Kernel: Implement linux's eventfd

kernel/kernel/FS/EventFD.cpp

@@ -0,0 +1,54 @@
+#include <kernel/FS/EventFD.h>
+
+#include <sys/epoll.h>
+
+namespace Kernel
+{
+
+	BAN::ErrorOr<BAN::RefPtr<Inode>> EventFD::create(uint64_t initval, bool semaphore)
+	{
+		auto* eventfd_ptr = new EventFD(initval, semaphore);
+		if (eventfd_ptr == nullptr)
+			return BAN::Error::from_errno(ENOMEM);
+		return BAN::RefPtr<Inode>(BAN::RefPtr<EventFD>::adopt(eventfd_ptr));
+	}
+
+	BAN::ErrorOr<size_t> EventFD::read_impl(off_t, BAN::ByteSpan buffer)
+	{
+		if (buffer.size() < sizeof(uint64_t))
+			return BAN::Error::from_errno(EINVAL);
+
+		while (m_value == 0)
+			TRY(Thread::current().block_or_eintr_indefinite(m_thread_blocker, &m_mutex));
+
+		const uint64_t read_value = m_is_semaphore ? 1 : m_value;
+		m_value -= read_value;
+
+		buffer.as<uint64_t>() = read_value;
+
+		epoll_notify(EPOLLOUT);
+
+		return sizeof(uint64_t);
+	}
+
+	BAN::ErrorOr<size_t> EventFD::write_impl(off_t, BAN::ConstByteSpan buffer)
+	{
+		if (buffer.size() < sizeof(uint64_t))
+			return BAN::Error::from_errno(EINVAL);
+
+		const uint64_t write_value = buffer.as<const uint64_t>();
+		if (write_value == UINT64_MAX)
+			return BAN::Error::from_errno(EINVAL);
+
+		while (m_value + write_value < m_value)
+			TRY(Thread::current().block_or_eintr_indefinite(m_thread_blocker, &m_mutex));
+
+		m_value += write_value;
+
+		if (m_value > 0)
+			epoll_notify(EPOLLIN);
+
+		return sizeof(uint64_t);
+	}
+
+}