telling you that what you are doing is wrong.
> 
> > There is no docs on this self test, could one be added?
> 
> I suppose I could add one even though that just means pointing out the
> code that produces the warning?

A /* note */ indicating what you just said above would suffice then but
typically tests return back to userspace an error, so another option
would be to see if one could get a return value that an error happened
and return that back to the module init. Grepping just for warning for
an error seems error prone.

  Luis