[libcamera-devel] [PATCH v2 5/5] tests: Introduce hotplug hot-unplug unit test

[Umang Jain]

Hi Kieran,

On Mon, 2020-05-18 at 16:57 +0100, Kieran Bingham wrote:
> Hi Umang,
> 
> I'm happy to see a hotplug test here, and I know this one is quite a
> pain to write ;-)
> 
> On 13/05/2020 18:30, Umang Jain wrote:
> 
> A bit of blurb about what happens in the test is always useful in the
> commit message here.
> 
> It's also particularly worth mentioning that the test will skip if
> not
> run as root due to the requirement to modify the bind state of the
> device, and of course that it requires a UVC device to be connected
> for
> test.
> 
> 
> > Signed-off-by: Umang Jain <email at uajain.com>
> > ---
> >  test/hotplug-cameras.cpp | 152
> > +++++++++++++++++++++++++++++++++++++++
> >  test/meson.build         |   1 +
> >  2 files changed, 153 insertions(+)
> >  create mode 100644 test/hotplug-cameras.cpp
> > 
> > diff --git a/test/hotplug-cameras.cpp b/test/hotplug-cameras.cpp
> > new file mode 100644
> > index 0000000..cbf68af
> > --- /dev/null
> > +++ b/test/hotplug-cameras.cpp
> > @@ -0,0 +1,152 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> > +/*
> > + * Copyright (C) 2020, Umang Jain <email at uajain.com>
> > + *
> > + * hotplug-cameras.cpp - Emulate cameraAdded/cameraRemoved signals
> > in CameraManager
> > + */
> > +
> > +#include <dirent.h>
> > +#include <fstream>
> > +#include <iostream>
> > +#include <string.h>
> > +#include <unistd.h>
> > +
> > +#include <fcntl.h>
> > +#include <sys/stat.h>
> > +#include <sys/types.h>
> > +
> > +#include <libcamera/camera.h>
> > +#include <libcamera/camera_manager.h>
> > +#include <libcamera/event_dispatcher.h>
> > +#include <libcamera/timer.h>
> > +
> > +#include "file.h"
> > +#include "test.h"
> > +#include "thread.h"
> > +
> > +using namespace std;
> > +using namespace libcamera;
> > +
> > +class HotplugTest : public Test
> > +{
> > +protected:
> > +	void cameraAddedHandler(std::shared_ptr<Camera> cam)
> > +	{
> > +		cameraAddedPass_ = true;
> > +	}
> > +
> > +	void cameraRemovedHandler(std::shared_ptr<Camera> cam)
> > +	{
> > +		cameraRemovedPass_ = true;
> > +	}
> > +
> > +	int init()
> > +	{
> > +		if (!File::exists("/sys/module/uvcvideo")) {
> > +			std::cout << "uvcvideo driver is not loaded,
> > skipping" << std::endl;
> > +			return TestSkip;
> > +		}
> > +
> > +		if (geteuid() != 0) {
> > +			std::cout << "This test requires root
> > permissions, skipping" << std::endl;
> > +			return TestSkip;
> > +		}
> > +
> > +		cm_ = new CameraManager();
> > +		if (cm_->start()) {
> > +			std::cout << "Failed to start camera manager"
> > << std::endl;
> > +			return TestFail;
> > +		}
> > +
> > +		cameraAddedPass_ = false;
> > +		cameraRemovedPass_ = false;
> > +
> > +		cm_->cameraAdded.connect(this,
> > &HotplugTest::cameraAddedHandler);
> > +		cm_->cameraRemoved.connect(this,
> > &HotplugTest::cameraRemovedHandler);
> > +
> > +		uvc_toplevel_ =
> > "/sys/module/uvcvideo/drivers/usb:uvcvideo/";
> > +
> > +		return 0;
> > +	}
> > +
> > +	int run()
> > +	{
> > +		DIR *dir;
> > +		struct dirent *dirent, *dirent2;
> > +		std::string uvc_driver_dir;
> > +		bool uvc_driver_found = false;
> > +
> > +		dir = opendir(uvc_toplevel_.c_str());
> > +		/* Find a UVC device driver symlink, which we can
> > bind/unbind */
> > +		while ((dirent = readdir(dir)) != nullptr) {
> > +			if (dirent->d_type != DT_LNK)
> > +				continue;
> > +
> > +			std::string child_dir = uvc_toplevel_ + dirent-
> > >d_name;
> > +			DIR *device_driver =
> > opendir(child_dir.c_str());
> > +			while ((dirent2 = readdir(device_driver)) !=
> > nullptr) {
> > +				if (strncmp(dirent2->d_name,
> > "video4linux", 11) == 0) {
> > +					uvc_driver_dir = dirent-
> > >d_name;
> > +					uvc_driver_found = true;
> > +					break;
> > +				}
> > +			}
> > +			closedir(device_driver);
> > +
> > +			if (uvc_driver_found)
> > +				break;
> > +		}
> > +		closedir(dir);
> > +
> > +		/* If no UVC driver found, skip */
> > +		if (!uvc_driver_found)
> > +			return TestSkip;
> > +
> > +		/* Unbind a camera, process events */
> > +		int fd1 =
> > open("/sys/module/uvcvideo/drivers/usb:uvcvideo/unbind", O_WRONLY);
> > +		write(fd1, uvc_driver_dir.c_str(),
> > uvc_driver_dir.size());
> > +		close(fd1);
> > +		Timer timer;
> > +		timer.start(1000);
> > +		while (timer.isRunning())
> > +			Thread::current()->eventDispatcher()-
> > >processEvents();
> > +
> > +		/* \todo: Fix this workaround of stopping and starting
> > the camera-manager.
> > +		 *  We need to do this, so that cm_ release all
> > references to the uvc media symlinks.
> 
> Eep, I can't get my head around this just yet. You mean having the
> camera manager running, it has open handles to the media symlinks in
> sysfs perhaps?
> 
> I guess it's implying that something in the cm_ is preventing the
> clean
> unbind of the camera - but I don't understand what that is yet to
> know
> if we must fix that, or if it's something unavoidable?

Yes, let me explain with an observation from the 'master' branch of
libcamera(i.e. without these patches).

I have a UVC camera and is denoted by "1-1:1.0" and "1-1:1.1" symlinks
in '/sys/module/uvcvideo/drivers/usb:uvcvideo'. Now, with qcam
streaming from this device, try to unbind and re-bind the "1-1:1.0"
symlink (which  is the primary video device node). Obviously, qcam
won't pick up the re-binding again but notice what happens when you
exit the qcam and try to re-run qcam again; qcam won't notice the
device when it's restarted.

Yet another observation while following the above mentioned process,
when I have qcam running and I unbind "1-1:1.0", the symlink "1-1:1.1"
doesn't get dis-appeared(apparently it should). It only gets disappered
(i.e. device has been cleanly unbind) only when qcam is closed at this
point; which explains CameraManager is holding some kind of ref on this
symlink.
> 
> But we're not going to expect applications to stop and restart the
> camera manager, so I certainly hope this is just because of the fact
> we're using the unbind/bind mechanism?

Yes, that's my observation as well. This problem(and hence the
workaround in the test) is specific to bind/unbind mechanism. I tested
with a handy USB webcam around, and it doesn't leave any dangling
symlinks.

> If not - then we really need to fix it ;-)
> 
I am still looking into it, it might be a silly leak somewhere but
getting hard to find :)

> > +		 */
> > +		cm_->stop();
> > +		if (cm_->start()) {
> > +			std::cout << "Failed to restart camera-manager" 
> > << std::endl;
> > +			return TestFail;
> > +		}
> > +
> > +		/* Bind the camera again, process events */
> > +		int fd2 =
> > open("/sys/module/uvcvideo/drivers/usb:uvcvideo/bind", O_WRONLY);
> > +		write(fd2, uvc_driver_dir.c_str(),
> > uvc_driver_dir.size());
> > +		close(fd2);
> > +
> > +		timer.start(1000);
> > +		while (timer.isRunning())
> > +			Thread::current()->eventDispatcher()-
> > >processEvents();
> > +
> > +		if (cameraAddedPass_ && cameraRemovedPass_)
> > +			return TestPass;
> > +		else
> > +			return TestFail;
> > +	}
> > +
> > +	void cleanup()
> > +	{
> > +		cm_->stop();
> > +		delete cm_;
> > +	}
> > +
> > +private:
> > +	CameraManager *cm_;
> > +	std::string uvc_toplevel_;
> > +	bool cameraRemovedPass_;
> > +	bool cameraAddedPass_;
> > +};
> > +
> > +TEST_REGISTER(HotplugTest)
> > +
> > diff --git a/test/meson.build b/test/meson.build
> > index 5a45a85..383a7ea 100644
> > --- a/test/meson.build
> > +++ b/test/meson.build
> > @@ -29,6 +29,7 @@ internal_tests = [
> >      ['file',                            'file.cpp'],
> >      ['file-descriptor',                 'file-descriptor.cpp'],
> >      ['message',                         'message.cpp'],
> > +    ['hotplug-cameras',                 'hotplug-cameras.cpp'],
> >      ['object',                          'object.cpp'],
> >      ['object-invoke',                   'object-invoke.cpp'],
> >      ['signal-threads',                  'signal-threads.cpp'],
> >