kernel/linux.git/include/uapi/linux/tcp.h, branch v6.19.11

tcp: accecn: AccECN option failure handling

2025-09-18T06:47:52+00:00

AccECN option may fail in various way, handle these: - Attempt to negotiate the use of AccECN on the 1st retransmitted SYN - From the 2nd retransmitted SYN, stop AccECN negotiation - Remove option from SYN/ACK rexmits to handle blackholes - If no option arrives in SYN/ACK, assume Option is not usable - If an option arrives later, re-enabled - If option is zeroed, disable AccECN option processing This patch use existing padding bits in tcp_request_sock and holes in tcp_sock without increasing the size. Signed-off-by: Ilpo Järvinen Signed-off-by: Chia-Yu Chang Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250916082434.100722-9-chia-yu.chang@nokia-bell-labs.com Signed-off-by: Paolo Abeni

tcp: accecn: AccECN option

2025-09-18T06:47:52+00:00

The Accurate ECN allows echoing back the sum of bytes for each IP ECN field value in the received packets using AccECN option. This change implements AccECN option tx & rx side processing without option send control related features that are added by a later change. Based on specification: https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-28.txt (Some features of the spec will be added in the later changes rather than in this one). A full-length AccECN option is always attempted but if it does not fit, the minimum length is selected based on the counters that have changed since the last update. The AccECN option (with 24-bit fields) often ends in odd sizes so the option write code tries to take advantage of some nop used to pad the other TCP options. The delivered_ecn_bytes pairs with received_ecn_bytes similar to how delivered_ce pairs with received_ce. In contrast to ACE field, however, the option is not always available to update delivered_ecn_bytes. For ACK w/o AccECN option, the delivered bytes calculated based on the cumulative ACK+SACK information are assigned to one of the counters using an estimation heuristic to select the most likely ECN byte counter. Any estimation error is corrected when the next AccECN option arrives. It may occur that the heuristic gets too confused when there are enough different byte counter deltas between ACKs with the AccECN option in which case the heuristic just gives up on updating the counters for a while. tcp_ecn_option sysctl can be used to select option sending mode for AccECN: TCP_ECN_OPTION_DISABLED, TCP_ECN_OPTION_MINIMUM, and TCP_ECN_OPTION_FULL. This patch increases the size of tcp_info struct, as there is no existing holes for new u32 variables. Below are the pahole outcomes before and after this patch: [BEFORE THIS PATCH] struct tcp_info { [...] __u32 tcpi_total_rto_time; /* 244 4 */ /* size: 248, cachelines: 4, members: 61 */ } [AFTER THIS PATCH] struct tcp_info { [...] __u32 tcpi_total_rto_time; /* 244 4 */ __u32 tcpi_received_ce; /* 248 4 */ __u32 tcpi_delivered_e1_bytes; /* 252 4 */ __u32 tcpi_delivered_e0_bytes; /* 256 4 */ __u32 tcpi_delivered_ce_bytes; /* 260 4 */ __u32 tcpi_received_e1_bytes; /* 264 4 */ __u32 tcpi_received_e0_bytes; /* 268 4 */ __u32 tcpi_received_ce_bytes; /* 272 4 */ /* size: 280, cachelines: 5, members: 68 */ } This patch uses the existing 1-byte holes in the tcp_sock_write_txrx group for new u8 members, but adds a 4-byte hole in tcp_sock_write_rx group after the new u32 delivered_ecn_bytes[3] member. Therefore, the group size of tcp_sock_write_rx is increased from 96 to 112. Below are the pahole outcomes before and after this patch: [BEFORE THIS PATCH] struct tcp_sock { [...] u8 received_ce_pending:4; /* 2522: 0 1 */ u8 unused2:4; /* 2522: 4 1 */ /* XXX 1 byte hole, try to pack */ [...] u32 rcv_rtt_last_tsecr; /* 2668 4 */ [...] __cacheline_group_end__tcp_sock_write_rx[0]; /* 2728 0 */ [...] /* size: 3200, cachelines: 50, members: 167 */ } [AFTER THIS PATCH] struct tcp_sock { [...] u8 received_ce_pending:4;/* 2522: 0 1 */ u8 unused2:4; /* 2522: 4 1 */ u8 accecn_minlen:2; /* 2523: 0 1 */ u8 est_ecnfield:2; /* 2523: 2 1 */ u8 unused3:4; /* 2523: 4 1 */ [...] u32 rcv_rtt_last_tsecr; /* 2668 4 */ u32 delivered_ecn_bytes[3];/* 2672 12 */ /* XXX 4 bytes hole, try to pack */ [...] __cacheline_group_end__tcp_sock_write_rx[0]; /* 2744 0 */ [...] /* size: 3200, cachelines: 50, members: 171 */ } Signed-off-by: Ilpo Järvinen Signed-off-by: Neal Cardwell Co-developed-by: Chia-Yu Chang Signed-off-by: Chia-Yu Chang Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250916082434.100722-7-chia-yu.chang@nokia-bell-labs.com Signed-off-by: Paolo Abeni

tcp: fastopen: pass TFO child indication through getsockopt

2025-04-25T01:21:04+00:00

tcp: fastopen: pass TFO child indication through getsockopt Note that this uses up the last bit of a field in struct tcp_info Signed-off-by: Jeremy Harris Reviewed-by: Eric Dumazet Reviewed-by: Neal Cardwell Link: https://patch.msgid.link/20250423124334.4916-3-jgh@exim.org Signed-off-by: Jakub Kicinski

tcp: support TCP_DELACK_MAX_US for set/getsockopt use

2025-03-25T11:27:20+00:00

Support adjusting/reading delayed ack max for socket level by using set/getsockopt(). This option aligns with TCP_BPF_DELACK_MAX usage. Considering that bpf option was implemented before this patch, so we need to use a standalone new option for pure tcp set/getsockopt() use. Add WRITE_ONCE/READ_ONCE() to prevent data-race if setsockopt() happens to write one value to icsk_delack_max while icsk_delack_max is being read. Signed-off-by: Jason Xing Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250317120314.41404-3-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski

tcp: support TCP_RTO_MIN_US for set/getsockopt use

2025-03-25T11:27:19+00:00

Support adjusting/reading RTO MIN for socket level by using set/getsockopt(). This new option has the same effect as TCP_BPF_RTO_MIN, which means it doesn't affect RTAX_RTO_MIN usage (by using ip route...). Considering that bpf option was implemented before this patch, so we need to use a standalone new option for pure tcp set/getsockopt() use. When the socket is created, its icsk_rto_min is set to the default value that is controlled by sysctl_tcp_rto_min_us. Then if application calls setsockopt() with TCP_RTO_MIN_US flag to pass a valid value, then icsk_rto_min will be overridden in jiffies unit. This patch adds WRITE_ONCE/READ_ONCE to avoid data-race around icsk_rto_min. Signed-off-by: Jason Xing Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250317120314.41404-2-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski

tcp: extend TCP flags to allow AE bit/ACE field

2025-03-17T13:49:46+00:00

With AccECN, there's one additional TCP flag to be used (AE) and ACE field that overloads the definition of AE, CWR, and ECE flags. As tcp_flags was previously only 1 byte, the byte-order stuff needs to be added to it's handling. Signed-off-by: Ilpo Järvinen Signed-off-by: Chia-Yu Chang Reviewed-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: add the ability to control max RTO

2025-02-11T12:08:00+00:00

Currently, TCP stack uses a constant (120 seconds) to limit the RTO value exponential growth. Some applications want to set a lower value. Add TCP_RTO_MAX_MS socket option to set a value (in ms) between 1 and 120 seconds. It is discouraged to change the socket rto max on a live socket, as it might lead to unexpected disconnects. Following patch is adding a netns sysctl to control the default value at socket creation time. Signed-off-by: Eric Dumazet Reviewed-by: Jason Xing Reviewed-by: Neal Cardwell Reviewed-by: Kuniyuki Iwashima Signed-off-by: Paolo Abeni

tcp: socket option to check for MPTCP fallback to TCP

2024-05-13T21:48:04+00:00

A way for an application to know if an MPTCP connection fell back to TCP is to use getsockopt(MPTCP_INFO) and look for errors. The issue with this technique is that the same errors -- EOPNOTSUPP (IPv4) and ENOPROTOOPT (IPv6) -- are returned if there was a fallback, *or* if the kernel doesn't support this socket option. The userspace then has to look at the kernel version to understand what the errors mean. It is not clean, and it doesn't take into account older kernels where the socket option has been backported. A cleaner way would be to expose this info to the TCP socket level. In case of MPTCP socket where no fallback happened, the socket options for the TCP level will be handled in MPTCP code, in mptcp_getsockopt_sol_tcp(). If not, that will be in TCP code, in do_tcp_getsockopt(). So MPTCP simply has to set the value 1, while TCP has to set 0. If the socket option is not supported, one of these two errors will be reported: - EOPNOTSUPP (95 - Operation not supported) for MPTCP sockets - ENOPROTOOPT (92 - Protocol not available) for TCP sockets, e.g. on the socket received after an 'accept()', when the client didn't request to use MPTCP: this socket will be a TCP one, even if the listen socket was an MPTCP one. With this new option, the kernel can return a clear answer to both "Is this kernel new enough to tell me the fallback status?" and "If it is new enough, is it currently a TCP or MPTCP socket?" questions, while not breaking the previous method. Acked-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://lore.kernel.org/r/20240509-upstream-net-next-20240509-mptcp-tcp_is_mptcp-v1-1-f846df999202@kernel.org Signed-off-by: Jakub Kicinski

net/tcp: Add TCP_AO_REPAIR

2023-10-27T09:35:46+00:00

Add TCP_AO_REPAIR setsockopt(), getsockopt(). They let a user to repair TCP-AO ISNs/SNEs. Also let the user hack around when (tp->repair) is on and add ao_info on a socket in any supported state. As SNEs now can be read/written at any moment, use WRITE_ONCE()/READ_ONCE() to set/read them. Signed-off-by: Dmitry Safonov Acked-by: David Ahern Signed-off-by: David S. Miller

net/tcp: Allow asynchronous delete for TCP-AO keys (MKTs)

2023-10-27T09:35:45+00:00

Delete becomes very, very fast - almost free, but after setsockopt() syscall returns, the key is still alive until next RCU grace period. Which is fine for listen sockets as userspace needs to be aware of setsockopt(TCP_AO) and accept() race and resolve it with verification by getsockopt() after TCP connection was accepted. The benchmark results (on non-loaded box, worse with more RCU work pending): > ok 33 Worst case delete 16384 keys: min=5ms max=10ms mean=6.93904ms stddev=0.263421 > ok 34 Add a new key 16384 keys: min=1ms max=4ms mean=2.17751ms stddev=0.147564 > ok 35 Remove random-search 16384 keys: min=5ms max=10ms mean=6.50243ms stddev=0.254999 > ok 36 Remove async 16384 keys: min=0ms max=0ms mean=0.0296107ms stddev=0.0172078 Co-developed-by: Francesco Ruggeri Signed-off-by: Francesco Ruggeri Co-developed-by: Salam Noureddine Signed-off-by: Salam Noureddine Signed-off-by: Dmitry Safonov Acked-by: David Ahern Signed-off-by: David S. Miller