[PATCH v2] libcamera: udev: Catch udev notification errors

[Kieran Bingham]

Quoting Laurent Pinchart (2024-08-07 15:24:55)
> Hi Kieran,
> 
> Thank you for the patch.
> 
> On Wed, Aug 07, 2024 at 02:49:50PM +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
> > Reviewed-by: Stefan Klug <stefan.klug at ideasonboard.com>
> > Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > 
> > ---
> > v2:
> >  - Report strerror based on errno from the udev_monitor_receive_device()
> >    call.
> > 
> >  src/libcamera/device_enumerator_udev.cpp | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/src/libcamera/device_enumerator_udev.cpp b/src/libcamera/device_enumerator_udev.cpp
> > index 01c70b6daa82..53eeb772d900 100644
> > --- a/src/libcamera/device_enumerator_udev.cpp
> > +++ b/src/libcamera/device_enumerator_udev.cpp
> > @@ -332,6 +332,14 @@ int DeviceEnumeratorUdev::addV4L2Device(dev_t devnum)
> >  void DeviceEnumeratorUdev::udevNotify()
> >  {
> >       struct udev_device *dev = udev_monitor_receive_device(monitor_);
> > +     if (!dev) {
> > +             int error = errno;
> 
> grepping for ' = errno' gives me 12 variables named ret, and one named
> err. I'd go for 'ret' here too for consitency.

I explicitly didn't use 'ret' because it's not a ret value...

And 'err' was just shorthand. I'll rename if you wish, but please
confirm.

> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
> Could you ask the bug reporter to test this patch and tell what error
> number they get ?

Yes, but I don't know how they'll test it, as it's part of a separate CI
system, so I don't think we'll get a response (until it filters into a
release, that then gets utilised in that CI system).

--
Kieran



> 
> > +             LOG(DeviceEnumerator, Warning)
> > +                     << "Ignoring notfication received without a device: "
> > +                     << strerror(error);
> > +             return;
> > +     }
> > +
> >       std::string_view action(udev_device_get_action(dev));
> >       std::string_view deviceNode(udev_device_get_devnode(dev));
> >  
> 
> -- 
> Regards,
> 
> Laurent Pinchart