libcamera: device_enumerator: add DeviceEnumeratorSysfs class

A udev-based device enumerator is not sufficient, since libudev is an
optional dependency, or udev might fail. In these cases, we should fall
back to using sysfs to enumerate devices.

Add a DeviceEnumeratorSysfs class which is a specialization of
DeviceEnumerator that uses sysfs to enumerate media devices on the
system.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Documentation/Doxyfile.in

@@ -833,7 +833,9 @@ RECURSIVE              = YES
 # Note that relative paths are relative to the directory from which doxygen is
 # run.
 
-EXCLUDE                = ../src/libcamera/device_enumerator_udev.cpp \
+EXCLUDE                = ../src/libcamera/device_enumerator_sysfs.cpp \
+			 ../src/libcamera/device_enumerator_udev.cpp \
+			 ../src/libcamera/include/device_enumerator_sysfs.h \
 			 ../src/libcamera/include/device_enumerator_udev.h \
 			 ../src/libcamera/pipeline/
 

src/libcamera/device_enumerator.cpp

@@ -6,6 +6,7 @@
  */
 
 #include "device_enumerator.h"
+#include "device_enumerator_sysfs.h"
 #include "device_enumerator_udev.h"
 
 #include <string.h>
@@ -153,8 +154,9 @@ std::unique_ptr<DeviceEnumerator> DeviceEnumerator::create()
 	 * Either udev is not available or udev initialization failed. Fall back
 	 * on the sysfs enumerator.
 	 */
-
-	/** \todo Add a sysfs-based enumerator. */
+	enumerator = utils::make_unique<DeviceEnumeratorSysfs>();
+	if (!enumerator->init())
+		return enumerator;
 
 	return nullptr;
 }

src/libcamera/device_enumerator_sysfs.cpp

@@ -0,0 +1,105 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * device_enumerator_sysfs.cpp - sysfs-based device enumerator
+ */
+
+#include "device_enumerator_sysfs.h"
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <fstream>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "log.h"
+
+namespace libcamera {
+
+LOG_DECLARE_CATEGORY(DeviceEnumerator)
+
+int DeviceEnumeratorSysfs::init()
+{
+	return 0;
+}
+
+int DeviceEnumeratorSysfs::enumerate()
+{
+	struct dirent *ent;
+	DIR *dir;
+
+	static const char * const sysfs_dirs[] = {
+		"/sys/subsystem/media/devices",
+		"/sys/bus/media/devices",
+		"/sys/class/media/devices",
+	};
+
+	for (const char *dirname : sysfs_dirs) {
+		dir = opendir(dirname);
+		if (dir)
+			break;
+	}
+
+	if (!dir) {
+		LOG(DeviceEnumerator, Error)
+			<< "No valid sysfs media device directory";
+		return -ENODEV;
+	}
+
+	while ((ent = readdir(dir)) != nullptr) {
+		if (strncmp(ent->d_name, "media", 5))
+			continue;
+
+		char *end;
+		unsigned int idx = strtoul(ent->d_name + 5, &end, 10);
+		if (*end != '\0')
+			continue;
+
+		std::string devnode = "/dev/media" + std::to_string(idx);
+
+		/* Verify that the device node exists. */
+		struct stat devstat;
+		if (stat(devnode.c_str(), &devstat) < 0) {
+			LOG(DeviceEnumerator, Warning)
+				<< "Device node /dev/media" << idx
+				<< " should exist but doesn't";
+			continue;
+		}
+
+		addDevice(devnode);
+	}
+
+	closedir(dir);
+
+	return 0;
+}
+
+std::string DeviceEnumeratorSysfs::lookupDeviceNode(int major, int minor)
+{
+	std::string deviceNode;
+	std::string line;
+	std::ifstream ueventFile;
+
+	ueventFile.open("/sys/dev/char/" + std::to_string(major) + ":" +
+			std::to_string(minor) + "/uevent");
+	if (!ueventFile)
+		return std::string();
+
+	while (ueventFile >> line) {
+		if (line.find("DEVNAME=") == 0) {
+			deviceNode = "/dev/" + line.substr(strlen("DEVNAME="));
+			break;
+		}
+	}
+
+	ueventFile.close();
+
+	return deviceNode;
+}
+
+} /* namespace libcamera */

src/libcamera/include/device_enumerator_sysfs.h

@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * device_enumerator_sysfs.h - sysfs-based device enumerator
+ */
+#ifndef __LIBCAMERA_DEVICE_ENUMERATOR_SYSFS_H__
+#define __LIBCAMERA_DEVICE_ENUMERATOR_SYSFS_H__
+
+#include <string>
+
+#include "device_enumerator.h"
+
+namespace libcamera {
+
+class DeviceEnumeratorSysfs final : public DeviceEnumerator
+{
+public:
+	int init();
+	int enumerate();
+
+private:
+	std::string lookupDeviceNode(int major, int minor);
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_DEVICE_ENUMERATOR_SYSFS_H__ */

src/libcamera/meson.build

@@ -4,6 +4,7 @@ libcamera_sources = files([
     'camera_manager.cpp',
     'camera_sensor.cpp',
     'device_enumerator.cpp',
+    'device_enumerator_sysfs.cpp',
     'event_dispatcher.cpp',
     'event_dispatcher_poll.cpp',
     'event_notifier.cpp',
@@ -26,6 +27,7 @@ libcamera_sources = files([
 libcamera_headers = files([
     'include/camera_sensor.h',
     'include/device_enumerator.h',
+    'include/device_enumerator_sysfs.h',
     'include/device_enumerator_udev.h',
     'include/event_dispatcher_poll.h',
     'include/formats.h',