Kernel: Allow File::close() to fail

And pass the result through to sys$close() return value.

Fixes https://github.com/SerenityOS/serenity/issues/427

Kernel/Net/IPv4Socket.cpp

@@ -564,9 +564,10 @@ int IPv4Socket::ioctl(FileDescription&, unsigned request, FlatPtr arg)
     return -EINVAL;
 }
 
-void IPv4Socket::close()
+KResult IPv4Socket::close()
 {
-    shutdown(SHUT_RDWR);
+    (void)shutdown(SHUT_RDWR);
+    return KSuccess;
 }
 
 void IPv4Socket::shut_down_for_reading()

Kernel/Net/IPv4Socket.h

@@ -48,7 +48,7 @@ public:
 
     static Lockable<HashTable<IPv4Socket*>>& all_sockets();
 
-    virtual void close() override;
+    virtual KResult close() override;
     virtual KResult bind(const sockaddr*, socklen_t) override;
     virtual KResult connect(FileDescription&, const sockaddr*, socklen_t, ShouldBlock = ShouldBlock::Yes) override;
     virtual KResult listen(size_t) override;

Kernel/Net/TCPSocket.cpp

@@ -440,9 +440,9 @@ void TCPSocket::shut_down_for_writing()
     }
 }
 
-void TCPSocket::close()
+KResult TCPSocket::close()
 {
-    IPv4Socket::close();
+    auto result = IPv4Socket::close();
     if (state() == State::CloseWait) {
 #ifdef TCP_SOCKET_DEBUG
         dbg() << " Sending FIN from CloseWait and moving into LastAck";
@@ -453,6 +453,7 @@ void TCPSocket::close()
 
     LOCKER(closing_sockets().lock());
     closing_sockets().resource().set(tuple(), *this);
+    return result;
 }
 
 }

Kernel/Net/TCPSocket.h

@@ -165,7 +165,7 @@ public:
     void release_to_originator();
     void release_for_accept(RefPtr<TCPSocket>);
 
-    virtual void close() override;
+    virtual KResult close() override;
 
 protected:
     void set_direction(Direction direction) { m_direction = direction; }