Prepare v3.1

.gitignore

@@ -27,3 +27,7 @@ crash-*
 leak-*
 timeout-*
 oom-*
+
+# Test helper
+test/solicit
+test/.deps/

ChangeLog.md

@@ -3,10 +3,60 @@ Change Log
 
 All relevant, user visible, changes are documented in this file.
 
-[UNRELEASED][]
---------------
+[v3.1][] - 2026-10-21
+---------------------
+
+Faster convergence and Multicast Router Discovery.  `mcd` queries the
+LAN as soon as a bridge port starts forwarding, can advertise itself
+to snooping switches that learn router ports from MRD, and follows an
+interface's own `query-interval` in all its timers.  Many fixes for
+robustness, found by fuzzing and static analysis in the Nix flake
+contributed by Dave Seddon.
+
+> **Note:** the router timeout and the group membership interval now
+> follow an interface's own `query-interval`.  With `query-interval 4`
+> on a bridge, `mcd` takes over from a silent querier after 13 sec and
+> drops a group without members after 18 sec, not after 255 and 260
+> sec.  An explicit `router-timeout` still applies to all interfaces.
+
+### Changes
+ - General query when a bridge port starts forwarding, RFC 4541 §2.1.1.
+   Link up, STP settling and a port added to the bridge all count, for
+   the bridge itself and VLAN interfaces on top of it.  Hosts behind
+   the port are back in the MDB within the response interval instead
+   of at the next periodic query.  On by default, see `topology-query`
+   in mcd.conf(5)
+ - Multicast Router Discovery, RFC 4286, IGMP and MLD.  New `iface`
+   keyword `mrd on` advertises `mcd` as a multicast router to the
+   snooping switches on the LAN, answers their solicitations, and sends
+   a termination on the way down.  Off by default.  New global keyword
+   `mrd-interval` sets the advertisement interval, 4 to 180 sec
+ - `mctl show routers` lists the multicast routers heard through MRD
+   on each interface, with their advertised intervals.  `mctl show
+   interfaces` has a new MRD column
+ - `mctl show interfaces json` lists each interface's router timeout
+   as `router-timeout`.  `mctl show` labels the global value as the
+   default
+ - New `mcd -t` option to check a configuration file and exit, like
+   `nginx -t`.  Errors are reported as `FILE:LINE: message`, and it
+   runs as a normal user
+ - Shell completion for `mctl`, bash and zsh.  The commands come from
+   the running daemon, via the new `mctl -C` option.  Installed with
+   `make install`, see `--with-bash-completion-dir` and
+   `--with-zsh-completion-dir`
+ - Nix flake with a development shell, native and cross builds, OCI
+   images, static analysis, fuzzing, and the test suite in microVMs,
+   see `nix/README.md`.  By Dave Seddon
 
 ### Fixes
+ - Fix router timeout (other querier present interval) ignoring the
+   configured `robustness`, query and response intervals.  It was always
+   255 sec unless `router-timeout` was set, it now follows each
+   interface's own `query-interval`
+ - Fix group membership interval ignoring the interface's own
+   `query-interval`
+ - Fix `-l LEVEL` having no effect in the foreground, `mcd -n` printed
+   every message, debug included, whatever the level
  - Fix `mctl show router-ports` and `show igmp json` missing the router
    ports of bridges with a hyphen in their name, e.g. `br-0`
  - Fix shell command injection through bridge names when listing router
@@ -15,9 +65,6 @@ All relevant, user visible, changes are documented in this file.
    the client
  - Fix `mcd` dying of `SIGPIPE` when an IPC client hangs up before
    reading its reply
- - Fix default router timeout (other querier present interval) ignoring
-   the configured `robustness`, query and response intervals, it was
-   always 255 sec unless `router-timeout` was set
  - Fix `mcd` exiting 0 when it cannot fork to daemonize
  - Fix `mctl` crashing on a daemon command of more than 32 words
  - Fix timers stopping if an expiry landed exactly on a whole second
@@ -295,7 +342,8 @@ Initial public release.
 Limited IGMPv1/v2/v3 querier with hard-coded query interval, etc.  Put
 interfaces in a .conf file, whitespace separated to enable querier.
 
-[UNRELEASED]: https://github.com/kernelkit/mcd/compare/v3.0...HEAD
+[UNRELEASED]: https://github.com/kernelkit/mcd/compare/v3.1...HEAD
+[v3.1]:       https://github.com/kernelkit/mcd/compare/v3.0...v3.1
 [v3.0]:       https://github.com/kernelkit/mcd/compare/v2.4...v3.0
 [v2.4]:       https://github.com/kernelkit/mcd/compare/v2.3...v2.4
 [v2.3]:       https://github.com/kernelkit/mcd/compare/v2.2...v2.3

Makefile.am

@@ -1,12 +1,21 @@
 doc_DATA         = README.md ChangeLog.md LICENSE mcd.conf
 EXTRA_DIST       = README.md ChangeLog.md LICENSE mcd.conf doc/overview.svg doc/querier-timeline.svg doc/why.svg
+EXTRA_DIST      += completions/bash/mctl completions/zsh/_mctl
 DISTCLEANFILES   = *~ DEADJOE semantic.cache *.gdb *.elf core core.* *.d
 SUBDIRS          = man src
 
 if ENABLE_TEST
 SUBDIRS         += test
 endif
 
+if BASHCOMP
+bashcomp_DATA    = completions/bash/mctl
+endif
+
+if ZSHCOMP
+zshcomp_DATA     = completions/zsh/_mctl
+endif
+
 ## Check if tagged in git
 release-hook:
 	@if [ "x`git tag -l v$(PACKAGE_VERSION)|grep $(PACKAGE_VERSION)`" = "x" ]; then	\

README.md

@@ -71,6 +71,11 @@ Features
   `robustness` queries spaced `query-interval / 4` apart, per RFC 3376
   §8.6 and §8.7.  A host that missed the first query gets another one
   within half a minute instead of waiting a full query interval.
+- Topology query.  When a bridge port starts forwarding, after link
+  up, STP settling or being added to the bridge, `mcd` sends a general
+  query at once, per RFC 4541 §2.1.1.  Hosts behind the port are back
+  in the MDB within the response interval instead of at the next
+  periodic query, up to two minutes later with the defaults.
 - Version fallback.  Starts at IGMPv3 and MLDv2, drops to the older
   versions when such hosts appear, and returns when they go quiet.
 - Proxy mode, a backup querier that sends from `0.0.0.0` or `::` and can
@@ -79,6 +84,9 @@ Features
 - Raw VLAN mode.  Run a querier directly on a VLAN of a filtering
   bridge, no `vlanN` interface required.
 - Static groups, joined in the kernel so they never time out.
+- Multicast Router Discovery, RFC 4286.  With `mrd on`, `mcd` advertises
+  itself to the snooping switches on the LAN, for the ones that learn
+  their router ports from MRD rather than from queries.
 - `mctl` shows interface and querier status, group memberships, router
   ports per bridge, and the bridge MDB in a readable form.  JSON output
   for scripts, a watch mode for humans.
@@ -202,24 +210,25 @@ arguments for an overview:
     $ mctl
     Multicast Overview
     Query Interval (default): 125 sec
-    Router Timeout          : 255
+    Router Timeout (default): 255 sec
     Fast Leave Ports        :
     Router Ports            : eth3
     Flood Ports             :
 
-    Interface       VID  Proto  Querier                      State  Interval  Timeout  Ver
-    vlan1                IGMP   192.168.1.1                     Up       125     None    3
-    vlan1                MLD    fe80::7a4c:9bff:fe12:3456       Up       125     None    2
-    vlan2                IGMP   192.168.2.1                     Up       125     None    3
-    vlan2                MLD    fe80::7a4c:9bff:fe12:3456       Up       125     None    2
-    br0              42  IGMP   0.0.0.0                         Up       125     None    3
-    br0              42  MLD    ::                              Up       125     None    2
+    Interface       VID  Proto  Querier                      State  Interval  Timeout  MRD  Ver
+    vlan1                IGMP   192.168.1.1                     Up       125     None   on    3
+    vlan1                MLD    fe80::7a4c:9bff:fe12:3456       Up       125     None   on    2
+    vlan2                IGMP   192.168.2.1                     Up       125     None   on    3
+    vlan2                MLD    fe80::7a4c:9bff:fe12:3456       Up       125     None   on    2
+    br0              42  IGMP   0.0.0.0                         Up       125     None  off    3
+    br0              42  MLD    ::                              Up       125     None  off    2
 
     Bridge          VID  Multicast Group       Ports
     br0               2  239.1.1.1             eth3
 
 The parts are also available on their own, as `show interfaces`,
-`show groups`, `show router-ports` and `show mdb`.  Add `json` to any
+`show groups`, `show router-ports` and `show mdb`.  `show routers`
+lists the multicast routers heard through MRD.  Add `json` to any
 `show` command for machine readable output, and `-m` to keep it
 updating like `watch(1)`.  All commands and options are in
 [mctl(8)][].
@@ -243,10 +252,11 @@ it in the foreground with more logging:
     sudo mcd -n -l info
 
 `SIGHUP` reloads the configuration and probes the interfaces again.
-To run several instances, give each its own identity with `-i NAME`,
-which also names its configuration file, PID file and IPC socket, and
-point `mctl -i NAME` at the one you want.  The options, signals and
-files are in [mcd(8)][].
+To check a configuration file before loading it, run `mcd -t -f FILE`
+as any user.  To run several instances, give each its own identity
+with `-i NAME`, which also names its configuration file, PID file and
+IPC socket, and point `mctl -i NAME` at the one you want.  The
+options, signals and files are in [mcd(8)][].
 
 
 Building
@@ -267,6 +277,7 @@ Options worth knowing:
 |------------------------|------------------------------------------------------------|
 | `--with-group=NAME`    | Group owner of `/run/mcd.sock`, default `root`.  Use e.g. `wheel` to let admins run `mctl` without `sudo` |
 | `--enable-test`        | Build the test suite, see [Testing](#testing)              |
+| `--with-bash-completion-dir=DIR`, `--with-zsh-completion-dir=DIR` | Where to install the `mctl` completion scripts, default under `DATADIR`, `no` to skip |
 | `--prefix=`, `--sysconfdir=` | The usual, defaults are `/usr/local` and `/etc`      |
 
 Configure prints a summary at the end, check it before running `make`.

completions/bash/mctl

@@ -0,0 +1,36 @@
+# bash completion for mctl(8)
+#
+# The commands come from the running mcd, via mctl -C, so there is
+# nothing to complete when it is down, apart from the options.
+
+_mctl()
+{
+    local cur=${COMP_WORDS[COMP_CWORD]}
+    local prev=${COMP_WORDS[COMP_CWORD-1]}
+    local word
+
+    case $prev in
+	-u|--ipc)
+	    COMPREPLY=($(compgen -f -- "$cur"))
+	    return
+	    ;;
+	-i|--ident)
+	    return
+	    ;;
+    esac
+
+    if [[ $cur == -* ]]; then
+	COMPREPLY=($(compgen -W '-h --help -i --ident -m --monitor -p --plain
+				 -t --no-heading -u --ipc -v --version' -- "$cur"))
+	return
+    fi
+
+    # All words so far, options included, so -i NAME and -u FILE reach
+    # the same daemon the command will.  The last word is the partial.
+    COMPREPLY=()
+    while IFS=$'\t' read -r word _; do
+	COMPREPLY+=("$word")
+    done < <(mctl -C "${COMP_WORDS[@]:1:COMP_CWORD}" 2>/dev/null)
+}
+
+complete -F _mctl mctl

completions/zsh/_mctl

@@ -0,0 +1,34 @@
+#compdef mctl
+#
+# zsh completion for mctl(8).  The commands come from the running
+# mcd, via mctl -C, with their descriptions.
+
+_mctl() {
+    # The line as typed, _arguments rewrites $words for the command
+    local -a typed=("${words[@]}") cands
+    local cur=$CURRENT line
+
+    _arguments -s \
+	'(-h --help)'{-h,--help}'[Show usage and the available commands]' \
+	'(-i --ident)'{-i,--ident}'[Talk to the mcd started with this identity]:name' \
+	'(-m --monitor)'{-m,--monitor}'[Run the command every two seconds]' \
+	'(-p --plain)'{-p,--plain}'[Plain table headings]' \
+	'(-t --no-heading)'{-t,--no-heading}'[Skip table headings]' \
+	'(-u --ipc)'{-u,--ipc}'[IPC socket]:file:_files' \
+	'(-v --version)'{-v,--version}'[Show version and exit]' \
+	'*::command:->command' && return
+
+    case $state in
+	command)
+	    # All words so far, options included, so -i NAME and -u FILE
+	    # reach the same daemon the command will.  word<TAB>desc
+	    # becomes word:desc for _describe
+	    for line in ${(f)"$(mctl -C "${typed[@]:1:cur-1}" 2>/dev/null)"}; do
+		cands+=("${line/$'\t'/:}")
+	    done
+	    _describe -t commands 'mctl command' cands
+	    ;;
+    esac
+}
+
+_mctl "$@"

configure.ac

@@ -1,5 +1,5 @@
 AC_PREREQ([2.69])
-AC_INIT([mcd], [3.0], [https://github.com/kernelkit/mcd/issues])
+AC_INIT([mcd], [3.1], [https://github.com/kernelkit/mcd/issues])
 AC_CONFIG_AUX_DIR(.aux)
 AM_INIT_AUTOMAKE([1.11 foreign])
 AM_SILENT_RULES([yes])
@@ -65,6 +65,19 @@ AC_ARG_WITH(group,
 	AS_HELP_STRING([--with-group=NAME], [Group for /run/mcd.sock (mctl), default: root]),
 	[group=$withval], [group=root])
 
+AC_ARG_WITH(bash-completion-dir,
+	AS_HELP_STRING([--with-bash-completion-dir=DIR], [Install mctl bash completion in DIR, default: DATADIR/bash-completion/completions, no to skip]),
+	[bashcompdir=$withval], [bashcompdir=yes])
+
+AC_ARG_WITH(zsh-completion-dir,
+	AS_HELP_STRING([--with-zsh-completion-dir=DIR], [Install mctl zsh completion in DIR, default: DATADIR/zsh/site-functions, no to skip]),
+	[zshcompdir=$withval], [zshcompdir=yes])
+
+AS_IF([test "x$bashcompdir" = "xyes"], [bashcompdir='$(datadir)/bash-completion/completions'])
+AS_IF([test "x$zshcompdir" = "xyes"], [zshcompdir='$(datadir)/zsh/site-functions'])
+AC_SUBST(bashcompdir)
+AC_SUBST(zshcompdir)
+
 # Create config.h from selected features and fallback defautls
 AS_IF([test "x$with_group" != "xno"], [
 	AS_IF([test "x$group" = "xyes"], [
@@ -74,6 +87,8 @@ AC_DEFINE_UNQUOTED(DEFGROUP, "$group", [For /run/finit/socket])
 AM_CONDITIONAL(BSD,         [test "x$ac_cv_header_net_if_dl_h"     = "xyes"])
 AM_CONDITIONAL(LINUX,       [test "x$ac_cv_header_linux_netlink_h" = "xyes"])
 AM_CONDITIONAL(ENABLE_TEST, [test "x$enable_test"                 != "xno"])
+AM_CONDITIONAL(BASHCOMP,    [test "x$bashcompdir"                 != "xno"])
+AM_CONDITIONAL(ZSHCOMP,     [test "x$zshcompdir"                  != "xno"])
 
 # Workaround for as-of-yet unreleased runstatedir support, planned for
 # autoconf 2.70, which some major distros have backported.
@@ -95,6 +110,8 @@ cat <<EOF
 Optional features:
   IPC group.............: $group
   Unit tests............: $enable_test
+  Bash completion.......: $bashcompdir
+  Zsh completion........: $zshcompdir
 
 ------------- Compiler version --------------
 $($CC --version || true)

man/mcd.8

@@ -1,13 +1,13 @@
 .\"  -*- nroff -*-
-.Dd October 16, 2026
+.Dd October 21, 2026
 .Dt MCD 8 SMM
 .Os
 .Sh NAME
 .Nm mcd
 .Nd IGMP and MLD querier for the Linux bridge
 .Sh SYNOPSIS
 .Nm
-.Op Fl hnsv
+.Op Fl hnstv
 .Op Fl f Ar FILE
 .Op Fl i Ar NAME
 .Op Fl l Ar LEVEL
@@ -48,6 +48,13 @@ queries,
 .Cm query-interval
 / 4 apart, RFC 3376 \(sc8.6 and \(sc8.7.
 .It
+General query when a port of the bridge starts forwarding, so hosts
+behind it are back in the MDB within the response interval, not at the
+next query interval, RFC 4541 \(sc2.1.1.  See
+.Cm topology-query
+in
+.Xr mcd.conf 5 .
+.It
 Starts at IGMPv3 and MLDv2 and falls back to IGMPv2, IGMPv1 or MLDv1
 for as long as older hosts are heard.
 .It
@@ -59,6 +66,13 @@ VLAN interface on top.
 .It
 Static groups, joined in the kernel so the bridge always forwards them
 to itself.
+.It
+Multicast Router Discovery, RFC 4286, for switches that learn their
+router ports from MRD advertisements rather than from queries.  Off by
+default, see
+.Cm mrd
+in
+.Xr mcd.conf 5 .
 .El
 .Pp
 Interfaces, links and addresses are followed with netlink, so an
@@ -101,6 +115,11 @@ a reload completes.
 Log to syslog, the default unless
 .Fl n
 is given.
+.It Fl t , -check-config
+Check the configuration file and exit without starting the daemon.
+Errors are reported as
+.Ar FILE:LINE: message
+with a non-zero exit status.  Runs as a normal user.
 .It Fl u , -ipc Ns = Ns Ar FILE
 IPC socket used by
 .Xr mctl 8 ,