linux-kernel - Re: [PATCH v10 01/16] s390/vfio-ap: add version vfio

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Message-ID: <20200825120432.13a1b444.cohuck@redhat.com>
Date:   Tue, 25 Aug 2020 12:04:32 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        mjrosato@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com, frankja@...ux.ibm.com, david@...hat.com,
        imbrenda@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v10 01/16] s390/vfio-ap: add version vfio_ap module

On Fri, 21 Aug 2020 15:56:01 -0400
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> Let's set a version for the vfio_ap module so that automated regression
> tests can determine whether dynamic configuration tests can be run or
> not.
> 
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_drv.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> index be2520cc010b..f4ceb380dd61 100644
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> @@ -17,10 +17,12 @@
>  
>  #define VFIO_AP_ROOT_NAME "vfio_ap"
>  #define VFIO_AP_DEV_NAME "matrix"
> +#define VFIO_AP_MODULE_VERSION "1.2.0"
>  
>  MODULE_AUTHOR("IBM Corporation");
>  MODULE_DESCRIPTION("VFIO AP device driver, Copyright IBM Corp. 2018");
>  MODULE_LICENSE("GPL v2");
> +MODULE_VERSION(VFIO_AP_MODULE_VERSION);
>  
>  static struct ap_driver vfio_ap_drv;
>  

Setting a version manually has some drawbacks:
- tools wanting to check for capabilities need to keep track which
  versions support which features
- you need to remember to actually bump the version when adding a new,
  visible feature
(- selective downstream backports may get into a pickle, but that's
arguably not your problem)

Is there no way for a tool to figure out whether this is supported?
E.g., via existence of a sysfs file, or via a known error that will
occur. If not, it's maybe better to expose known capabilities via a
generic interface.