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Date:   Wed, 22 Sep 2021 20:01:16 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Alex Williamson <alex.williamson@redhat.com>
Cc:     Liu Yi L <yi.l.liu@intel.com>, hch@lst.de, jasowang@redhat.com,
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Subject: Re: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND_IOMMUFD
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On Wed, Sep 22, 2021 at 03:01:01PM -0600, Alex Williamson wrote:
> On Tue, 21 Sep 2021 14:29:39 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Sun, Sep 19, 2021 at 02:38:36PM +0800, Liu Yi L wrote:
> > > +struct vfio_device_iommu_bind_data {
> > > +	__u32	argsz;
> > > +	__u32	flags;
> > > +	__s32	iommu_fd;
> > > +	__u64	dev_cookie;  
> > 
> > Missing explicit padding
> > 
> > Always use __aligned_u64 in uapi headers, fix all the patches.
> 
> We don't need padding or explicit alignment if we just swap the order
> of iommu_fd and dev_cookie.  Thanks,

Yes, the padding should all be checked and minimized

But it is always good practice to always use __aligned_u64 in the uapi
headers just in case someone messes it up someday - it prevents small
mistakes from becoming an ABI mess.

Jason