egl: implement interfaces for EGL_EXT_device_drm

This extension (together with the optional `EGL_EXT_device_drm_render_node` extension) allows querying the DRM primary and render device node filenames from `EGLDevice`, to help associating them with DRM devices. Additionally a platform display _can_ be created with a DRM file descriptor with master permissions, but this is only useful in situations where EGL might fail to open a file descriptor itself or will fail to acquire master permissions (which are only required when the implementation needs to "modify output attributes": but no behaviour is defined by this extension that requires this). This file descriptor will be duplicated by the implementation if it needs to use it beyond the call to `eglGetPlatformDisplayEXT()`, and does not need to be kept alive by the caller. Note that `EGL_EXT_output_drm` is omitted for now, because it relies on the equally unimplemented `EGL_EXT_output_base` extension.
rust-windowing · Sep 10, 2024 · d8742b6 · d8742b6
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,9 +1,11 @@
 # Unreleased
 
-- Fixed EGL's `Device::query_devices()` being too strict about required extensions
-- Fixed crash in `EglGetProcAddress` on Win32-x86 platform due to wrong calling convention
-- Fixed EGL's `Display::device()` always returning an error due to invalid pointer-argument passing inside
+- Fixed EGL's `Device::query_devices()` being too strict about required extensions.
+- Fixed crash in `EglGetProcAddress` on Win32-x86 platform due to wrong calling convention.
+- Fixed EGL's `Display::device()` always returning an error due to invalid pointer-argument passing inside.
 - Fixed EGL's `Display::new()` making an `EGLDisplay::Khr` when the EGL version for the display is 1.4 or lower.
+- Added `Device::drm_device_node_path()` and `Device::drm_render_device_node_path()` getters to EGL via `EGL_EXT_device_drm`.
+- Added support for `DrmDisplayHandle` in EGL's `Display::with_device()` using `EGL_DRM_MASTER_FD_EXT` from `EGL_EXT_device_drm`.
 
 # Version 0.32.0
 

diff --git a/glutin/src/api/egl/device.rs b/glutin/src/api/egl/device.rs
@@ -1,7 +1,8 @@
 //! Everything related to `EGLDevice`.
 
 use std::collections::HashSet;
-use std::ffi::{c_void, CStr};
+use std::ffi::CStr;
+use std::path::Path;
 use std::ptr;
 
 use glutin_egl_sys::egl;
@@ -17,10 +18,15 @@ use super::{Egl, EGL};
 pub struct Device {
     inner: EGLDeviceEXT,
     extensions: HashSet<&'static str>,
-    name: Option<String>,
-    vendor: Option<String>,
+    name: Option<&'static str>,
+    vendor: Option<&'static str>,
 }
 
+// SAFETY: An EGLDevice is immutable and valid for the lifetime of the EGL
+// library.
+unsafe impl Send for Device {}
+unsafe impl Sync for Device {}
+
 impl Device {
     /// Query the available devices.
     ///
@@ -93,39 +99,87 @@ impl Device {
     ///
     /// These extensions are distinct from the display extensions and should not
     /// be used interchangeably.
-    pub fn extensions(&self) -> &HashSet<&str> {
+    pub fn extensions(&self) -> &HashSet<&'static str> {
         &self.extensions
     }
 
     /// Get the name of the device.
     ///
     /// This function will return [`None`] if the `EGL_EXT_device_query_name`
     /// device extension is not available.
-    pub fn name(&self) -> Option<&str> {
-        self.name.as_deref()
+    pub fn name(&self) -> Option<&'static str> {
+        self.name
     }
 
     /// Get the vendor of the device.
     ///
     /// This function will return [`None`] if the `EGL_EXT_device_query_name`
     /// device extension is not available.
-    pub fn vendor(&self) -> Option<&str> {
-        self.vendor.as_deref()
+    pub fn vendor(&self) -> Option<&'static str> {
+        self.vendor
     }
 
     /// Get a raw handle to the `EGLDevice`.
-    pub fn raw_device(&self) -> *const c_void {
+    pub fn raw_device(&self) -> EGLDeviceEXT {
         self.inner
     }
-}
 
-// SAFETY: An EGLDevice is immutable and valid for the lifetime of the EGL
-// library.
-unsafe impl Send for Device {}
-unsafe impl Sync for Device {}
+    /// Get the DRM primary or render device node path for this
+    /// [`EGLDeviceEXT`].
+    ///
+    /// Requires the [`EGL_EXT_device_drm`] extension.
+    ///
+    /// If the [`EGL_EXT_device_drm_render_node`] extension is supported, this
+    /// is guaranteed to return the **primary** device node path, or [`None`].
+    /// Consult [`Self::drm_render_device_node_path()`] to retrieve the
+    /// **render** device node path.
+    ///
+    /// [`EGL_EXT_device_drm`]: https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_device_drm.txt
+    /// [`EGL_EXT_device_drm_render_node`]: https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_device_drm_render_node.txt
+    pub fn drm_device_node_path(&self) -> Option<&'static Path> {
+        if !self.extensions.contains("EGL_EXT_device_drm") {
+            return None;
+        }
 
-impl Device {
-    unsafe fn query_string(egl_device: *const c_void, name: egl::types::EGLenum) -> Option<String> {
+        // SAFETY: We pass a valid EGLDevice pointer, and validated that the enum name
+        // is valid because the extension is present.
+        unsafe { Self::query_string(self.raw_device(), egl::DRM_DEVICE_FILE_EXT) }.map(Path::new)
+    }
+
+    /// Get the DRM render device node path for this [`EGLDeviceEXT`].
+    ///
+    /// Requires the [`EGL_EXT_device_drm_render_node`] extension.
+    ///
+    /// If the [`EGL_EXT_device_drm`] extension is supported in addition to
+    /// [`EGL_EXT_device_drm_render_node`],
+    /// consult [`Self::drm_device_node_path()`] to retrieve the **primary**
+    /// device node path.
+    ///
+    /// [`EGL_EXT_device_drm`]: https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_device_drm.txt
+    /// [`EGL_EXT_device_drm_render_node`]: https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_device_drm_render_node.txt
+    pub fn drm_render_device_node_path(&self) -> Option<&'static Path> {
+        if !self.extensions.contains("EGL_EXT_device_drm_render_node") {
+            return None;
+        }
+
+        const EGL_DRM_RENDER_NODE_PATH_EXT: egl::types::EGLenum = 0x3377;
+        // SAFETY: We pass a valid EGLDevice pointer, and validated that the enum name
+        // is valid because the extension is present.
+        unsafe { Self::query_string(self.raw_device(), EGL_DRM_RENDER_NODE_PATH_EXT) }
+            .map(Path::new)
+    }
+
+    /// # Safety
+    /// The caller must pass  a valid `egl_device` pointer and must ensure that
+    /// `name` is valid for this device, i.e. by guaranteeing that the
+    /// extension that introduces it is present.
+    ///
+    /// The returned string is `'static` for the lifetime of the globally loaded
+    /// EGL library in [`EGL`].
+    unsafe fn query_string(
+        egl_device: EGLDeviceEXT,
+        name: egl::types::EGLenum,
+    ) -> Option<&'static str> {
         let egl = super::EGL.as_ref().unwrap();
 
         // SAFETY: The caller has ensured the name is valid.
@@ -135,10 +189,10 @@ impl Device {
             return None;
         }
 
-        unsafe { CStr::from_ptr(ptr) }.to_str().ok().map(String::from)
+        unsafe { CStr::from_ptr(ptr) }.to_str().ok()
     }
 
-    pub(crate) fn from_ptr(egl: &Egl, ptr: *const c_void) -> Result<Self> {
+    pub(crate) fn from_ptr(egl: &Egl, ptr: EGLDeviceEXT) -> Result<Self> {
         // SAFETY: The EGL specification guarantees the returned string is
         // static and null terminated:
         //

diff --git a/glutin/src/api/egl/display.rs b/glutin/src/api/egl/display.rs
@@ -13,9 +13,7 @@ use glutin_egl_sys::egl::types::{EGLAttrib, EGLDisplay, EGLint};
 
 use once_cell::sync::OnceCell;
 
-use raw_window_handle::RawDisplayHandle;
-#[cfg(x11_platform)]
-use raw_window_handle::XlibDisplayHandle;
+use raw_window_handle::{RawDisplayHandle, XlibDisplayHandle};
 
 use crate::config::ConfigTemplate;
 use crate::context::Version;
@@ -91,8 +89,10 @@ impl Display {
     ///
     /// # Safety
     ///
-    /// If `raw_display` is [`Some`], `raw_display` must point to a valid system
-    /// display.
+    /// If `raw_display` is [`Some`], `raw_display` must point to a valid
+    /// [`RawDisplayHandle::Drm`]. The provided
+    /// [`raw_display_handle::DrmDisplayHandle.fd`] may be closed after calling
+    /// this function.
     pub unsafe fn with_device(
         device: &Device,
         raw_display: Option<RawDisplayHandle>,
@@ -102,13 +102,6 @@ impl Display {
             None => return Err(ErrorKind::NotFound.into()),
         };
 
-        if raw_display.is_some() {
-            return Err(ErrorKind::NotSupported(
-                "Display::with_device does not support a `raw_display` argument yet",
-            )
-            .into());
-        }
-
         if !egl.GetPlatformDisplayEXT.is_loaded() {
             return Err(ErrorKind::NotSupported("eglGetPlatformDisplayEXT is not supported").into());
         }
@@ -129,9 +122,22 @@ impl Display {
 
         let mut attrs = Vec::<EGLint>::with_capacity(3);
 
-        // TODO: Some extensions exist like EGL_EXT_device_drm which allow specifying
-        // which DRM master fd to use under the hood by the implementation. This would
-        // mean there would need to be an unsafe equivalent to this function.
+        match raw_display {
+            Some(RawDisplayHandle::Drm(handle))
+                if device.extensions().contains("EGL_EXT_device_drm") =>
+            {
+                attrs.push(egl::DRM_MASTER_FD_EXT as EGLint);
+                attrs.push(handle.fd as EGLint);
+            },
+            Some(_) => {
+                return Err(ErrorKind::NotSupported(
+                    "`egl::display::Display::with_device()` does not support \
+                     non-`DrmDisplayHandle` `RawDisplayHandle`s",
+                )
+                .into())
+            },
+            None => {},
+        };
 
         // Push at the end so we can pop it on failure
         let mut has_display_reference = extensions.contains("EGL_KHR_display_reference");
@@ -254,13 +260,11 @@ impl Display {
 
         let mut attrs = Vec::<EGLAttrib>::with_capacity(5);
         let (platform, display) = match display {
-            #[cfg(wayland_platform)]
             RawDisplayHandle::Wayland(handle)
                 if extensions.contains("EGL_KHR_platform_wayland") =>
             {
                 (egl::PLATFORM_WAYLAND_KHR, handle.display.as_ptr())
             },
-            #[cfg(x11_platform)]
             RawDisplayHandle::Xlib(handle) if extensions.contains("EGL_KHR_platform_x11") => {
                 attrs.push(egl::PLATFORM_X11_SCREEN_KHR as EGLAttrib);
                 attrs.push(handle.screen as EGLAttrib);
@@ -272,6 +276,12 @@ impl Display {
             RawDisplayHandle::Gbm(handle) if extensions.contains("EGL_KHR_platform_gbm") => {
                 (egl::PLATFORM_GBM_KHR, handle.gbm_device.as_ptr())
             },
+            RawDisplayHandle::Drm(_) => {
+                return Err(ErrorKind::NotSupported(
+                    "`DrmDisplayHandle` must be used with `egl::display::Display::with_device()`",
+                )
+                .into())
+            },
             RawDisplayHandle::Android(_) if extensions.contains("EGL_KHR_platform_android") => {
                 (egl::PLATFORM_ANDROID_KHR, egl::DEFAULT_DISPLAY as *mut _)
             },
@@ -328,13 +338,11 @@ impl Display {
         let mut attrs = Vec::<EGLint>::with_capacity(5);
         let mut legacy = false;
         let (platform, display) = match display {
-            #[cfg(wayland_platform)]
             RawDisplayHandle::Wayland(handle)
                 if extensions.contains("EGL_EXT_platform_wayland") =>
             {
                 (egl::PLATFORM_WAYLAND_EXT, handle.display.as_ptr())
             },
-            #[cfg(x11_platform)]
             RawDisplayHandle::Xlib(handle) if extensions.contains("EGL_EXT_platform_x11") => {
                 attrs.push(egl::PLATFORM_X11_SCREEN_EXT as EGLint);
                 attrs.push(handle.screen as EGLint);
@@ -343,7 +351,6 @@ impl Display {
                     handle.display.map_or(egl::DEFAULT_DISPLAY as *mut _, |d| d.as_ptr()),
                 )
             },
-            #[cfg(x11_platform)]
             RawDisplayHandle::Xcb(handle)
                 if extensions.contains("EGL_MESA_platform_xcb")
                     || extensions.contains("EGL_EXT_platform_xcb") =>
@@ -358,6 +365,12 @@ impl Display {
             RawDisplayHandle::Gbm(handle) if extensions.contains("EGL_MESA_platform_gbm") => {
                 (egl::PLATFORM_GBM_MESA, handle.gbm_device.as_ptr())
             },
+            RawDisplayHandle::Drm(_) => {
+                return Err(ErrorKind::NotSupported(
+                    "`DrmDisplayHandle` must be used with `egl::display::Display::with_device()`",
+                )
+                .into())
+            },
             RawDisplayHandle::Windows(..) if extensions.contains("EGL_ANGLE_platform_angle") => {
                 // Only CreateWindowSurface appears to work with Angle.
                 legacy = true;
@@ -419,7 +432,12 @@ impl Display {
     fn get_display(egl: &Egl, display: RawDisplayHandle) -> Result<EglDisplay> {
         let display = match display {
             RawDisplayHandle::Gbm(handle) => handle.gbm_device.as_ptr(),
-            #[cfg(x11_platform)]
+            RawDisplayHandle::Drm(_) => {
+                return Err(ErrorKind::NotSupported(
+                    "`DrmDisplayHandle` must be used with `egl::display::Display::with_device()`",
+                )
+                .into())
+            },
             RawDisplayHandle::Xlib(XlibDisplayHandle { display, .. }) => {
                 display.map_or(egl::DEFAULT_DISPLAY as *mut _, |d| d.as_ptr())
             },

diff --git a/glutin/src/api/egl/mod.rs b/glutin/src/api/egl/mod.rs
@@ -28,6 +28,9 @@ pub mod device;
 pub mod display;
 pub mod surface;
 
+// WARNING: If this implementation is ever changed to unload or replace the
+// library, note that public API functions currently retirm `&'static str`ings
+// out of it, which would become invalid.
 pub(crate) static EGL: Lazy<Option<Egl>> = Lazy::new(|| {
     #[cfg(windows)]
     let paths = ["libEGL.dll", "atioglxx.dll"];

diff --git a/glutin_examples/Cargo.toml b/glutin_examples/Cargo.toml
@@ -24,6 +24,7 @@ glutin-winit = { path = "../glutin-winit", default-features = false }
 png = { version = "0.17.6", optional = true }
 raw-window-handle = "0.6"
 winit = { version = "0.30.0", default-features = false, features = ["rwh_06"] }
+drm = { version = "0.12", optional = true }
 
 [target.'cfg(target_os = "android")'.dependencies]
 winit = { version = "0.30.0", default-features = false, features = ["android-native-activity", "rwh_06"] }
@@ -39,3 +40,7 @@ crate-type = ["cdylib"]
 [[example]]
 name = "egl_device"
 required-features = ["egl"]
+
+[[example]]
+name = "drm"
+required-features = ["egl", "drm"]
diff --git a/glutin_examples/examples/drm.rs b/glutin_examples/examples/drm.rs
@@ -0,0 +1,30 @@
+use std::fs::OpenOptions;
+use std::os::fd::AsRawFd;
+
+use glutin::api::egl;
+use raw_window_handle::{DrmDisplayHandle, RawDisplayHandle};
+
+fn main() {
+    let devices = egl::device::Device::query_devices().expect("Query EGL devices");
+    for egl_device in devices {
+        dbg!(&egl_device);
+        dbg!(egl_device.drm_render_device_node_path());
+        let Some(drm) = dbg!(egl_device.drm_device_node_path()) else {
+            continue;
+        };
+        let fd = OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open(drm)
+            .expect("Open DRM device with Read/Write permissions");
+
+        // https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_device_drm.txt:
+        // Providing DRM_MASTER_FD is only to cover cases where EGL might fail to open
+        // it itself.
+        let rdh = RawDisplayHandle::Drm(DrmDisplayHandle::new(fd.as_raw_fd()));
+
+        let egl_display = unsafe { egl::display::Display::with_device(&egl_device, Some(rdh)) }
+            .expect("Create EGL Display");
+        dbg!(&egl_display);
+    }
+}