[libcamera-devel] [PATCH] libcamera: device_enumerator: add DeviceEnumeratorSysfs class

[Paul Elder]

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 at ideasonboard.com>
---
 Documentation/Doxyfile.in                     |   2 +
 src/libcamera/device_enumerator.cpp           |   6 +-
 src/libcamera/device_enumerator_sysfs.cpp     | 109 ++++++++++++++++++
 .../include/device_enumerator_sysfs.h         |  31 +++++
 src/libcamera/meson.build                     |   2 +
 5 files changed, 148 insertions(+), 2 deletions(-)
 create mode 100644 src/libcamera/device_enumerator_sysfs.cpp
 create mode 100644 src/libcamera/include/device_enumerator_sysfs.h

diff --git a/Documentation/Doxyfile.in b/Documentation/Doxyfile.in
index 950ad4f..5dd4445 100644
--- a/Documentation/Doxyfile.in
+++ b/Documentation/Doxyfile.in
@@ -835,6 +835,8 @@ RECURSIVE              = YES
 
 EXCLUDE                = ../src/libcamera/device_enumerator_udev.cpp \
 			 ../src/libcamera/include/device_enumerator_udev.h \
+			 ../src/libcamera/device_enumerator_sysfs.cpp \
+			 ../src/libcamera/include/device_enumerator_sysfs.h \
 			 ../src/libcamera/pipeline/
 
 # The EXCLUDE_SYMLINKS tag can be used to select whether or not files or
diff --git a/src/libcamera/device_enumerator.cpp b/src/libcamera/device_enumerator.cpp
index f6878b3..5c44eb1 100644
--- a/src/libcamera/device_enumerator.cpp
+++ b/src/libcamera/device_enumerator.cpp
@@ -7,6 +7,7 @@
 
 #include "device_enumerator.h"
 #include "device_enumerator_udev.h"
+#include "device_enumerator_sysfs.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;
 }
diff --git a/src/libcamera/device_enumerator_sysfs.cpp b/src/libcamera/device_enumerator_sysfs.cpp
new file mode 100644
index 0000000..6dd04e8
--- /dev/null
+++ b/src/libcamera/device_enumerator_sysfs.cpp
@@ -0,0 +1,109 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2018-2019, Google Inc.
+ *
+ * device_enumerator_sysfs.cpp - udev-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)
+
+DeviceEnumeratorSysfs::DeviceEnumeratorSysfs()
+{
+}
+
+DeviceEnumeratorSysfs::~DeviceEnumeratorSysfs()
+{
+}
+
+int DeviceEnumeratorSysfs::init()
+{
+	return 0;
+}
+
+int DeviceEnumeratorSysfs::enumerate()
+{
+	struct dirent *ent;
+	struct stat devstat;
+	char *end;
+	DIR *dir;
+
+	static const char *sysfs_dirs[] = {
+		"/sys/media/devices",
+		"/sys/block/media/devices",
+		"/sys/bus/media/devices",
+		"/sys/class/media/devices",
+	};
+
+	for (const char *dirname : sysfs_dirs) {
+		dir = opendir(dirname);
+		if (dir)
+			break;
+	}
+
+	while ((ent = readdir(dir)) != nullptr) {
+		unsigned int idx;
+		std::string devnode = std::string();
+
+		if (strncmp(ent->d_name, "media", 5))
+			continue;
+
+		idx = strtoul(ent->d_name + 5, &end, 10);
+		if (*end != '\0')
+			continue;
+
+		devnode = "/dev/media" + std::to_string(idx);
+
+		/* Verify that the device node exists. */
+		if (stat(devnode.c_str(), &devstat) < 0)
+			continue;
+
+		addDevice(devnode);
+	}
+
+	closedir(dir);
+
+	return 0;
+}
+
+std::string DeviceEnumeratorSysfs::lookupDeviceNode(int major, int minor)
+{
+	std::string deviceNode = std::string();
+	std::string line = std::string();
+	std::ifstream uevent_file;
+	size_t c_cnt;
+
+	uevent_file.open("/sys/dev/char/" + std::to_string(major) + ":" +
+			 std::to_string(minor) + "/uevent");
+	if (!uevent_file)
+		return std::string();
+
+	while (uevent_file >> line) {
+		if (line.find("DEVNAME") != std::string::npos) {
+			c_cnt = line.find("=");
+			deviceNode = "/dev/" + line.substr(c_cnt + 1);
+			break;
+		}
+	}
+
+	uevent_file.close();
+
+	return deviceNode;
+}
+
+} /* namespace libcamera */
diff --git a/src/libcamera/include/device_enumerator_sysfs.h b/src/libcamera/include/device_enumerator_sysfs.h
new file mode 100644
index 0000000..f32d6ae
--- /dev/null
+++ b/src/libcamera/include/device_enumerator_sysfs.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2018-2019, 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 : public DeviceEnumerator
+{
+public:
+	DeviceEnumeratorSysfs();
+	~DeviceEnumeratorSysfs();
+
+	int init() final;
+	int enumerate() final;
+
+private:
+	std::string lookupDeviceNode(int major, int minor) final;
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_DEVICE_ENUMERATOR_SYSFS_H__ */
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index 2b67823..ca9ed7a 100644
--- a/src/libcamera/meson.build
+++ b/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',
@@ -27,6 +28,7 @@ libcamera_headers = files([
     'include/camera_sensor.h',
     'include/device_enumerator.h',
     'include/device_enumerator_udev.h',
+    'include/device_enumerator_sysfs.h',
     'include/event_dispatcher_poll.h',
     'include/formats.h',
     'include/log.h',
-- 
2.20.1