syncobj::fd_to_handle with import_sync_file = true is wrong

[YaLTeR]

DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE imports a fence fd into an existing syncobj handle which needs to be passed into handle. But the current function always passes handle: 0 on line 73 so it cannot work:

drm-rs/drm-ffi/src/syncobj.rs

Lines 67 to 88 in b65efbc

	pub fn fd_to_handle(
	fd: BorrowedFd<'_>,
	syncobj_fd: BorrowedFd<'_>,
	import_sync_file: bool,
	) -> io::Result<drm_syncobj_handle> {
	let mut args = drm_syncobj_handle {
	handle: 0,
	flags: if import_sync_file {
	DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE
	} else {
	0
	},
	fd: syncobj_fd.as_raw_fd(),
	pad: 0,
	};
	unsafe {
	ioctl::syncobj::fd_to_handle(fd, &mut args)?;
	}
	Ok(args)
	}

The API should have a separate function like:

pub fn syncobj_import_sync_file(
    fd: BorrowedFd<'_>,
    handle: u32,
    sync_file: BorrowedFd<'_>,
) -> io::Result<drm_syncobj_handle> {
    let mut args = drm_syncobj_handle {
        handle,
        flags: DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE,
        fd: sync_file.as_raw_fd(),
        pad: 0,
    };

    unsafe {
        ioctl::syncobj::fd_to_handle(fd, &mut args)?;
    }

    Ok(args)
}

(idk if the return value is any useful here)

[MarijnS95]

That seems about right for sync_file. This confusion likely exists because the opposite is true for the non-sync_file variant, where a new handle is created, per the docs:

https://github.com/torvalds/linux/blob/2942242dde896ea8544f321617c86f941899c544/drivers/gpu/drm/drm_syncobj.c#L159-L165

And the implementation assigning/overwriting the handle:

https://github.com/torvalds/linux/blob/2942242dde896ea8544f321617c86f941899c544/drivers/gpu/drm/drm_syncobj.c#L735

For sync_files it clearly says it's being imported into a syncobj:

https://github.com/torvalds/linux/blob/2942242dde896ea8544f321617c86f941899c544/drivers/gpu/drm/drm_syncobj.c#L176-L177

And the implementation that searches for the syncobj based on the handle:

https://github.com/torvalds/linux/blob/2942242dde896ea8544f321617c86f941899c544/drivers/gpu/drm/drm_syncobj.c#L752-L756

[MarijnS95]

Most likely these APIs need a bit of a refactor to not return the full struct but an OwnedFd. Right now they already take BorrowedFds but that re-wrapping is handled one level outside of drm-ffi, directly in drm 🤯