[PATCH xf86-input-libinput] Replace the "fd" option when enabling dependent devices

[Peter Hutterer]

The server uses pInfo->major/minor to detect if another device is using the
same path for a logind-controlled fd. If so, it reuses that device's
pInfo->fd and sets the "fd" option to that value.

That pInfo->fd is the libinput epollfd though, not the actual device fd.

This doesn't matter for us, since we manage the fds largely ourselves and the
pInfo->fd we use is the epollfd anyway. On unplug however, the udev code
triggers a device removal for all devices, including the duplicated ones. When
we disable device, we restore the pInfo->fd from the "fd" option so that the
server can request logind to close the fd.

That only works if the "fd" option is correct, otherwise the server asks
logind to close the epollfd and everyone is unhappy.

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
I had to revert the patch shortly after pushing because it caused hangs in a
logind setup on device unplug. This is on top of the original bug since it's
a bit convoluted and a lot easier to understand when it's not squashed in.
For the actual final patch, I'll squash them together though.

Not happy with this approach, but short of a big rewrite of the server's
input APIs there isn't that much we can do. And no-one is keen to do that
atm :)

 src/xf86libinput.c | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/src/xf86libinput.c b/src/xf86libinput.c
index 430fc9a..ee2165a 100644
--- a/src/xf86libinput.c
+++ b/src/xf86libinput.c
@@ -83,6 +83,7 @@ struct xf86libinput_device {
 	uint32_t id;
 	struct libinput_device *device;
 	struct xorg_list device_list;
+	int server_fd;
 };
 
 struct xf86libinput {
@@ -236,15 +237,40 @@ xf86libinput_shared_unref(struct xf86libinput_device *shared_device)
 }
 
 static inline struct libinput_device *
-xf86libinput_shared_enable(struct xf86libinput_device *shared_device,
+xf86libinput_shared_enable(InputInfoPtr pInfo,
+			   struct xf86libinput_device *shared_device,
 			   const char *path)
 {
 	struct libinput_device *device;
 	struct libinput *libinput = driver_context.libinput;
 
+	/* With systemd-logind the server requests the fd from logind, sets
+	 * pInfo->fd and sets the "fd" option to the fd number.
+	 *
+	 * If we have a second device that uses the same path, the server
+	 * checks all pInfo->major/minor for a match and returns the matched
+	 * device's pInfo->fd. In this driver, this fd is the epollfd, not
+	 * the actual device. This causes troubles when removing the
+	 * device.
+	 *
+	 * What we need to do here is: after enabling the device the first
+	 * time extract the real fd and store it in the shared device
+	 * struct. The second device replaces the pInfo->options "fd" with
+	 * the real fd we're using.
+	 *
+	 * When the device is unplugged, the server now correctly finds two
+	 * devices on the real fd and releases them in order.
+	 */
 	shared_device->enabled_count++;
-	if (shared_device->enabled_count > 1)
+	if (shared_device->enabled_count > 1) {
+		if (pInfo->flags & XI86_SERVER_FD) {
+			pInfo->options = xf86ReplaceIntOption(pInfo->options,
+							      "fd",
+							      shared_device->server_fd);
+		}
+
 		return shared_device->device;
+	}
 
 	device = libinput_path_add_device(libinput, path);
 	if (!device)
@@ -253,6 +279,10 @@ xf86libinput_shared_enable(struct xf86libinput_device *shared_device,
 	libinput_device_set_user_data(device, shared_device);
 	shared_device->device = libinput_device_ref(device);
 
+	if (pInfo->flags & XI86_SERVER_FD)
+		shared_device->server_fd = xf86CheckIntOption(pInfo->options,
+							      "fd",
+							      -1);
 	return device;
 }
 
@@ -437,7 +467,8 @@ xf86libinput_on(DeviceIntPtr dev)
 	struct libinput *libinput = driver_context.libinput;
 	struct libinput_device *device;
 
-	device = xf86libinput_shared_enable(shared_device,
+	device = xf86libinput_shared_enable(pInfo,
+					    shared_device,
 					    driver_data->path);
 	if (!device)
 		return !Success;
-- 
2.5.0