tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_nomem.pkt

// SPDX-License-Identifier: GPL-2.0
// When tcp_receive_window() < tcp_max_receive_window(), tcp_sequence() accepts
// packets that would be dropped under normal conditions (i.e. tcp_receive_window()
// equal to tcp_max_receive_window()).
// Test that such packets are handled as expected for RWIN == 0 and for RWIN > 0.

--mss=1000

`./defaults.sh`

    0 `nstat -n`

// Establish a connection.
   +0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1000000], 4) = 0
   +0 bind(3, ..., ...) = 0
   +0 listen(3, 1) = 0

   +0 < S 0:0(0) win 32792 <mss 1000,nop,nop,sackOK,nop,wscale 7>
   +0 > S. 0:0(0) ack 1 win 65535 <mss 1460,nop,nop,sackOK,nop,wscale 4>
   +0 < . 1:1(0) ack 1 win 257

   +0 accept(3, ..., ...) = 4

// Put 1040000 bytes into the receive buffer
   +0 < P. 1:65001(65000) ack 1 win 257
    * > .  1:1(0) ack 65001
   +0 < P. 65001:130001(65000) ack 1 win 257
    * > .  1:1(0) ack 130001
   +0 < P. 130001:195001(65000) ack 1 win 257
    * > .  1:1(0) ack 195001
   +0 < P. 195001:260001(65000) ack 1 win 257
    * > .  1:1(0) ack 260001
   +0 < P. 260001:325001(65000) ack 1 win 257
    * > .  1:1(0) ack 325001
   +0 < P. 325001:390001(65000) ack 1 win 257
    * > .  1:1(0) ack 390001
   +0 < P. 390001:455001(65000) ack 1 win 257
    * > .  1:1(0) ack 455001
   +0 < P. 455001:520001(65000) ack 1 win 257
    * > .  1:1(0) ack 520001
   +0 < P. 520001:585001(65000) ack 1 win 257
    * > .  1:1(0) ack 585001
   +0 < P. 585001:650001(65000) ack 1 win 257
    * > .  1:1(0) ack 650001
   +0 < P. 650001:715001(65000) ack 1 win 257
    * > .  1:1(0) ack 715001
   +0 < P. 715001:780001(65000) ack 1 win 257
    * > .  1:1(0) ack 780001
   +0 < P. 780001:845001(65000) ack 1 win 257
    * > .  1:1(0) ack 845001
   +0 < P. 845001:910001(65000) ack 1 win 257
    * > .  1:1(0) ack 910001
   +0 < P. 910001:975001(65000) ack 1 win 257
    * > .  1:1(0) ack 975001
   +0 < P. 975001:1040001(65000) ack 1 win 257
    * > .  1:1(0) ack 1040001

// Trigger an extreme memory squeeze by shrinking SO_RCVBUF
   +0 setsockopt(4, SOL_SOCKET, SO_RCVBUF, [16000], 4) = 0

   +0 < P. 1040001:1105001(65000) ack 1 win 257
    * > .  1:1(0) ack 1040001 win 0
// Check LINUX_MIB_TCPRCVQDROP has been incremented
   +0 `nstat -s | grep TcpExtTCPRcvQDrop| grep -q " 1 "`

// RWIN == 0: rcv_wup = 1040001, rcv_wnd = 0, rcv_mwnd_seq > 1105001 (significantly larger, typically ~1970000)

// Accept pure ack with seq in max adv. window
   +0 write(4, ..., 1000) = 1000
   +0 > P. 1:1001(1000) ack 1040001 win 0
   +0 < .  1105001:1105001(0) ack 1001 win 257

// In order segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_ZEROWINDOW)
   +0 < P. 1040001:1041001(1000) ack 1001 win 257
   +0 > .  1001:1001(0) ack 1040001 win 0
// Ooo partial segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_ZEROWINDOW)
   +0 < P. 1039001:1041001(2000) ack 1001 win 257
   +0 > .  1001:1001(0) ack 1040001 win 0 <nop,nop,sack 1039001:1040001>
// Check LINUX_MIB_TCPZEROWINDOWDROP has been incremented twice
   +0 `nstat -s | grep TcpExtTCPZeroWindowDrop| grep -q " 2 "`

// Ooo segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_OVERWINDOW)
   +0 < P. 1105001:1106001(1000) ack 1001 win 257
   +0 > .  1001:1001(0) ack 1040001 win 0
// Ooo segment, beyond max adv. window -> drop (SKB_DROP_REASON_TCP_INVALID_SEQUENCE)
   +0 < P. 2000001:2001001(1000) ack 1001 win 257
   +0 > .  1001:1001(0) ack 1040001 win 0
// Check LINUX_MIB_BEYOND_WINDOW has been incremented twice
   +0 `nstat -s | grep TcpExtBeyondWindow | grep -q " 2 "`

// Read all data
   +0 read(4, ..., 2000000) = 1040000
    * > .  1001:1001(0) ack 1040001

// RWIN > 0: rcv_wup = 1040001, 0 < rcv_wnd < 32000, rcv_mwnd_seq > 1105001 (significantly larger, typically ~1970000)

// Accept pure ack with seq in max adv. window, beyond adv. window
   +0 write(4, ..., 1000) = 1000
   +0 > P.  1001:2001(1000) ack 1040001
   +0 < . 1105001:1105001(0) ack 2001 win 257

// In order segment, in max adv. window, in adv. window -> accept
// Note: This also ensures that we cannot hit the empty queue exception in tcp_sequence() in the following tests
   +0 < P. 1040001:1041001(1000) ack 2001 win 257
    * > .  2001:2001(0) ack 1041001

// Ooo partial segment, in adv. window -> accept
   +0 < P. 1040001:1042001(2000) ack 2001 win 257
   +0 > .  2001:2001(0) ack 1042001 <nop,nop,sack 1040001:1041001>

// Ooo segment, in max adv. window, beyond adv. window -> drop (SKB_DROP_REASON_TCP_OVERWINDOW)
   +0 < P. 1105001:1106001(1000) ack 2001 win 257
   +0 > .  2001:2001(0) ack 1042001
// Ooo segment, beyond max adv. window, beyond adv. window -> drop (SKB_DROP_REASON_TCP_INVALID_SEQUENCE)
   +0 < P. 2000001:2001001(1000) ack 2001 win 257
   +0 > .  2001:2001(0) ack 1042001
// Check LINUX_MIB_BEYOND_WINDOW has been incremented twice
   +0 `nstat -s | grep TcpExtBeyondWindow | grep -q " 4 "`

// We are allowed to go beyond the window and buffer with one packet
   +0 < P. 1042001:1062001(20000) ack 2001 win 257
    * > .  2001:2001(0) ack 1062001
   +0 < P. 1062001:1082001(20000) ack 2001 win 257
    * > .  2001:2001(0) ack 1082001 win 0

// But not more: In order segment, in max adv. window -> drop (SKB_DROP_REASON_TCP_ZEROWINDOW)
   +0 < P. 1082001:1083001(1000) ack 2001 win 257
    * > .  2001:2001(0) ack 1082001
// Check LINUX_MIB_TCPZEROWINDOWDROP has been incremented again
   +0 `nstat -s | grep TcpExtTCPZeroWindowDrop| grep -q " 3 "`