Kernel: Make local socket descriptor allocations more efficient

Now we only track the numerical fd, whereas previously we also tracked
the respective OpenFileDescription instance. This patch also gives the
vector in sys$recvmsg some inline capacity to reduce allocation churn.

Kernel/Net/LocalSocket.cpp

@@ -535,10 +535,9 @@ ErrorOr<NonnullRefPtr<OpenFileDescription>> LocalSocket::recvfd(OpenFileDescript
     return queue.take_first();
 }
 
-ErrorOr<Vector<NonnullRefPtr<OpenFileDescription>>> LocalSocket::recvfds(OpenFileDescription const& socket_description, int n)
+ErrorOr<void> LocalSocket::recvfds(OpenFileDescription const& socket_description, int n, Function<ErrorOr<void>(OpenFileDescription&)> callback)
 {
     MutexLocker locker(mutex());
-    Vector<NonnullRefPtr<OpenFileDescription>> fds;
 
     auto role = this->role(socket_description);
     if (role != Role::Connected && role != Role::Accepted)
@@ -549,10 +548,10 @@ ErrorOr<Vector<NonnullRefPtr<OpenFileDescription>>> LocalSocket::recvfds(OpenFil
         if (queue.is_empty())
             break;
 
-        fds.append(queue.take_first());
+        TRY(callback(*queue.take_first()));
     }
 
-    return fds;
+    return {};
 }
 
 ErrorOr<void> LocalSocket::try_set_path(StringView path)

Kernel/Net/LocalSocket.h

@@ -29,7 +29,7 @@ public:
 
     ErrorOr<void> sendfd(OpenFileDescription const& socket_description, NonnullRefPtr<OpenFileDescription> passing_description);
     ErrorOr<NonnullRefPtr<OpenFileDescription>> recvfd(OpenFileDescription const& socket_description);
-    ErrorOr<Vector<NonnullRefPtr<OpenFileDescription>>> recvfds(OpenFileDescription const& socket_description, int n);
+    ErrorOr<void> recvfds(OpenFileDescription const& socket_description, int n, Function<ErrorOr<void>(OpenFileDescription&)> callback);
 
     static void for_each(Function<void(LocalSocket const&)>);
     static ErrorOr<void> try_for_each(Function<ErrorOr<void>(LocalSocket const&)>);

Kernel/Syscalls/socket.cpp

@@ -317,13 +317,12 @@ ErrorOr<FlatPtr> Process::sys$recvmsg(int sockfd, Userspace<struct msghdr*> user
     int space_for_fds = (msg.msg_controllen - current_cmsg_len - sizeof(struct cmsghdr)) / sizeof(int);
     if (space_for_fds > 0 && socket.is_local()) {
         auto& local_socket = static_cast<LocalSocket&>(socket);
-        auto descriptions = TRY(local_socket.recvfds(description, space_for_fds));
-        Vector<int> fdnums;
-        for (auto& description : descriptions) {
+        Vector<int, 128> fdnums;
+        TRY(local_socket.recvfds(description, space_for_fds, [&](auto const& description) -> ErrorOr<void> {
             auto fd_allocation = TRY(m_fds.with_exclusive([](auto& fds) { return fds.allocate(); }));
-            m_fds.with_exclusive([&](auto& fds) { fds[fd_allocation.fd].set(*description, 0); });
-            fdnums.append(fd_allocation.fd);
-        }
+            m_fds.with_exclusive([&](auto& fds) { fds[fd_allocation.fd].set(description, 0); });
+            return fdnums.try_append(fd_allocation.fd);
+        }));
         if (!fdnums.is_empty())
             TRY(try_add_cmsg(SOL_SOCKET, SCM_RIGHTS, fdnums.data(), fdnums.size() * sizeof(int)));
     }