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+Name
+
+ EXT_device_persistent_id
+
+Name Strings
+
+ EGL_EXT_device_persistent_id
+
+Contributors
+
+ Kyle Brenneman, NVIDIA (kbrenneman 'at' nvidia.com)
+
+Contact
+
+ Kyle Brenneman, NVIDIA (kbrenneman 'at' nvidia.com)
+
+Version
+
+ Version 1 - April 19, 2021
+
+Number
+
+ EGL Extension #142
+
+Extension Type
+
+ EGL device extension
+
+Dependencies
+
+ Written based on the wording of the EGL 1.5 specification.
+
+ EGL_EXT_device_query is required.
+
+Overview
+
+ Applications can query a list of EGLDeviceEXT handles, but those
+ handles are only valid within the process that queried them. An
+ application has no way, for example, to record its selection and
+ select the same device when run again later.
+
+ This extension provides a vendor name and a set of UUID's, which
+ provide a unique, persistent identifier for EGLDeviceEXT handles.
+ This allows applications to find the EGLDeviceEXT for the same
+ device across multiple processes, and across multiple APIs.
+
+New Procedures and Functions
+
+ EGLBoolean eglQueryDeviceBinaryEXT(EGLDeviceEXT device,
+ EGLint name,
+ EGLint max_size,
+ void *value,
+ EGLint *size);
+
+New Tokens
+
+ Accepted by the <name> parameter of eglQueryDeviceStringEXT:
+
+ EGL_DRIVER_NAME_EXT 0x335E
+
+ Accepted by the <name> parameter of eglQueryDeviceBinaryEXT:
+
+ EGL_DEVICE_UUID_EXT 0x335C
+ EGL_DRIVER_UUID_EXT 0x335D
+
+Changes to section 3.2 (Devices)
+
+ Add the following paragraph to the description of
+ eglQueryDeviceStringEXT:
+
+ EGL_DRIVER_NAME_EXT returns a string which identifies the driver
+ that controls the device. This string remains persistent across
+ multiple versions of a driver, and an application can use strcmp(3)
+ to compare the strings for equality. Otherwise, the contents are
+ implementation-defined.
+
+
+ Add to the end of section 3.2:
+
+ To query a binary attribute for a device, use:
+
+ EGLBoolean eglQueryDeviceBinaryEXT(EGLDeviceEXT device,
+ EGLint name,
+ EGLint max_size,
+ void *value,
+ EGLint *size);
+
+ On success, EGL_TRUE is returned. If <value> is NULL, then
+ <max_size> is ignored, and the size of the attribute in bytes is
+ returned in <size>.
+
+ On failure, EGL_FALSE is returned. An EGL_BAD_ATTRIBUTE error is
+ generated if <name> is not a valid attribute. An EGL_BAD_DEVICE_EXT
+ error is generated if <device> is not a valid EGLDeviceEXT.
+
+ If <value> is not NULL, then the attribute value is returned in
+ <value>. At most <max_size> bytes are written. <size> returns the
+ number of bytes that were actually written.
+
+ Note that the EGL_DEVICE_UUID_EXT and EGL_DRIVER_UUID_EXT attributes
+ are always 16-byte values, and so the application can simply use a
+ 16-byte buffer without needing to query the size beforehand. Future
+ extensions may add variable-length attributes.
+
+
+ EGL_DEVICE_UUID_EXT is a UUID that identifies a physical device,
+ returned as a 16-byte binary value. The device UUID uniquely
+ identifies a physical device, and is persistent across reboots,
+ processes, APIs, and (to the extent possible) driver versions.
+
+ EGL_DEVICE_UUID_EXT may or may not be persistent across changes in
+ hardware configuration. Similarly, it is not guaranteed to be unique
+ or persistent across different (physical or virtual) computers.
+
+ Note that EGL_DEVICE_UUID_EXT alone is not guaranteed to be unique
+ across all EGLDeviceEXT handles. If an EGL implementation supports
+ multiple drivers, and two drivers can use the same physical device,
+ then there will be a separate EGLDeviceEXT handle from each driver.
+ Both EGLDeviceEXT handles may use the same device UUID.
+
+ In that case, an application must use EGL_DRIVER_NAME_EXT or
+ EGL_DRIVER_UUID_EXT to distinguish between the two EGLDeviceEXT
+ handles.
+
+
+ EGL_DRIVER_UUID_EXT is a UUID that identifies a driver build
+ in use for a device. The driver UUID is persistent across reboots,
+ processes, and APIs, but is not persistent across driver versions.
+
+Issues
+
+ 1. Should we use UUID's or strings to identify devices?
+
+ RESOLVED: Use UUID's for devices, plus a vendor name string to
+ disambiguate devices that are supported by multiple drivers.
+
+ A device UUID and driver UUID allow an application to correlate
+ an EGLDeviceEXT with the same device in other APIs, such as a
+ VkPhysicalDevice in Vulkan.
+
+ A UUID does not impose any additional requirements on an EGL
+ implementation compared to a string: If an EGL implementation
+ could generate a string identifier, then the implementation can
+ simply hash that string to generate a UUID value.
+
+ 2. Can two EGLDeviceEXT handles have the same EGL_DEVICE_UUID_EXT?
+
+ RESOLVED: Yes, if they correspond to the same physical device.
+
+ The semantics of the device and driver UUID's are inherited from
+ Vulkan, which only requires that a device UUID be unique to a
+ physical device, not unique across VkPhysicalDevice handles.
+
+ 3. Do we need the EGL_DRIVER_NAME_EXT string?
+
+ RESOLVED: Yes, because the EGL_DEVICE_UUID_EXT alone is not
+ unique, and EGL_DRIVER_UUID_EXT is not persistent.
+
+ A (EGL_DRIVER_NAME_EXT, EGL_DEVICE_UUID_EXT) pair provides a
+ unique, persistent identifier.
+
+ In addition, on systems that use libglvnd, applications could
+ use EGL_DRIVER_NAME_EXT to match the vendor names from
+ GLX_EXT_libglvnd.
+
+ 4. What happens if an application stores a device UUID, and the
+ hardware configuration or driver version changes?
+
+ RESOLVED: The device UUID may become invalid, and the
+ application should select a new device.
+
+ If a device is removed from a system, then there will be no
+ EGLDeviceEXT handle for it, and thus no device UUID for it.
+
+ Similarly, if a device is moved within a system (e.g., plugged
+ into a different PCI slot), then a driver may not be able to
+ identify it as the same device, and so the device might get a
+ different UUID.
+
+ While not a requirement, drivers should still try to keep device
+ UUID's persistent whenever possible, to avoid invalidating
+ config files. Similarly, if a device is removed or replaced,
+ then a driver should try to ensure that the same device UUID
+ does not refer to a different device.
+
+ As an example, a driver could derive a UUID based on a PCI
+ vendor and device number, plus the PCI domain, bus, slot, and
+ function numbers:
+
+ * The PCI device number ensures that replacing a GPU with a
+ different model in the same PCI slot produces a different
+ device UUID string.
+ * Using the PCI bus numbers ensures that two identical
+ GPU's in the same system have unique UUID's.
+ * The whole tuple can easily stay persistent across driver
+ versions.
+
+Revision History
+
+ #1 (April 19, 2021) Kyle Brenneman
+
+ - Initial draft