event/InotifyEvent: new class wrapping inotify

Replaces class InotifySource.

src/event/InotifyEvent.cxx

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2022 CM4all GmbH
+ * All rights reserved.
+ *
+ * author: Max Kellermann <mk@cm4all.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "InotifyEvent.hxx"
+#include "system/Error.hxx"
+#include "io/UniqueFileDescriptor.hxx"
+
+#include <array>
+
+#include <limits.h>
+#include <sys/inotify.h>
+
+static UniqueFileDescriptor
+CreateInotify()
+{
+	int fd = inotify_init1(IN_CLOEXEC|IN_NONBLOCK);
+	if (fd < 0)
+		throw MakeErrno("inotify_init1() failed");
+
+	return UniqueFileDescriptor(fd);
+}
+
+InotifyEvent::InotifyEvent(EventLoop &event_loop, InotifyHandler &_handler)
+	:event(event_loop, BIND_THIS_METHOD(OnInotifyReady),
+	       CreateInotify().Release()),
+	 handler(_handler)
+{
+	Enable();
+}
+
+InotifyEvent::~InotifyEvent() noexcept
+{
+	Close();
+}
+
+int
+InotifyEvent::AddWatch(const char *pathname, uint32_t mask)
+{
+	int wd = inotify_add_watch(event.GetFileDescriptor().Get(),
+				   pathname, mask);
+	if (wd < 0)
+		throw FormatErrno("inotify_add_watch('%s') failed", pathname);
+
+	return wd;
+}
+
+int
+InotifyEvent::AddModifyWatch(const char *pathname)
+{
+	return AddWatch(pathname, IN_MODIFY);
+}
+
+void
+InotifyEvent::RemoveWatch(int wd) noexcept
+{
+	inotify_rm_watch(event.GetFileDescriptor().Get(), wd);
+}
+
+inline void
+InotifyEvent::OnInotifyReady(unsigned) noexcept
+try {
+	std::array<std::byte, 4096> buffer;
+	static_assert(sizeof(buffer) >= sizeof(struct inotify_event) + NAME_MAX + 1,
+		      "inotify buffer too small");
+
+	ssize_t nbytes = event.GetFileDescriptor().Read(buffer.data(),
+							buffer.size());
+	if (nbytes <= 0) [[unlikely]] {
+		if (nbytes == 0)
+			throw std::runtime_error{"EOF from inotify"};
+
+		const int e = errno;
+		if (e == EAGAIN)
+			return;
+
+		throw MakeErrno(e, "Reading inotify failed");
+	}
+
+	const std::byte *p = buffer.data(), *const end = p + nbytes;
+
+	while (true) {
+		const size_t remaining = end - p;
+		const auto &ie = *(const struct inotify_event *)(const void *)p;
+		if (remaining < sizeof(ie) ||
+		    remaining < sizeof(ie) + ie.len)
+			break;
+
+		const char *name;
+		if (ie.len > 0 && ie.name[ie.len - 1] == 0)
+			name = ie.name;
+		else
+			name = nullptr;
+
+		handler.OnInotify(ie.wd, ie.mask, name);
+		p += sizeof(ie) + ie.len;
+	}
+} catch (...) {
+	Close();
+	handler.OnInotifyError(std::current_exception());
+}

src/event/InotifyEvent.hxx

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2022 CM4all GmbH
+ * All rights reserved.
+ *
+ * author: Max Kellermann <mk@cm4all.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "PipeEvent.hxx"
+
+#include <exception>
+
+/**
+ * Handler for #InotifyEvent.
+ */
+class InotifyHandler {
+public:
+	/**
+	 * An inotify event was received.
+	 *
+	 * @param wd the watch descriptor returned by
+	 * InotifyEvent::AddWatch().
+	 */
+	virtual void OnInotify(int wd, unsigned mask, const char *name) = 0;
+
+	/**
+	 * An (permanent) inotify error has occurred, and the
+	 * #InotifyEvent has been closed.
+	 */
+	virtual void OnInotifyError(std::exception_ptr error) noexcept = 0;
+};
+
+/**
+ * #EventLoop integration for Linux inotify.
+ */
+class InotifyEvent final {
+	PipeEvent event;
+
+	InotifyHandler &handler;
+
+public:
+	/**
+	 * Create an inotify file descriptor add register it in the
+	 * #EventLoop.
+	 *
+	 * Throws on error.
+	 */
+	InotifyEvent(EventLoop &event_loop, InotifyHandler &_handler);
+
+	~InotifyEvent() noexcept;
+
+	EventLoop &GetEventLoop() const noexcept {
+		return event.GetEventLoop();
+	}
+
+	/**
+	 * Re-enable polling the inotify file descriptor after it was
+	 * disabled by Disable().
+	 */
+	void Enable() noexcept {
+		event.ScheduleRead();
+	}
+
+	/**
+	 * Disable polling the inotify file descriptor.  Can be
+	 * re-enabled by Enable().
+	 */
+	void Disable() noexcept {
+		event.Cancel();
+	}
+
+	/**
+	 * Permanently close the inotify file descriptor.  Further
+	 * method calls not allowed after that.
+	 */
+	void Close() noexcept {
+		event.Close();
+	}
+
+	/**
+	 * Register a new path to be watched.
+	 *
+	 * Throws on error.
+	 *
+	 * @return a watch descriptor
+	 */
+	int AddWatch(const char *pathname, uint32_t mask);
+
+	/**
+	 * Wrapper for AddWatch(pathname, IN_MODIFY).
+	 */
+	int AddModifyWatch(const char *pathname);
+
+	/**
+	 * Stop watching the given watch descriptor.
+	 *
+	 * @param wd a watch descriptor returned by AddWatch()
+	 */
+	void RemoveWatch(int wd) noexcept;
+
+private:
+	void OnInotifyReady(unsigned) noexcept;
+};

src/event/meson.build

@@ -19,6 +19,10 @@ else
   event_sources += 'PollBackend.cxx'
 endif
 
+if enable_inotify
+  event_sources += 'InotifyEvent.cxx'
+endif
+
 event = static_library(
   'event',
   'SignalMonitor.cxx',