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(dynamic-2a02-3100-9c83-d900-3892-32a1-3274-3aec.310.pool.telefonica.de. [2a02:3100:9c83:d900:3892:32a1:3274:3aec]) by smtp.googlemail.com with ESMTPSA id a640c23a62f3a-aa625e4da84sm197172566b.4.2024.12.05.23.35.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Dec 2024 23:35:48 -0800 (PST) Message-ID: <9015ce52-e4f3-459c-bd74-b8707cf8fd88@gmail.com> Date: Fri, 6 Dec 2024 08:35:47 +0100 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] vfio/mdev: inline needed class_compat functionality To: Alex Williamson , Greg Kroah-Hartman Cc: "Rafael J. Wysocki" , Kirti Wankhede , kvm@vger.kernel.org References: <147a2a3e-8227-4f1b-9ab4-d0b4f261d2a6@gmail.com> <0a14a4df-fbb5-4613-837f-f8025dc73380@gmail.com> <2024120430-boneless-wafer-bf0c@gregkh> <2024120410-promoter-blandness-efa1@gregkh> <20241204123040.7e3483a4.alex.williamson@redhat.com> Content-Language: en-US From: Heiner Kallweit Autocrypt: addr=hkallweit1@gmail.com; keydata= xsFNBF/0ZFUBEAC0eZyktSE7ZNO1SFXL6cQ4i4g6Ah3mOUIXSB4pCY5kQ6OLKHh0FlOD5/5/ sY7IoIouzOjyFdFPnz4Bl3927ClT567hUJJ+SNaFEiJ9vadI6vZm2gcY4ExdIevYHWe1msJF MVE4yNwdS+UsPeCF/6CQQTzHc+n7DomE7fjJD5J1hOJjqz2XWe71fTvYXzxCFLwXXbBiqDC9 dNqOe5odPsa4TsWZ09T33g5n2nzTJs4Zw8fCy8rLqix/raVsqr8fw5qM66MVtdmEljFaJ9N8 /W56qGCp+H8Igk/F7CjlbWXiOlKHA25mPTmbVp7VlFsvsmMokr/imQr+0nXtmvYVaKEUwY2g 86IU6RAOuA8E0J5bD/BeyZdMyVEtX1kT404UJZekFytJZrDZetwxM/cAH+1fMx4z751WJmxQ J7mIXSPuDfeJhRDt9sGM6aRVfXbZt+wBogxyXepmnlv9K4A13z9DVLdKLrYUiu9/5QEl6fgI kPaXlAZmJsQfoKbmPqCHVRYj1lpQtDM/2/BO6gHASflWUHzwmBVZbS/XRs64uJO8CB3+V3fa cIivllReueGCMsHh6/8wgPAyopXOWOxbLsZ291fmZqIR0L5Y6b2HvdFN1Xhc+YrQ8TKK+Z4R mJRDh0wNQ8Gm89g92/YkHji4jIWlp2fwzCcx5+lZCQ1XdqAiHQARAQABzSZIZWluZXIgS2Fs bHdlaXQgPGhrYWxsd2VpdDFAZ21haWwuY29tPsLBjgQTAQgAOBYhBGxfqY/yOyXjyjJehXLe ig9U8DoMBQJf9GRVAhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEHLeig9U8DoMSycQ AJbfg8HZEK0ljV4M8nvdaiNixWAufrcZ+SD8zhbxl8GispK4F3Yo+20Y3UoZ7FcIidJWUUJL axAOkpI/70YNhlqAPMsuudlAieeYZKjIv1WV5ucNZ3VJ7dC+dlVqQdAr1iD869FZXvy91KhJ wYulyCf+s4T9YgmLC6jLMBZghKIf1uhSd0NzjyCqYWbk2ZxByZHgunEShOhHPHswu3Am0ftt ePaYIHgZs+Vzwfjs8I7EuW/5/f5G9w1vibXxtGY/GXwgGGHRDjFM7RSprGOv4F5eMGh+NFUJ TU9N96PQYMwXVxnQfRXl8O6ffSVmFx4H9rovxWPKobLmqQL0WKLLVvA/aOHCcMKgfyKRcLah 57vGC50Ga8oT2K1g0AhKGkyJo7lGXkMu5yEs0m9O+btqAB261/E3DRxfI1P/tvDZpLJKtq35 dXsj6sjvhgX7VxXhY1wE54uqLLHY3UZQlmH3QF5t80MS7/KhxB1pO1Cpcmkt9hgyzH8+5org +9wWxGUtJWNP7CppY+qvv3SZtKJMKsxqk5coBGwNkMms56z4qfJm2PUtJQGjA65XWdzQACib 2iaDQoBqGZfXRdPT0tC1H5kUJuOX4ll1hI/HBMEFCcO8++Bl2wcrUsAxLzGvhINVJX2DAQaF aNetToazkCnzubKfBOyiTqFJ0b63c5dqziAgzsFNBF/0ZFUBEADF8UEZmKDl1w/UxvjeyAeX kghYkY3bkK6gcIYXdLRfJw12GbvMioSguvVzASVHG8h7NbNjk1yur6AONfbUpXKSNZ0skV8V fG+ppbaY+zQofsSMoj5gP0amwbwvPzVqZCYJai81VobefTX2MZM2Mg/ThBVtGyzV3NeCpnBa 8AX3s9rrX2XUoCibYotbbxx9afZYUFyflOc7kEpc9uJXIdaxS2Z6MnYLHsyVjiU6tzKCiVOU KJevqvzPXJmy0xaOVf7mhFSNQyJTrZpLa+tvB1DQRS08CqYtIMxRrVtC0t0LFeQGly6bOngr ircurWJiJKbSXVstLHgWYiq3/GmCSx/82ObeLO3PftklpRj8d+kFbrvrqBgjWtMH4WtK5uN5 1WJ71hWJfNchKRlaJ3GWy8KolCAoGsQMovn/ZEXxrGs1ndafu47yXOpuDAozoHTBGvuSXSZo ythk/0EAuz5IkwkhYBT1MGIAvNSn9ivE5aRnBazugy0rTRkVggHvt3/7flFHlGVGpBHxFUwb /a4UjJBPtIwa4tWR8B1Ma36S8Jk456k2n1id7M0LQ+eqstmp6Y+UB+pt9NX6t0Slw1NCdYTW gJezWTVKF7pmTdXszXGxlc9kTrVUz04PqPjnYbv5UWuDd2eyzGjrrFOsJEi8OK2d2j4FfF++ AzOMdW09JVqejQARAQABwsF2BBgBCAAgFiEEbF+pj/I7JePKMl6Fct6KD1TwOgwFAl/0ZFUC GwwACgkQct6KD1TwOgxUfg//eAoYc0Vm4NrxymfcY30UjHVD0LgSvU8kUmXxil3qhFPS7KA+ y7tgcKLHOkZkXMX5MLFcS9+SmrAjSBBV8omKoHNo+kfFx/dUAtz0lot8wNGmWb+NcHeKM1eb nwUMOEa1uDdfZeKef/U/2uHBceY7Gc6zPZPWgXghEyQMTH2UhLgeam8yglyO+A6RXCh+s6ak Wje7Vo1wGK4eYxp6pwMPJXLMsI0ii/2k3YPEJPv+yJf90MbYyQSbkTwZhrsokjQEaIfjrIk3 rQRjTve/J62WIO28IbY/mENuGgWehRlTAbhC4BLTZ5uYS0YMQCR7v9UGMWdNWXFyrOB6PjSu Trn9MsPoUc8qI72mVpxEXQDLlrd2ijEWm7Nrf52YMD7hL6rXXuis7R6zY8WnnBhW0uCfhajx q+KuARXC0sDLztcjaS3ayXonpoCPZep2Bd5xqE4Ln8/COCslP7E92W1uf1EcdXXIrx1acg21 H/0Z53okMykVs3a8tECPHIxnre2UxKdTbCEkjkR4V6JyplTS47oWMw3zyI7zkaadfzVFBxk2 lo/Tny+FX1Azea3Ce7oOnRUEZtWSsUidtIjmL8YUQFZYm+JUIgfRmSpMFq8JP4VH43GXpB/S OCrl+/xujzvoUBFV/cHKjEQYBxo+MaiQa1U54ykM2W4DnHb1UiEf5xDkFd4= In-Reply-To: <20241204123040.7e3483a4.alex.williamson@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 04.12.2024 20:30, Alex Williamson wrote: > On Wed, 4 Dec 2024 19:16:03 +0100 > Greg Kroah-Hartman wrote: > >> On Wed, Dec 04, 2024 at 06:01:36PM +0100, Heiner Kallweit wrote: >>> On 04.12.2024 10:32, Greg Kroah-Hartman wrote: >>>> On Tue, Dec 03, 2024 at 09:11:47PM +0100, Heiner Kallweit wrote: >>>>> vfio/mdev is the last user of class_compat, and it doesn't use it for >>>>> the intended purpose. See kdoc of class_compat_register(): >>>>> Compatibility class are meant as a temporary user-space compatibility >>>>> workaround when converting a family of class devices to a bus devices. >>>> >>>> True, so waht is mdev doing here? >>>> >>>>> In addition it uses only a part of the class_compat functionality. >>>>> So inline the needed functionality, and afterwards all class_compat >>>>> code can be removed. >>>>> >>>>> No functional change intended. Compile-tested only. >>>>> >>>>> Signed-off-by: Heiner Kallweit >>>>> --- >>>>> drivers/vfio/mdev/mdev_core.c | 12 ++++++------ >>>>> 1 file changed, 6 insertions(+), 6 deletions(-) >>>>> >>>>> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c >>>>> index ed4737de4..a22c49804 100644 >>>>> --- a/drivers/vfio/mdev/mdev_core.c >>>>> +++ b/drivers/vfio/mdev/mdev_core.c >>>>> @@ -18,7 +18,7 @@ >>>>> #define DRIVER_AUTHOR "NVIDIA Corporation" >>>>> #define DRIVER_DESC "Mediated device Core Driver" >>>>> >>>>> -static struct class_compat *mdev_bus_compat_class; >>>>> +static struct kobject *mdev_bus_kobj; >>>> >>>> >>>> >>>>> >>>>> static LIST_HEAD(mdev_list); >>>>> static DEFINE_MUTEX(mdev_list_lock); >>>>> @@ -76,7 +76,7 @@ int mdev_register_parent(struct mdev_parent *parent, struct device *dev, >>>>> if (ret) >>>>> return ret; >>>>> >>>>> - ret = class_compat_create_link(mdev_bus_compat_class, dev, NULL); >>>>> + ret = sysfs_create_link(mdev_bus_kobj, &dev->kobj, dev_name(dev)); >>>> >>>> This feels really wrong, why create a link to a random kobject? Who is >>>> using this kobject link? >>>> >>>>> if (ret) >>>>> dev_warn(dev, "Failed to create compatibility class link\n"); >>>>> >>>>> @@ -98,7 +98,7 @@ void mdev_unregister_parent(struct mdev_parent *parent) >>>>> dev_info(parent->dev, "MDEV: Unregistering\n"); >>>>> >>>>> down_write(&parent->unreg_sem); >>>>> - class_compat_remove_link(mdev_bus_compat_class, parent->dev, NULL); >>>>> + sysfs_remove_link(mdev_bus_kobj, dev_name(parent->dev)); >>>>> device_for_each_child(parent->dev, NULL, mdev_device_remove_cb); >>>>> parent_remove_sysfs_files(parent); >>>>> up_write(&parent->unreg_sem); >>>>> @@ -251,8 +251,8 @@ static int __init mdev_init(void) >>>>> if (ret) >>>>> return ret; >>>>> >>>>> - mdev_bus_compat_class = class_compat_register("mdev_bus"); >>>>> - if (!mdev_bus_compat_class) { >>>>> + mdev_bus_kobj = class_pseudo_register("mdev_bus"); >>>> >>>> But this isn't a class, so let's not fake it please. Let's fix this >>>> properly, odds are all of this code can just be removed entirely, right? >>>> >>> >>> After I removed class_compat from i2c core, I asked Alex basically the >>> same thing: whether class_compat support can be removed from vfio/mdev too. >>> >>> His reply: >>> I'm afraid we have active userspace tools dependent on >>> /sys/class/mdev_bus currently, libvirt for one. We link mdev parent >>> devices here and I believe it's the only way for userspace to find >>> those parent devices registered for creating mdev devices. If there's a >>> desire to remove class_compat, we might need to add some mdev >>> infrastructure to register the class ourselves to maintain the parent >>> links. >>> >>> >>> It's my understanding that /sys/class/mdev_bus has nothing in common >>> with an actual class, it's just a container for devices which at least >>> partially belong to other classes. And there's user space tools depending >>> on this structure. >> >> That's odd, when this was added, why was it added this way? The >> class_compat stuff is for when classes move around, yet this was always >> done in this way? >> >> And what tools use this symlink today that can't be updated? > > It's been this way for 8 years, so it's hard to remember exact > motivation for using this mechanism, whether we just didn't look hard > enough at the class_compat or it didn't pass by the right set of eyes. > Yes, it's always been this way for the mdev_bus class. > > The intention here is much like other classes, that we have a node in > sysfs where we can find devices that provide a common feature, in this > case providing support for creating and managing vfio mediated devices > (mdevs). The perhaps unique part of this use case is that these devices > aren't strictly mdev providers, they might also belong to another class > and the mdev aspect of their behavior might be dynamically added after > the device itself is added. > > I've done some testing with this series and it does indeed seem to > maintain compatibility with existing userspace tools, mdevctl and > libvirt. We can update these tools, but then we get into the breaking Greg, is this testing, done by Alex, sufficient for you to take the series? > userspace and deprecation period questions, where we may further delay > removal of class_compat. Also if we were to re-implement this, is there > a better mechanism than proposed here within the class hierarchy, or > would you recommend a non-class approach? Thanks, > You have /sys/bus/mdev. Couldn't we create a directory here which holds the links to the devices in question? Then user space would simply have to switch from /sys/class/mdev_bus to /sys/bus/mdev/. > Alex > Heiner