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Kernel: Add support for TCP window size scaling

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This should allow us to eventually properly saturate high-bandwidth
network links when using TCP, once other nonoptimal parts of our
network stack are improved.
This commit is contained in:
Idan Horowitz 2023-12-26 21:05:15 +02:00 • committed by Andreas Kling
parent 2c51ff763b
commit 785c9d5c2b
6 changed files with 124 additions and 14 deletions
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30
Kernel/Net/TCPSocket.cpp
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@ -245,10 +245,11 @@ ErrorOr<void> TCPSocket::send_tcp_packet(u16 flags, UserOrKernelBuffer const* pa
auto ipv4_payload_offset = routing_decision.adapter->ipv4_payload_offset();
bool const has_mss_option = flags == TCPFlags::SYN;
const size_t options_size = has_mss_option ? sizeof(TCPOptionMSS) : 0;
const size_t tcp_header_size = sizeof(TCPPacket) + options_size;
const size_t buffer_size = ipv4_payload_offset + tcp_header_size + payload_size;
bool const has_mss_option = flags & TCPFlags::SYN;
bool const has_window_scale_option = flags & TCPFlags::SYN;
size_t const options_size = (has_mss_option ? sizeof(TCPOptionMSS) : 0) + (has_window_scale_option ? sizeof(TCPOptionWindowScale) : 0);
size_t const tcp_header_size = sizeof(TCPPacket) + align_up_to(options_size, 4);
size_t const buffer_size = ipv4_payload_offset + tcp_header_size + payload_size;
auto packet = routing_decision.adapter->acquire_packet_buffer(buffer_size);
if (!packet)
return set_so_error(ENOMEM);
@ -260,7 +261,10 @@ ErrorOr<void> TCPSocket::send_tcp_packet(u16 flags, UserOrKernelBuffer const* pa
VERIFY(local_port());
tcp_packet.set_source_port(local_port());
tcp_packet.set_destination_port(peer_port());
tcp_packet.set_window_size(min(available_space_in_receive_buffer(), NumericLimits<u16>::max()));
auto window_size = available_space_in_receive_buffer();
if ((flags & TCPFlags::SYN) == 0 && m_window_scaling_supported)
window_size >>= receive_window_scale();
tcp_packet.set_window_size(min(window_size, NumericLimits<u16>::max()));
tcp_packet.set_sequence_number(m_sequence_number);
tcp_packet.set_data_offset(tcp_header_size / sizeof(u32));
tcp_packet.set_flags(flags);
@ -284,12 +288,20 @@ ErrorOr<void> TCPSocket::send_tcp_packet(u16 flags, UserOrKernelBuffer const* pa
m_sequence_number += payload_size;
}
u8* next_option = packet->buffer->data() + ipv4_payload_offset + sizeof(TCPPacket);
if (has_mss_option) {
u16 mss = routing_decision.adapter->mtu() - sizeof(IPv4Packet) - sizeof(TCPPacket);
TCPOptionMSS mss_option { mss };
VERIFY(packet->buffer->size() >= ipv4_payload_offset + sizeof(TCPPacket) + sizeof(mss_option));
memcpy(packet->buffer->data() + ipv4_payload_offset + sizeof(TCPPacket), &mss_option, sizeof(mss_option));
memcpy(next_option, &mss_option, sizeof(mss_option));
next_option += sizeof(mss_option);
}
if (has_window_scale_option) {
TCPOptionWindowScale window_scale_option { receive_window_scale() };
memcpy(next_option, &window_scale_option, sizeof(window_scale_option));
next_option += sizeof(window_scale_option);
}
if ((options_size % 4) != 0)
*next_option = to_underlying(TCPOptionKind::End);
tcp_packet.set_checksum(compute_tcp_checksum(local_address(), peer_address(), tcp_packet, payload_size));
@ -339,7 +351,7 @@ void TCPSocket::receive_tcp_packet(TCPPacket const& packet, u16 size)
old_adapter->release_packet_buffer(*packet.buffer);
TCPPacket& tcp_packet = *(TCPPacket*)(packet.buffer->buffer->data() + packet.ipv4_payload_offset);
if (m_send_window_size != tcp_packet.window_size()) {
m_send_window_size = tcp_packet.window_size();
m_send_window_size = tcp_packet.window_size() << m_send_window_scale;
}
auto payload_size = packet.buffer->buffer->data() + packet.buffer->buffer->size() - (u8*)tcp_packet.payload();
unacked_packets.size -= payload_size;
@ -367,7 +379,7 @@ void TCPSocket::receive_tcp_packet(TCPPacket const& packet, u16 size)
bool TCPSocket::should_delay_next_ack() const
{
// FIXME: We don't know the MSS here so make a reasonable guess.
const size_t mss = 1500;
size_t const mss = 1500;
// RFC 1122 says we should send an ACK for every two full-sized segments.
if (m_ack_number >= m_last_ack_number_sent + 2 * mss)