linux-kernel - Re: [PATCH] zcrypt: handle AP Info notification from CHSC SEI command

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Date:   Thu, 21 Feb 2019 13:12:40 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Harald Freudenberger <freude@...ux.ibm.com>
Cc:     Sebastian Ott <sebott@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        oberpar@...ux.ibm.com, pmorel@...ux.ibm.com, pasic@...ux.ibm.com
Subject: Re: [PATCH] zcrypt: handle AP Info notification from CHSC SEI
 command

On Thu, 21 Feb 2019 11:42:25 +0100
Harald Freudenberger <freude@...ux.ibm.com> wrote:

> On 30.01.19 19:32, Sebastian Ott wrote:
> > On Wed, 30 Jan 2019, Tony Krowiak wrote:  

> >>  /*
> >> +* A config change has happened, Force an ap bus rescan.
> >> +*/
> >> +void ap_bus_cfg_chg(void)
> >> +{
> >> +	AP_DBF(DBF_INFO, "%s config change, forcing bus rescan\n", __func__);
> >> +
> >> +	ap_bus_force_rescan();
> >> +}
> >> +EXPORT_SYMBOL(ap_bus_cfg_chg);  
> > There is no need for the export symbol - you don't call that function
> > from module code.  
> That's what I have learned now: You don't need to export a symbol
> as long as the symbol is only called in static code parts of the kernel.
> But you need to export it when it is intended to be used by code
> which sits in a kernel module. So now the big question:
> How does a provider of a function in the kernel know, if the caller is in static
> code or in module code ? And ... maybe this may even change over
> the time. So my recommendation is to always export the symbol with
> the EXPORT_SYMBOL macro. This way you don't need to change the
> code providing a function when the caller code changes or additional
> code uses the symbol.
> 
> Other opinions ?

Well, if you know it will be called from module code in upcoming
patches, export it. If not, I consider it the choice of the maintainer.
You can easily add the export later on, if needed, anyway, and I don't
consider changing the code a problem.

In this particular case, both exporting and not exporting looked like
reasonable choices to me.