January 2026 - dev

[PATCH v3 00/11] Introduce multiple addresses
by Jon Maloy 09 Feb '26

09 Feb '26

This version contains what I perceive as the least controversial parts of my previous RFC series. It basically makes address handling behave like before, but now allowing multiple addresses both at the host side and the guest side. v2: - Added the earlier standalone CIDR commit to the head of the series. - Replaced the guest namespace interface subscriptions with just an address observation feature, so that it works with both PASTA and PASST. - Unified 'no_copy_addrs' and 'copy_addrs' code paths, as suggested by David G. - Multiple other changes, also based on feedback from David. - Removed the host interface subscription patches, -for now. I intend to re-add them once this series is applied. - Outstanding question: When do we add an IPv4 link local address to the guest? Only in local/opaque mode? Only when explicitly requested? Always? v3: - Unified the IPv4 and IPv6 arrays into one array - Changed prefix_len to always eb in IPv6/IpV4 mapped format - Updated migration protocol to v3, handling multiple addresses - Many other smaller changes, based on feedback from the PASST team Jon Maloy (11): conf: Support CIDR notation for -a/--address option ip: Add IN4_MASK() macro for IPv4 netmask calculation ip: Introduce unified multi-address data structures fwd: Check all configured addresses in guest accessibility functions arp: Check all configured addresses in ARP filtering pasta: Extract pasta_ns_conf_ip4/6() to reduce nesting conf: Allow multiple -a/--address options per address family migrate: Rename v1 address functions to v2 for clarity ip: Track observed guest IPv4 addresses in unified address array ip: Track observed guest IPv6 addresses in unified address array conf: Select addresses for DHCP and NDP distribution arp.c | 17 ++-- conf.c | 249 ++++++++++++++++++++++++++++++++---------------------- conf.h | 6 ++ dhcp.c | 23 +++-- dhcp.h | 2 +- dhcpv6.c | 23 +++-- dhcpv6.h | 2 +- fwd.c | 216 ++++++++++++++++++++++++++++++++++++++-------- fwd.h | 6 ++ inany.c | 68 +++++++++++++++ inany.h | 1 + ip.c | 22 +++++ ip.h | 9 ++ migrate.c | 244 ++++++++++++++++++++++++++++++++++++++++++++++++---- ndp.c | 19 +++-- ndp.h | 4 +- passt.1 | 17 ++-- passt.h | 134 ++++++++++++++++++++++++++--- pasta.c | 197 ++++++++++++++++++++++++------------------ tap.c | 117 +++++++++++++++++++++---- 20 files changed, 1080 insertions(+), 296 deletions(-) -- 2.52.0

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[PATCH 0/1] migrate: Eliminate listening_sock field from TCP connection state
by David Gibson 09 Feb '26

09 Feb '26

A bunch of the things I'm working on right now are made more difficult by the lack of spare space in the TCP connection structure (without adding an additional cache line). I realised that even the minimal forwarding table implementation we have now allows at least one easy win though: the listening_sock field can be eliminated pretty easily. David Gibson (1): migrate: Use forward table information to close() listening sockets flow.c | 12 ++++++++++++ fwd.c | 21 +++++++++++++++++++++ fwd.h | 1 + tcp.c | 9 --------- tcp_conn.h | 3 --- 5 files changed, 34 insertions(+), 12 deletions(-) -- 2.52.0

2 7

[PATCH v2 0/3] Fix errors in FIN timeout logic
by David Gibson 31 Jan '26

31 Jan '26

While investigating bug 179, I found a number of things that confused me about the TCP timer handling. One of them, I think I figured out what's going on and what should be done about it. So, here are the changes. This is mostly about FIN handling and only tangentially about the timer, but it does at least slightly simplify the timer handling while I figure out the rest of it. Changes in v2: * Stefano pointed out some errors in my guesses at the history of things, evised commit message of 2/3 accordingly * Added 3/3 checking for shutdown(2) failures David Gibson (3): tcp: Retransmit FINs like data segments tcp: Eliminate FIN_TIMEOUT tcp, tcp_splice: Check for failures of shutdown(2) tcp.c | 49 ++++++++++++++++++++++++------------------------- tcp_buf.c | 1 + tcp_splice.c | 3 ++- tcp_vu.c | 1 + 4 files changed, 28 insertions(+), 26 deletions(-) -- 2.52.0

2 2

[PATCH v2 3/3] tcp, tcp_splice: Check for failures of shutdown(2)
by David Gibson 30 Jan '26

30 Jan '26

shutdown(2) should never fail, unless we give it bad parameters (e.g. passing it an fd which isn't a connected socket). However, if it ever did, we'd currently ignore the error and carry on which could lead to very confusing behaviour. In the interests of debugability, check for failure of shutdown(2), log an error and: - during runtime, reset the affected connection - during migration, fail the migration Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- tcp.c | 31 ++++++++++++++++++++++++------- tcp_splice.c | 3 ++- 2 files changed, 26 insertions(+), 8 deletions(-) diff --git a/tcp.c b/tcp.c index 0be871a4..9dd02cd8 100644 --- a/tcp.c +++ b/tcp.c @@ -2284,7 +2284,11 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af, if (th->fin) { conn->seq_from_tap++; - shutdown(conn->sock, SHUT_WR); + if (shutdown(conn->sock, SHUT_WR) < 0) { + flow_dbg_perror(conn, "shutdown() failed"); + goto reset; + } + tcp_send_flag(c, conn, ACK); conn_event(c, conn, SOCK_FIN_SENT); @@ -2359,7 +2363,11 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af, socklen_t sl; struct tcp_info tinfo; - shutdown(conn->sock, SHUT_WR); + if (shutdown(conn->sock, SHUT_WR) < 0) { + flow_dbg_perror(conn, "shutdown() failed"); + goto reset; + } + conn_event(c, conn, SOCK_FIN_SENT); tcp_send_flag(c, conn, ACK); ack_due = 0; @@ -3831,10 +3839,15 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd int v; v = TCP_SEND_QUEUE; - if (setsockopt(s, SOL_TCP, TCP_REPAIR_QUEUE, &v, sizeof(v))) + if (setsockopt(s, SOL_TCP, TCP_REPAIR_QUEUE, &v, sizeof(v))) { flow_perror(conn, "Selecting repair queue"); - else - shutdown(s, SHUT_WR); + } else { + if (shutdown(s, SHUT_WR) < 0) { + flow_perror(conn, + "Repair mode shutdown() failed"); + goto fail; + } + } } if (tcp_flow_repair_wnd(conn, &t)) @@ -3861,8 +3874,12 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd * Call shutdown(x, SHUT_WR) *not* in repair mode, which moves us to * TCP_FIN_WAIT1. */ - if (t.tcpi_state == TCP_FIN_WAIT1) - shutdown(s, SHUT_WR); + if (t.tcpi_state == TCP_FIN_WAIT1) { + if (shutdown(s, SHUT_WR) < 0) { + flow_perror(conn, "Post-repair shutdown() failed"); + goto fail; + } + } if (tcp_set_peek_offset(conn, peek_offset)) goto fail; diff --git a/tcp_splice.c b/tcp_splice.c index 8806523a..d60981ca 100644 --- a/tcp_splice.c +++ b/tcp_splice.c @@ -627,7 +627,8 @@ retry: flow_foreach_sidei(sidei) { if ((conn->events & FIN_RCVD(sidei)) && !(conn->events & FIN_SENT(!sidei))) { - shutdown(conn->s[!sidei], SHUT_WR); + if (shutdown(conn->s[!sidei], SHUT_WR) < 0) + goto reset; conn_event(conn, FIN_SENT(!sidei)); } } -- 2.52.0

1 0

[PATCH v2 1/3] tcp: Retransmit FINs like data segments
by David Gibson 30 Jan '26

30 Jan '26

RFC 9293 doesn't distinguish between regular data segments and FIN segments for the purposes of retransmissions. Our existing retransmission logic will also work for FIN segments, except for one detail: we don't currently set the ACK_FROM_TAP_DUE flag when we send a FIN. Add the flag, so that we'll properly retransmit FIN segments like data segments. Remove the section from the theory of operation comment that describes a different way of handling FIN timeouts which (a) isn't correct behaviour and (b) doesn't appear to be implemented. I've tested this by adding logic to suppress sending the FIN if retries < some non-zero value. We correctly resend the FIN and close normally after the expected timeouts. Link: https://bugs.passt.top/show_bug.cgi?id=195 Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- tcp.c | 4 ---- tcp_buf.c | 1 + tcp_vu.c | 1 + 3 files changed, 2 insertions(+), 4 deletions(-) diff --git a/tcp.c b/tcp.c index 17e5b006..dbfde2e0 100644 --- a/tcp.c +++ b/tcp.c @@ -190,10 +190,6 @@ * - RTO_INIT_AFTER_SYN_RETRIES: if SYN retries happened during handshake and * RTO is less than this, re-initialise RTO to this for data retransmissions * - * - FIN_TIMEOUT: if a FIN segment was sent to tap/guest (flag ACK_FROM_TAP_DUE - * with TAP_FIN_SENT event), and no ACK is received within this time, reset - * the connection - * * - FIN_TIMEOUT: if a FIN segment was acknowledged by tap/guest and a FIN * segment (write shutdown) was sent via socket (events SOCK_FIN_SENT and * TAP_FIN_ACKED), but no socket activity is detected from the socket within diff --git a/tcp_buf.c b/tcp_buf.c index 5d419d36..d2925410 100644 --- a/tcp_buf.c +++ b/tcp_buf.c @@ -407,6 +407,7 @@ int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) } conn_event(c, conn, TAP_FIN_SENT); + conn_flag(c, conn, ACK_FROM_TAP_DUE); } return 0; diff --git a/tcp_vu.c b/tcp_vu.c index db9db78a..b9e9b55e 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -425,6 +425,7 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) } conn_event(c, conn, TAP_FIN_SENT); + conn_flag(c, conn, ACK_FROM_TAP_DUE); } return 0; -- 2.52.0

1 0

[PATCH 0/2] Fix errors in FIN timeout logic
by David Gibson 30 Jan '26

30 Jan '26

While investigating bug 179, I found a number of things that confused me about the TCP timer handling. One of them, I think I figured out what's going on and what should be done about it. So, here are the changes. This is mostly about FIN handling and only tangentially about the timer, but it does at least slightly simplify the timer handling while I figure out the rest of it. David Gibson (2): tcp: Retransmit FINs like data segments tcp: Eliminate FIN_TIMEOUT tcp.c | 18 ------------------ tcp_buf.c | 1 + tcp_vu.c | 1 + 3 files changed, 2 insertions(+), 18 deletions(-) -- 2.52.0

2 4

Thoughts on interface modes / multiple guest addresses
by David Gibson 29 Jan '26

29 Jan '26

Hi Jon, As discussed on the call yesterday, I've written up my thoughts on what a bunch of the address semantics should be. Turns out I'd already done some of this at: https://pad.passt.top/p/InterfaceMode I've now updated to cover some more things, and considering the possibility of multiple guest addresses.. Turns out etherpad doesn't really do tables, so it's two sections for the two suggested modes, with matching subheadings. It's still very much a draft so: * It might be unclear - please ask me to clarify anything * It will have some mistakes - make your case if you think my proposed semantics don't make sense * It will be incomplete - feel free to add extra subheadings for anything you -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson

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[PATCH 0/3] Fix bugs with RST propagation
by David Gibson 28 Jan '26

28 Jan '26

In various circumstances we may not properly report abrupt ends to a TCP connection to peers with an RST. Fix them. Link: https://bugs.passt.top/show_bug.cgi?id=191 Link: https://bugs.passt.top/show_bug.cgi?id=193 David Gibson (3): doc: Add test program verifying socket RST behaviour tcp: Properly propagate tap-side RST to socket side tcp_splice: Force TCP RST on abnormal close conditions doc/platform-requirements/.gitignore | 1 + doc/platform-requirements/Makefile | 8 +- doc/platform-requirements/tcp-close-rst.c | 204 ++++++++++++++++++++++ tcp.c | 37 +++- tcp_splice.c | 58 ++++-- 5 files changed, 290 insertions(+), 18 deletions(-) create mode 100644 doc/platform-requirements/tcp-close-rst.c -- 2.52.0

2 5

[PATCH v2 0/9] Introduce multiple addresses
by Jon Maloy 27 Jan '26

27 Jan '26

This version contains what I perceive as the least controversial parts of my previous RFC series. It basically makes address handling behave like before, but now allowing multiple addresses both at the host side and the guest side. v2: - Added the earlier standalone CIDR commit to the head of the series. - Replaced the guest namespace interface subscriptions with just an address observation feature, so that it works with both PASTA and PASST. - Unified 'no_copy_addrs' and 'copy_addrs' code paths, as suggested by David G. - Multiple other changes, also based on feedback from David. - Removed the host interface subscription patches, -for now. I intend to re-add them once this series is applied. - Outstanding question: When do we add an IPv4 link local address to the guest? Only in local/opaque mode? Only when explicitly requested? Always? Jon Maloy (9): conf: Support CIDR notation for -a/--address option ip: Introduce unified multi-address data structures conf: Refactor conf_print() for multi-address support fwd: Check all configured addresses in guest accessibility functions arp: Check all configured addresses in ARP filtering conf: Allow multiple -a/--address options per address family pasta: Unify address configuration paths using address array ip: Track observed guest IPv4 addresses in unified address array ip: Track observed guest IPv6 addresses in unified address array arp.c | 12 ++- conf.c | 290 +++++++++++++++++++++++++++++++++++++----------------- dhcp.c | 8 +- dhcpv6.c | 10 +- dhcpv6.h | 2 +- fwd.c | 137 ++++++++++++++++++++------ inany.c | 29 ++++++ inany.h | 19 ++++ ip.c | 21 ++++ ip.h | 6 ++ migrate.c | 105 ++++++++++++++++++-- ndp.c | 6 +- netlink.c | 84 ++++++++++++++++ netlink.h | 5 + passt.1 | 17 +++- passt.h | 26 ++--- pasta.c | 54 ++++++---- tap.c | 116 ++++++++++++++++++---- 18 files changed, 744 insertions(+), 203 deletions(-) -- 2.52.0

3 28

[PATCH] tcp: Add error checking for flow_epoll_set() in tcp_flow_migrate_target()
by Stefano Brivio 26 Jan '26

26 Jan '26

Commit 90287c2a774e ("tcp: Register fds with epoll at flow creation") added a call to flow_epoll_set() in tcp_flow_migrate_target() without checking for the error code. As Laurent explains, that's harmless, as tcp_flow_migrate_target_ext() will clean up the flow anyway, and we'll just uselessly call flow_hash_insert() before removing it again. But Coverity Scan complains about the unchecked return code, so check it, skip flow_hash_insert() in that case, and explain in comments why we don't have to do anything else. Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com> --- tcp.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/tcp.c b/tcp.c index 6a26826..0a6b7ff 100644 --- a/tcp.c +++ b/tcp.c @@ -3684,17 +3684,19 @@ int tcp_flow_migrate_target(struct ctx *c, int fd) if ((rc = tcp_flow_repair_socket(c, conn))) { flow_err(flow, "Can't set up socket: %s, drop", strerror_(-rc)); - /* Can't leave the flow in an incomplete state */ - FLOW_ACTIVATE(conn); - return 0; + goto out; } flow_epollid_set(&conn->f, EPOLLFD_ID_DEFAULT); - flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->sock, !TAPSIDE(conn)); + if (flow_epoll_set(&conn->f, EPOLL_CTL_ADD, 0, conn->sock, + !TAPSIDE(conn))) + goto out; /* tcp_flow_migrate_target_ext() will clean this up */ flow_hash_insert(c, TAP_SIDX(conn)); - FLOW_ACTIVATE(conn); +out: + /* Never leave the flow in an incomplete state */ + FLOW_ACTIVATE(conn); return 0; } -- 2.43.0

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