socket: Add support for TCP defer accept
TCP_DEFER_ACCEPT Allow a listener to be awakened only when data arrives on the socket. If TCP_DEFER_ACCEPT set on a server-side listening socket, the TCP/IP stack will not to wait for the final ACK packet and not to initiate the process until the first packet of real data has arrived. After sending the SYN/ACK, the server will then wait for a data packet from a client. Now, only three packets will be sent over the network, and the connection establishment delay will be significantly reduced.
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@ -545,6 +545,47 @@
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for details.).</para></listitem>
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for details.).</para></listitem>
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</varlistentry>
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</varlistentry>
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<varlistentry>
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<term><varname>DeferAccept=</varname></term>
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<listitem><para>Takes time (in
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seconds) as argument. If set, the
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listening process will be awakened
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only when data arrives on the socket,
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and not immediately when connection is
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established. When this option is set,
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the
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<constant>TCP_DEFER_ACCEPT</constant>
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socket option will be used (see
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<citerefentry><refentrytitle>tcp</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
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and the kernel will ignore initial ACK
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packets without any data. The argument
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specifies the approximate amount of
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time the kernel should wait for
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incoming data before falling back to
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the normal behaviour of honouring
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empty ACK packets. This option is
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beneficial for protocols where the
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client sends the data first (e.g.
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HTTP, in contrast to SMTP), because
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the server process will not be woken
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up unnecessarily before it can take
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any action.
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</para>
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<para>If the client also uses the
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<constant>TCP_DEFER_ACCEPT</constant>
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option, the latency of the initial
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connection may be reduced, because the
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kernel will send data in the final
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packet establishing the connection
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(the third packet in the "three-way
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handshake").</para>
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<para>Disabled by default.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<varlistentry>
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<term><varname>ReceiveBuffer=</varname></term>
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<term><varname>ReceiveBuffer=</varname></term>
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<term><varname>SendBuffer=</varname></term>
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<term><varname>SendBuffer=</varname></term>
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@ -100,6 +100,7 @@ const sd_bus_vtable bus_socket_vtable[] = {
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SD_BUS_PROPERTY("KeepAliveTime", "t", bus_property_get_usec, offsetof(Socket, keep_alive_time), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("KeepAliveTime", "t", bus_property_get_usec, offsetof(Socket, keep_alive_time), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("KeepAliveInterval", "t", bus_property_get_usec, offsetof(Socket, keep_alive_interval), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("KeepAliveInterval", "t", bus_property_get_usec, offsetof(Socket, keep_alive_interval), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("KeepAliveProbes", "u", bus_property_get_unsigned, offsetof(Socket, keep_alive_cnt), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("KeepAliveProbes", "u", bus_property_get_unsigned, offsetof(Socket, keep_alive_cnt), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("DeferAccept" , "t", bus_property_get_usec, offsetof(Socket, defer_accept), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("Priority", "i", bus_property_get_int, offsetof(Socket, priority), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("Priority", "i", bus_property_get_int, offsetof(Socket, priority), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("ReceiveBuffer", "t", bus_property_get_size, offsetof(Socket, receive_buffer), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("ReceiveBuffer", "t", bus_property_get_size, offsetof(Socket, receive_buffer), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("SendBuffer", "t", bus_property_get_size, offsetof(Socket, send_buffer), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("SendBuffer", "t", bus_property_get_size, offsetof(Socket, send_buffer), SD_BUS_VTABLE_PROPERTY_CONST),
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@ -234,6 +234,7 @@ Socket.KeepAlive, config_parse_bool, 0,
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Socket.KeepAliveTime, config_parse_sec, 0, offsetof(Socket, keep_alive_time)
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Socket.KeepAliveTime, config_parse_sec, 0, offsetof(Socket, keep_alive_time)
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Socket.KeepAliveInterval, config_parse_sec, 0, offsetof(Socket, keep_alive_interval)
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Socket.KeepAliveInterval, config_parse_sec, 0, offsetof(Socket, keep_alive_interval)
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Socket.KeepAliveProbes, config_parse_unsigned, 0, offsetof(Socket, keep_alive_cnt)
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Socket.KeepAliveProbes, config_parse_unsigned, 0, offsetof(Socket, keep_alive_cnt)
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Socket.DeferAccept, config_parse_sec, 0, offsetof(Socket, defer_accept)
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Socket.NoDelay, config_parse_bool, 0, offsetof(Socket, no_delay)
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Socket.NoDelay, config_parse_bool, 0, offsetof(Socket, no_delay)
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Socket.Priority, config_parse_int, 0, offsetof(Socket, priority)
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Socket.Priority, config_parse_int, 0, offsetof(Socket, priority)
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Socket.ReceiveBuffer, config_parse_iec_size, 0, offsetof(Socket, receive_buffer)
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Socket.ReceiveBuffer, config_parse_iec_size, 0, offsetof(Socket, receive_buffer)
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@ -613,6 +613,12 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) {
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"%sKeepAliveProbes: %u\n",
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"%sKeepAliveProbes: %u\n",
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prefix, s->keep_alive_cnt);
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prefix, s->keep_alive_cnt);
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if(s->defer_accept)
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fprintf(f,
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"%sDeferAccept: %s\n",
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prefix, format_timespan(time_string, FORMAT_TIMESPAN_MAX,
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s->defer_accept, USEC_PER_SEC));
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LIST_FOREACH(port, p, s->ports) {
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LIST_FOREACH(port, p, s->ports) {
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if (p->type == SOCKET_SOCKET) {
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if (p->type == SOCKET_SOCKET) {
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@ -828,6 +834,12 @@ static void socket_apply_socket_options(Socket *s, int fd) {
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log_warning_unit(UNIT(s)->id, "TCP_KEEPCNT failed: %m");
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log_warning_unit(UNIT(s)->id, "TCP_KEEPCNT failed: %m");
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}
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}
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if (s->defer_accept) {
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int value = s->defer_accept / USEC_PER_SEC;
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if (setsockopt(fd, SOL_TCP, TCP_DEFER_ACCEPT, &value, sizeof(value)) < 0)
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log_warning_unit(UNIT(s)->id, "TCP_DEFER_ACCEPT failed: %m");
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}
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if (s->no_delay) {
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if (s->no_delay) {
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int b = s->no_delay;
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int b = s->no_delay;
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if (setsockopt(fd, SOL_TCP, TCP_NODELAY, &b, sizeof(b)) < 0)
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if (setsockopt(fd, SOL_TCP, TCP_NODELAY, &b, sizeof(b)) < 0)
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@ -105,6 +105,7 @@ struct Socket {
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usec_t timeout_usec;
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usec_t timeout_usec;
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usec_t keep_alive_time;
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usec_t keep_alive_time;
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usec_t keep_alive_interval;
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usec_t keep_alive_interval;
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usec_t defer_accept;
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ExecCommand* exec_command[_SOCKET_EXEC_COMMAND_MAX];
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ExecCommand* exec_command[_SOCKET_EXEC_COMMAND_MAX];
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ExecContext exec_context;
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ExecContext exec_context;
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