Re: [PATCH 4/8] vfio: Remove #ifdefs around CONFIG_VFIO_NOIOMMU

From: Jason Gunthorpe <jgg@nvidia.com>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH 4/8] vfio: Remove #ifdefs around CONFIG_VFIO_NOIOMMU
Date: Wed, 31 Aug 2022 12:28:51 -0300	[thread overview]
Message-ID: <Yw9+M7qWo8aLMpb6@nvidia.com> (raw)
In-Reply-To: <BN9PR11MB5276255A50937E1D2C3590B88C789@BN9PR11MB5276.namprd11.prod.outlook.com>

On Wed, Aug 31, 2022 at 08:48:55AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Wednesday, August 31, 2022 9:02 AM
> >  #ifdef CONFIG_VFIO_NOIOMMU
> > -static bool noiommu __read_mostly;
> > +static bool vfio_noiommu __read_mostly;
> >  module_param_named(enable_unsafe_noiommu_mode,
> > -		   noiommu, bool, S_IRUGO | S_IWUSR);
> > +		   vfio_noiommu, bool, S_IRUGO | S_IWUSR);
> >  MODULE_PARM_DESC(enable_unsafe_noiommu_mode, "Enable UNSAFE,
> > no-IOMMU mode.  This mode provides no device isolation, no DMA
> > translation, no host kernel protection, cannot be used for device assignment
> > to virtual machines, requires RAWIO permissions, and will taint the kernel.  If
> > you do not know what this is for, step away. (default: false)");
> > +#else
> > +enum { vfio_noiommu = false };
> >  #endif
> 
> what is the benefit of enum here?

It means we don't have to use #ifdef to protect references to
vfio_noiommu. Do mean enum vs #define? I prefer generally prefer enums
as they behave more like a variable.

Jason