[PATCH] libcamera: udev: Catch udev notification errors

[Stefan Klug]

Hi Kieran,

Thank you for the patch. 

On Mon, Aug 05, 2024 at 11:31:48PM +0100, Kieran Bingham wrote:
> 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";

Is that even worth a warning or only debug?

Anyways:
Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com> 

Cheers,
Stefan

> +		return;
> +	}
> +
>  	std::string_view action(udev_device_get_action(dev));
>  	std::string_view deviceNode(udev_device_get_devnode(dev));
>  
> -- 
> 2.45.2
>