Kernel/LibC: Implement basic epoll

This implementation is on top of inodes instead of fds as linux does it.
If I start finding ports/software that relies on epoll allowing
duplicate inodes, I will do what linux does.

I'm probably missing multiple epoll_notify's which may cause hangs but
the system seems to work fine :dd:

kernel/kernel/FS/Inode.cpp

@@ -1,3 +1,4 @@
+#include <kernel/Epoll.h>
 #include <kernel/FS/Inode.h>
 #include <kernel/Lock/LockGuard.h>
 #include <kernel/Memory/FileBackedRegion.h>
@@ -249,10 +250,39 @@ namespace Kernel
 		return has_error_impl();
 	}
 
+	bool Inode::has_hangup() const
+	{
+		LockGuard _(m_mutex);
+		return has_hangup_impl();
+	}
+
 	BAN::ErrorOr<long> Inode::ioctl(int request, void* arg)
 	{
 		LockGuard _(m_mutex);
 		return ioctl_impl(request, arg);
 	}
 
+	BAN::ErrorOr<void> Inode::add_epoll(class Epoll* epoll)
+	{
+		TRY(m_epolls.push_back(epoll));
+		return {};
+	}
+
+	void Inode::del_epoll(class Epoll* epoll)
+	{
+		for (auto it = m_epolls.begin(); it != m_epolls.end(); it++)
+		{
+			if (*it != epoll)
+				continue;
+			m_epolls.remove(it);
+			break;
+		}
+	}
+
+	void Inode::epoll_notify(uint32_t event)
+	{
+		for (auto* epoll : m_epolls)
+			epoll->notify(this, event);
+	}
+
 }

kernel/kernel/FS/Pipe.cpp

@@ -3,7 +3,7 @@
 #include <kernel/Thread.h>
 #include <kernel/Timer/Timer.h>
 
-#include <kernel/Process.h>
+#include <sys/epoll.h>
 
 namespace Kernel
 {
@@ -36,8 +36,10 @@ namespace Kernel
 	{
 		auto old_writing_count = m_writing_count.fetch_sub(1);
 		ASSERT(old_writing_count > 0);
-		if (old_writing_count == 1)
-			m_thread_blocker.unblock();
+		if (old_writing_count != 1)
+			return;
+		epoll_notify(EPOLLHUP);
+		m_thread_blocker.unblock();
 	}
 
 	BAN::ErrorOr<size_t> Pipe::read_impl(off_t, BAN::ByteSpan buffer)
@@ -69,6 +71,8 @@ namespace Kernel
 
 		m_atime = SystemTimer::get().real_time();
 
+		epoll_notify(EPOLLOUT);
+
 		m_thread_blocker.unblock();
 
 		return to_copy;
@@ -103,6 +107,8 @@ namespace Kernel
 		m_mtime = current_time;
 		m_ctime = current_time;
 
+		epoll_notify(EPOLLIN);
+
 		m_thread_blocker.unblock();
 
 		return to_copy;

kernel/kernel/FS/TmpFS/Inode.cpp

@@ -226,7 +226,6 @@ namespace Kernel
 	}
 
 	/* SOCKET INODE */
-
 	BAN::ErrorOr<BAN::RefPtr<TmpSocketInode>> TmpSocketInode::create_new(TmpFileSystem& fs, mode_t mode, uid_t uid, gid_t gid)
 	{
 		auto info = create_inode_info(Mode::IFSOCK | mode, uid, gid);