read /etc/cachefilesd.conf

cachefilesd.conf

@@ -0,0 +1,8 @@
+dir /var/cache/fscache
+tag mycache
+brun 10%
+bcull 7%
+bstop 3%
+frun 10%
+fcull 7%
+fstop 3%

debian/changelog

@@ -1,5 +1,6 @@
 cm4all-cash (0.2) unstable; urgency=low
 
+  * read /etc/cachefilesd.conf
   * open /dev/cachefiles before opening the cache directory
   * systemd: add "RequiresMountsFor" and "CacheDirectory"
   * systemd: change "WantedBy" to "remote-fs.target"

meson.build

@@ -128,6 +128,7 @@ configure_file(output: 'config.h', configuration: conf)
 executable('cm4all-cash',
   'src/system/SetupProcess.cxx',
   'src/Main.cxx',
+  'src/Config.cxx',
   'src/Cull.cxx',
   'src/DevCachefiles.cxx',
   include_directories: inc,
@@ -142,3 +143,5 @@ executable('cm4all-cash',
   install: true,
   install_dir: 'sbin',
 )
+
+install_data('cachefilesd.conf', install_dir: get_option('sysconfdir'))

src/Config.cxx

@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// Copyright CM4all GmbH
+// author: Max Kellermann <[email protected]>
+
+#include "Config.hxx"
+#include "io/BufferedReader.hxx"
+#include "io/FdReader.hxx"
+#include "io/Open.hxx"
+#include "io/UniqueFileDescriptor.hxx"
+#include "util/CharUtil.hxx"
+#include "util/StringStrip.hxx"
+
+#include <charconv>
+#include <stdexcept>
+
+using std::string_view_literals::operator""sv;
+
+static constexpr bool
+IsCommandChar(char ch) noexcept
+{
+	return IsLowerAlphaASCII(ch);
+}
+
+static std::pair<std::string_view, std::string_view>
+ExtractCommandValue(const char *line)
+{
+	const char *p = line;
+
+	while (IsCommandChar(*p))
+		++p;
+
+	const std::string_view command{line, p};
+	if (command.empty())
+		throw std::runtime_error{"No command"};
+
+	if (IsWhitespaceNotNull(*p))
+		p = StripLeft(p + 1);
+	else if (*p != 0)
+		throw std::runtime_error{"Malformed command"};
+
+	return {command, StripRight(std::string_view{p})};
+}
+
+static uint_least8_t
+ParsePercent(std::string_view s)
+{
+	if (!s.ends_with('%'))
+		throw std::runtime_error{"Value must end with '%'"};
+
+	const char *const first = s.data(), *const last = first + s.size() - 1;
+
+	uint_least8_t value;
+	auto [ptr, ec] = std::from_chars(first, last, value, 10);
+	if (ptr == first || ptr != last || ec != std::errc{})
+		throw std::runtime_error{"Malformed number"};
+
+	return value;
+}
+
+Config
+LoadConfigFile(const char *path)
+{
+	Config config;
+	auto kernel_config_iterator = config.kernel_config.before_begin();
+
+	const auto fd = OpenReadOnly(path);
+	FdReader fd_reader{fd};
+	BufferedReader r{fd_reader};
+
+	while (const char *line = r.ReadLine()) {
+		line = StripLeft(line);
+		if (*line == 0 || *line == '#')
+			continue;
+
+		const auto [command, value] = ExtractCommandValue(line);
+		if (command == "dir"sv)
+			config.dir = value;
+		else if (command == "brun"sv)
+			config.brun = ParsePercent(value);
+		else if (command == "frun"sv)
+			config.frun = ParsePercent(value);
+
+		kernel_config_iterator =
+			config.kernel_config.emplace_after(kernel_config_iterator,
+							   command.begin(), value.end());
+	}
+
+	if (config.dir.empty())
+		throw std::runtime_error{"No 'dir' setting"};
+
+	return config;
+}

src/Config.hxx

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// Copyright CM4all GmbH
+// author: Max Kellermann <[email protected]>
+
+#pragma once
+
+#include <cstdint>
+#include <forward_list>
+#include <string>
+
+struct Config {
+	std::string dir;
+
+	std::forward_list<std::string> kernel_config;
+
+	uint_least8_t brun = 10, frun = 10;
+};
+
+Config
+LoadConfigFile(const char *path);

src/Instance.hxx

@@ -16,6 +16,10 @@
 #include "event/systemd/Watchdog.hxx"
 #endif
 
+#include <cstdint>
+
+struct Config;
+
 class Instance {
 	EventLoop event_loop;
 	ShutdownListener shutdown_listener{event_loop, BIND_THIS_METHOD(OnShutdown)};
@@ -32,8 +36,10 @@ class Instance {
 
 	std::optional<Cull> cull;
 
+	const uint_least8_t brun, frun;
+
 public:
-	Instance();
+	explicit Instance(const Config &config);
 	~Instance() noexcept;
 
 	void Run();

src/Main.cxx

@@ -3,6 +3,7 @@
 // author: Max Kellermann <[email protected]>
 
 #include "Instance.hxx"
+#include "Config.hxx"
 #include "system/Error.hxx"
 #include "system/SetupProcess.hxx"
 #include "io/Open.hxx"
@@ -34,43 +35,29 @@
 
 using std::string_view_literals::operator""sv;
 
-// TODO hard-coded configuration
-static constexpr unsigned brun = 10, frun = 10;
-
 static UniqueFileDescriptor
-OpenDevCachefiles()
+OpenDevCachefiles(const Config &config)
 {
 	UniqueFileDescriptor fd;
 	if (!fd.Open("/dev/cachefiles", O_RDWR))
 		throw MakeErrno("Failed to open /dev/cachefiles");
 
-	// TODO hard-coded configuration
-	static constexpr const char *configure_cachefiles[] = {
-		"dir /var/cache/fscache",
-		"tag mycache",
-		"brun 10%",
-		"brun 10%",
-		"bcull 7%",
-		"bstop 3%",
-		"frun 10%",
-		"fcull 7%",
-		"fstop 3%",
-		"bind",
-	};
+	for (const auto &line : config.kernel_config)
+		fd.FullWrite(AsBytes(line));
 
-	for (const char *s : configure_cachefiles)
-		fd.FullWrite(AsBytes(std::string_view{s}));
+	fd.FullWrite(AsBytes("bind"sv));
 
 	return fd;
 }
 
 inline
-Instance::Instance()
+Instance::Instance(const Config &config)
+	:brun(config.brun), frun(config.frun)
 {
-	dev_cachefiles.Open(OpenDevCachefiles().Release());
+	dev_cachefiles.Open(OpenDevCachefiles(config).Release());
 	dev_cachefiles.ScheduleRead();
 
-	const auto fscache_fd = OpenPath("/var/cache/fscache", O_DIRECTORY);
+	const auto fscache_fd = OpenPath(config.dir.c_str(), O_DIRECTORY);
 	cache_fd = OpenPath(fscache_fd, "cache", O_DIRECTORY);
 	graveyard_fd = OpenPath(fscache_fd, "graveyard", O_DIRECTORY);
 
@@ -152,7 +139,9 @@ Instance::Run()
 static int
 Run()
 {
-	Instance instance;
+	Instance instance{
+		LoadConfigFile("/etc/cachefilesd.conf"),
+	};
 
 #ifdef HAVE_LIBCAP
 	/* drop all capabilities, we don't need them anymore */