gbm: detect gbm_bo_get_fd_for_plane

When available or forced with feature
backend_gbm_has_fd_for_plane use fd_for_plane
which allows the use of multi planar formats
which expose multiple planes with different fds.

Cargo.toml

@@ -69,13 +69,15 @@ slog-term = "2.3"
 [build-dependencies]
 gl_generator = { version = "0.14", optional = true }
 pkg-config = { version = "0.3.17", optional = true }
+cc = { version = "1.0", optional = true }
 
 [features]
 default = ["backend_drm", "backend_gbm", "backend_libinput", "backend_udev", "backend_session_logind", "backend_x11", "backend_winit", "desktop", "renderer_gl", "renderer_multi", "xwayland", "wayland_frontend", "slog-stdlog", "backend_vulkan"]
 backend_winit = ["winit", "backend_egl", "wayland-egl", "renderer_gl"]
 backend_x11 = ["x11rb", "x11rb/dri3", "x11rb/xfixes", "x11rb/present", "x11rb_event_source", "backend_gbm", "backend_drm", "backend_egl"]
 backend_drm = ["drm", "drm-ffi"]
-backend_gbm = ["gbm"]
+backend_gbm = ["gbm", "cc", "pkg-config"]
+backend_gbm_has_fd_for_plane = []
 backend_egl = ["gl_generator", "libloading"]
 backend_libinput = ["input"]
 backend_session = []

build.rs

@@ -97,10 +97,35 @@ fn find_logind() {
     }
 }
 
+#[cfg(all(feature = "backend_gbm", not(feature = "backend_gbm_has_fd_for_plane")))]
+fn test_gbm_bo_fd_for_plane() {
+    let gbm = match pkg_config::probe_library("gbm") {
+        Ok(lib) => lib,
+        Err(_) => {
+            println!("cargo:warning=failed to find gbm, assuming gbm_bo_get_fd_for_plane is unavailable");
+            return;
+        }
+    };
+
+    let has_gbm_bo_get_fd_for_plane = cc::Build::new()
+        .file("test_gbm_bo_get_fd_for_plane.c")
+        .includes(gbm.include_paths)
+        .warnings_into_errors(true)
+        .try_compile("test_gbm_bo_get_fd_for_plane")
+        .is_ok();
+
+    if has_gbm_bo_get_fd_for_plane {
+        println!("cargo:rustc-cfg=feature=\"backend_gbm_has_fd_for_plane\"");
+    }
+}
+
 fn main() {
     #[cfg(any(feature = "backend_egl", feature = "renderer_gl"))]
     gl_generate();
 
     #[cfg(feature = "backend_session_logind")]
     find_logind();
+
+    #[cfg(all(feature = "backend_gbm", not(feature = "backend_gbm_has_fd_for_plane")))]
+    test_gbm_bo_fd_for_plane();
 }

src/backend/allocator/gbm.rs

@@ -74,10 +74,36 @@ pub enum GbmConvertError {
 impl<T> AsDmabuf for GbmBuffer<T> {
     type Error = GbmConvertError;
 
+    #[cfg(feature = "backend_gbm_has_fd_for_plane")]
+    fn export(&self) -> Result<Dmabuf, GbmConvertError> {
+        let planes = self.plane_count()? as i32;
+
+        let mut builder = Dmabuf::builder_from_buffer(self, DmabufFlags::empty());
+        for idx in 0..planes {
+            let fd = self.fd_for_plane(idx)?;
+
+            // gbm_bo_get_fd_for_plane returns -1 if an error occurs
+            if fd == -1 {
+                return Err(GbmConvertError::InvalidFD);
+            }
+
+            builder.add_plane(
+                // SAFETY: `gbm_bo_get_fd_for_plane` returns a new fd owned by the caller.
+                unsafe { OwnedFd::from_raw_fd(fd) },
+                idx as u32,
+                self.offset(idx)?,
+                self.stride_for_plane(idx)?,
+                self.modifier()?,
+            );
+        }
+
+        Ok(builder.build().unwrap())
+    }
+
+    #[cfg(not(feature = "backend_gbm_has_fd_for_plane"))]
     fn export(&self) -> Result<Dmabuf, GbmConvertError> {
         let planes = self.plane_count()? as i32;
 
-        //TODO switch to gbm_bo_get_plane_fd when it lands
         let mut iter = (0i32..planes).map(|i| self.handle_for_plane(i));
         let first = iter.next().expect("Encountered a buffer with zero planes");
         // check that all handles are the same

test_gbm_bo_get_fd_for_plane.c

@@ -0,0 +1,5 @@
+#include <gbm.h>
+
+void test() {
+    gbm_bo_get_fd_for_plane(NULL, 0);
+}