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>

1 files changed, 105 insertions, 0 deletions

diff --git a/src/libcamera/device_enumerator_sysfs.cpp b/src/libcamera/device_enumerator_sysfs.cpp
new file mode 100644
index 00000000..f3054d5e
--- /dev/null
+++ b/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 */