linux-kernel - Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'

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Message-ID: <58eca97c-f72e-66a7-2696-611124ce0943@redhat.com>
Date:   Fri, 8 Jan 2021 16:04:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        zhenwei pi <pizhenwei@...edance.com>
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] misc: pvpanic: introduce module parameter 'events'

On 08/01/21 15:07, Greg KH wrote:
>>   
>>   static void __iomem *base;
>> +static unsigned int events = PVPANIC_PANICKED | PVPANIC_CRASH_LOADED;
>> +module_param(events, uint, 0644);
>> +MODULE_PARM_DESC(events, "set event limitation of pvpanic device");
> I do not understand you wanting a module parameter as well as a sysfs
> file.  Why is this needed?  Why are you spreading this information out
> across different apis and locations?

It can be useful to disable some functionality, for example in case you 
want to fake running on an older virtualization host.  This can be done 
for debugging reasons, or to keep uniform handling across a fleet that 
is running different versions of QEMU.

Paolo

> Again, adding module parameters is almost never a good idea anymore,
> they are a pain to manage and use.