[PATCH] libcamera: udev: Catch udev notification errors

[Kieran Bingham]

The udev_monitor_receive_device() can return NULL on an error as
detailed in the man pages for the function.

The udevNotify() handler in the DeviceEnumeratorUdev directly uses the
return value of udev_monitor_receive_device() in successive calls to
process the event without having first checked the udev_device.

Ensure we identify, and handle events where the udev_device can not be
returned successfully.

Bug: https://bugs.libcamera.org/show_bug.cgi?id=230
Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---
This is a proposed fix for the reported CI failure caught by Systemd
runners. It's not clear if this failure was an injected failure, startup
race or otherwise - but given the documentation of this function states
it can return null ... it seems valid to null check before passing into
other APIs especially when a trace is reported directly at this point.

I don't presently have a way to replicate or reproduce the error either,
but this patch itself has passed our ci tests (which isn't too
unexpected as the change is quite minimal otherwise).


 src/libcamera/device_enumerator_udev.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/libcamera/device_enumerator_udev.cpp b/src/libcamera/device_enumerator_udev.cpp
index 01c70b6daa82..c6c78651baa0 100644
--- a/src/libcamera/device_enumerator_udev.cpp
+++ b/src/libcamera/device_enumerator_udev.cpp
@@ -332,6 +332,12 @@ int DeviceEnumeratorUdev::addV4L2Device(dev_t devnum)
 void DeviceEnumeratorUdev::udevNotify()
 {
 	struct udev_device *dev = udev_monitor_receive_device(monitor_);
+	if (!dev) {
+		LOG(DeviceEnumerator, Warning)
+			<< "Ignoring notfication received without a device";
+		return;
+	}
+
 	std::string_view action(udev_device_get_action(dev));
 	std::string_view deviceNode(udev_device_get_devnode(dev));
 
-- 
2.45.2