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Date:   Fri, 16 Apr 2021 14:54:38 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc:     Alex Williamson <alex.williamson@redhat.com>,
        Auger Eric <eric.auger@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "cgroups@vger.kernel.org" <cgroups@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs
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On Fri, Apr 16, 2021 at 10:23:32AM -0700, Jacob Pan wrote:

> Perhaps similar to cgroup v1 vs v2, it took a long time and with known
> limitations in v1.

cgroup v2 is still having transition problems, if anything it is a
cautionary tale to think really hard about uAPI because transitioning
can be really hard.

It might be very wise to make /dev/ioasid and /dev/vfio ioctl
compatible in some way so existing software has a smoother upgrade
path.

For instance by defining a default IOASID

Jason