core: add NMBondManager to handle NTF rules for balance-slb (MLAG)

4 files changed, 1002 insertions, 0 deletions

diff --git a/Makefile.am b/Makefile.am
index 6b9b82876b..13cadec6dc 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -2462,6 +2462,8 @@ src_core_libNetworkManagerBase_la_SOURCES = \
 	src/core/nm-l3cfg.h \
 	src/core/nm-ip-config.c \
 	src/core/nm-ip-config.h \
+	src/core/nm-bond-manager.c \
+	src/core/nm-bond-manager.h \
 	\
 	src/core/dhcp/nm-dhcp-client.c \
 	src/core/dhcp/nm-dhcp-client.h \
diff --git a/src/core/meson.build b/src/core/meson.build
index f3359ad0f5..6f11595aa0 100644
--- a/src/core/meson.build
+++ b/src/core/meson.build
@@ -53,6 +53,7 @@ libNetworkManagerBase = static_library(
     'nm-l3-ipv4ll.c',
     'nm-l3-ipv6ll.c',
     'nm-l3cfg.c',
+    'nm-bond-manager.c',
     'nm-ip-config.c',
   ),
   dependencies: [
diff --git a/src/core/nm-bond-manager.c b/src/core/nm-bond-manager.c
new file mode 100644
index 0000000000..2d15b0b5a0
--- /dev/null
+++ b/src/core/nm-bond-manager.c
@@ -0,0 +1,967 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "src/core/nm-default-daemon.h"
+
+#include "nm-bond-manager.h"
+
+#include <linux/if.h>
+
+#include "NetworkManagerUtils.h"
+#include "libnm-core-aux-intern/nm-libnm-core-utils.h"
+#include "libnm-glib-aux/nm-str-buf.h"
+#include "libnm-platform/nm-platform.h"
+#include "libnm-platform/nmp-object.h"
+#include "nm-firewall-utils.h"
+
+/*****************************************************************************/
+
+typedef enum _nm_packed {
+    REGISTRATION_STATE_NONE,
+    REGISTRATION_STATE_UPPING,
+    REGISTRATION_STATE_UP,
+    REGISTRATION_STATE_DOWNING,
+} RegistrationState;
+
+struct _NMBondManager {
+    NMPlatform *platform;
+
+    NMBondManagerCallback callback;
+    gpointer              user_data;
+
+    /* This is only used for structured logging. */
+    char *connection_uuid;
+
+    GSource *reconfigure_on_idle_source;
+
+    /* During _reconfigure_check() we remember all ifindexes that are part
+     * of the current SLB bond. This is used during _link_changed_cb() to
+     * figure out whether a change on the interface might be relevant to
+     * trigger a _reconfigure_check() on idle. */
+    GHashTable *previous_ifindexes;
+
+    /* We need to keep track of active members that we configured in NFT.
+     * That is, because on update we use "add && flush" to reset the table,
+     * however that leaves empty chains around. If we previously had an active
+     * member, a chain for it was created that we need to clean up.
+     *
+     * Before every NFT call we use this to generate the list of members that
+     * are to be cleaned up. Thereby also adding the new active-memebers to
+     * the list. When the NFT calls returns with success, we can prune the
+     * now deleted member/chain. */
+    GHashTable *previous_members;
+
+    GCancellable *cancellable;
+
+    struct {
+        char        *bond_ifname_curr;
+        char        *bond_ifname_next;
+        const char **active_members_curr;
+        const char **active_members_next;
+    } dat;
+
+    gulong            link_changed_id;
+    int               ifindex;
+    RegistrationState reg_state;
+    bool              destroyed : 1;
+
+    /* Whether we noticed some changes that require us to _reconfigure_check().
+     * Note that while a NFT call is pending, we postpone the check. */
+    bool reconfigure_check : 1;
+
+    /* Whether a `nft` call is in progress. Usually this corresponds to
+     * having a cancellable, however, we may also cancel and clear the
+     * cancellable while the call is still in progress. */
+    bool nft_in_progress : 1;
+
+    /* Whether the last NFT invocation was good. If not, we may have
+     * an invalid state. Actually unused, so far because it's not
+     * clear what to do about failure to configure NFT (aside logging
+     * a warning). */
+    bool nft_good : 1;
+
+    /* The overall state. DEFAULT means that an update is pending.
+     * FALSE means that the last "nft" command failed.
+     * TRUE means that the last "nft" command was good. */
+    NMOptionBool state : 3;
+};
+
+#define NM_IS_BOND_MANAGER(self)                    \
+    ({                                              \
+        const NMBondManager *_self = (self);        \
+                                                    \
+        (_self && NM_IS_PLATFORM(_self->platform)); \
+    })
+
+/*****************************************************************************/
+
+static void _nft_call(NMBondManager     *self,
+                      gboolean           up,
+                      const char        *bond_ifname,
+                      const char *const *bond_ifnames_down,
+                      const char *const *active_members);
+
+static void _bond_manager_destroy(NMBondManager *self);
+
+static void _reconfigure_check(NMBondManager *self, gboolean reapply);
+
+/*****************************************************************************/
+
+#define _NMLOG_DOMAIN      LOGD_DEVICE
+#define _NMLOG_PREFIX_NAME "mlag"
+#define _NMLOG(level, ...)                                                                           \
+    G_STMT_START                                                                                     \
+    {                                                                                                \
+        const NMLogLevel _level = (level);                                                           \
+                                                                                                     \
+        if (nm_logging_enabled(_level, _NMLOG_DOMAIN)) {                                             \
+            NMBondManager *const _self = (self);                                                     \
+            const char *_ifname        = nm_platform_link_get_name(_self->platform, _self->ifindex); \
+            char        _sbuf[30];                                                                   \
+                                                                                                     \
+            _nm_log(_level,                                                                          \
+                    _NMLOG_DOMAIN,                                                                   \
+                    0,                                                                               \
+                    _ifname,                                                                         \
+                    _self->connection_uuid,                                                          \
+                    "%s[" NM_HASH_OBFUSCATE_PTR_FMT ", %s]: " _NM_UTILS_MACRO_FIRST(__VA_ARGS__),    \
+                    _NMLOG_PREFIX_NAME,                                                              \
+                    NM_HASH_OBFUSCATE_PTR(_self),                                                    \
+                    (_ifname ?: nm_sprintf_buf(_sbuf, "(%d)", _self->ifindex))                       \
+                        _NM_UTILS_MACRO_REST(__VA_ARGS__));                                          \
+        }                                                                                            \
+    }                                                                                                \
+    G_STMT_END
+
+static const char *
+_log_info(NMStrBuf          *strbuf,
+          const char        *bond_ifname,
+          const char *const *active_members,
+          const char *const *previous_members)
+{
+    gsize i;
+
+    nm_str_buf_reset(strbuf);
+
+    if (!bond_ifname)
+        nm_str_buf_append(strbuf, "(disabled)");
+    else {
+        nm_str_buf_append_printf(strbuf, "(enabled, \"%s\"", bond_ifname);
+
+        for (i = 0; active_members && active_members[i]; i++) {
+            if (i == 0)
+                nm_str_buf_append(strbuf, ", active-members=[ \"");
+            else
+                nm_str_buf_append(strbuf, "\", \"");
+            nm_str_buf_append(strbuf, active_members[i]);
+        }
+        if (i > 0)
+            nm_str_buf_append(strbuf, "\" ]");
+
+        for (i = 0; previous_members && previous_members[i]; i++) {
+            nm_assert(!nm_strv_contains(active_members, -1, previous_members[i]));
+            if (i == 0)
+                nm_str_buf_append(strbuf, ", previous-members=[ \"");
+            else
+                nm_str_buf_append(strbuf, "\", \"");
+            nm_str_buf_append(strbuf, previous_members[i]);
+        }
+        if (i > 0)
+            nm_str_buf_append(strbuf, "\" ]");
+
+        nm_str_buf_append(strbuf, ")");
+    }
+
+    return nm_str_buf_get_str(strbuf);
+}
+
+/*****************************************************************************/
+
+static gboolean
+_nm_assert_self_(NMBondManager *self)
+{
+    nm_assert(self);
+    nm_assert(NM_IS_PLATFORM(self->platform));
+    nm_assert(!self->cancellable || G_IS_CANCELLABLE(self->cancellable));
+    nm_assert(!self->cancellable || !g_cancellable_is_cancelled(self->cancellable));
+    nm_assert(!self->dat.active_members_curr || self->dat.bond_ifname_curr);
+    nm_assert(!self->dat.active_members_next || self->dat.bond_ifname_next);
+    nm_assert(!self->cancellable || self->nft_in_progress);
+    nm_assert(!self->reconfigure_on_idle_source || self->reconfigure_check);
+    nm_assert(!self->nft_in_progress || !self->reconfigure_on_idle_source);
+
+    nm_assert(!self->dat.active_members_curr || self->dat.bond_ifname_curr[0]);
+    nm_assert(!self->dat.active_members_next || self->dat.bond_ifname_next[0]);
+
+    nm_assert(!self->destroyed || !self->dat.bond_ifname_next);
+    nm_assert(!self->destroyed
+              || NM_IN_SET((RegistrationState) self->reg_state,
+                           REGISTRATION_STATE_UPPING,
+                           REGISTRATION_STATE_DOWNING));
+
+    switch (self->reg_state) {
+    case REGISTRATION_STATE_NONE:
+        nm_assert(!self->nft_in_progress);
+        nm_assert(!self->cancellable);
+        nm_assert(!self->dat.bond_ifname_curr);
+        nm_assert(!self->dat.bond_ifname_next);
+        break;
+    case REGISTRATION_STATE_UPPING:
+        nm_assert(self->nft_in_progress);
+        nm_assert(self->dat.bond_ifname_curr);
+        break;
+    case REGISTRATION_STATE_UP:
+        nm_assert(!self->nft_in_progress);
+        nm_assert(!self->cancellable);
+        nm_assert(self->dat.bond_ifname_curr);
+        nm_assert(!self->dat.bond_ifname_next);
+        break;
+    case REGISTRATION_STATE_DOWNING:
+        nm_assert(self->nft_in_progress);
+        nm_assert(self->dat.bond_ifname_curr);
+        break;
+    default:
+        nm_assert_not_reached();
+        break;
+    }
+
+    return TRUE;
+}
+
+#define _nm_assert_self(self) nm_assert(_nm_assert_self_(self))
+
+/*****************************************************************************/
+
+static void
+_callback_invoke(NMBondManager *self, NMBondManagerEventType event_type)
+{
+    if (!self->callback)
+        return;
+
+    self->callback(self, event_type, self->user_data);
+}
+
+static void
+_notify_state_change(NMBondManager *self)
+{
+    NMOptionBool state;
+
+    if (self->nft_in_progress)
+        state = NM_OPTION_BOOL_DEFAULT;
+    else
+        state = !!self->nft_good;
+
+    if (state == self->state)
+        return;
+
+    self->state = state;
+    _callback_invoke(self, NM_BOND_MANAGER_EVENT_TYPE_STATE);
+}
+
+/*****************************************************************************/
+
+static void
+_nft_call_cb(GObject *source, GAsyncResult *result, gpointer user_data)
+{
+    nm_auto_str_buf NMStrBuf strbuf = NM_STR_BUF_INIT_A(NM_UTILS_GET_NEXT_REALLOC_SIZE_232, FALSE);
+    NMBondManager           *self;
+    gpointer                 ptr_up;
+    gs_free const char     **previous_members = NULL;
+    gs_free_error GError    *error            = NULL;
+
+    nm_utils_user_data_unpack(user_data, &self, &ptr_up, &previous_members);
+
+    _nm_assert_self(self);
+
+    self->nft_in_progress = FALSE;
+
+    nm_firewall_nft_call_finish(result, &error);
+
+    if (!error) {
+        gsize i;
+
+        /* On success, we can forget about our previous members that we successfully
+         * deleted. */
+        if (!GPOINTER_TO_INT(ptr_up)) {
+            /* We successfully deleted the NFT table. Forget all previous members. */
+            g_hash_table_remove_all(self->previous_members);
+        } else if (previous_members) {
+            /* These previous members are now forgotten for good. */
+            for (i = 0; previous_members[i]; i++)
+                g_hash_table_remove(self->previous_members, previous_members[i]);
+        }
+    } else {
+        /* If all our NFT calls keep failing, we never actually prune entries from
+         * self->previous_members. That is a problem, however, under normal operation
+         * NFT calls should not continuously fail, and we would have a small fixed
+         * number of active-members. */
+    }
+
+    nm_clear_g_cancellable(&self->cancellable);
+
+    if (nm_utils_error_is_cancelled(error)) {
+        switch (self->reg_state) {
+        case REGISTRATION_STATE_NONE:
+        case REGISTRATION_STATE_UP:
+        case REGISTRATION_STATE_DOWNING:
+            /* It is not expected that we cancel anything in this state. */
+            nm_assert_not_reached();
+            goto out;
+        case REGISTRATION_STATE_UPPING:
+            nm_assert(self->dat.bond_ifname_curr);
+            /* We cancelled while upping. We need to issue another down,
+             * to make sure the data is gone. */
+            if (!self->dat.bond_ifname_next) {
+                /* There is no other name to configure. We just need to down
+                 * the current one. */
+                _LOGT("reconfigure: configuration cancelled, deconfigure %s",
+                      self->dat.bond_ifname_curr);
+                _nft_call(self, FALSE, self->dat.bond_ifname_curr, NULL, NULL);
+                self->reg_state = REGISTRATION_STATE_DOWNING;
+                goto out;
+            }
+            /* There is already another configuration. UPPING again. */
+            _LOGT("reconfigure: configuration cancelled, configure %s",
+                  _log_info(&strbuf,
+                            self->dat.bond_ifname_next,
+                            self->dat.active_members_next,
+                            NULL));
+            _nft_call(self,
+                      TRUE,
+                      self->dat.bond_ifname_next,
+                      NM_MAKE_STRV(self->dat.bond_ifname_curr),
+                      self->dat.active_members_next);
+            self->reg_state = REGISTRATION_STATE_UPPING;
+            nm_clear_g_free(&self->dat.bond_ifname_curr);
+            nm_clear_g_free(&self->dat.active_members_curr);
+            self->dat.bond_ifname_curr    = g_steal_pointer(&self->dat.bond_ifname_next);
+            self->dat.active_members_curr = g_steal_pointer(&self->dat.active_members_next);
+            goto out;
+        }
+        nm_assert_not_reached();
+        goto out;
+    }
+
+    if (error) {
+        self->nft_good = FALSE;
+    } else {
+        /* Technically, if a previous downing failed, we cannot know that
+         * we were able to fix this bug a successful run now. That is, because
+         * if the interface got renamed, and the downing for the previous
+         * interface name failed, we leak that table and the success now doesn't
+         * fix that.
+         *
+         * That is a bug, but probably not severe because:
+         * - interfaces are not supposed to be renamed.
+         * - if this NFT command succeed, we expect that also the previous downings worked.
+         *
+         * The problem here is only that nft_good might lie and indicate
+         * no problem. However, when a downing fails, we anyway leak the table already
+         * and the bad thing happend. We cannot fix if `nft` command fails.
+         */
+        self->nft_good = TRUE;
+    }
+
+    switch (self->reg_state) {
+    case REGISTRATION_STATE_NONE:
+    case REGISTRATION_STATE_UP:
+        /* Unexpected to get a callback completion in these states. */
+        nm_assert_not_reached();
+        goto out;
+    case REGISTRATION_STATE_UPPING:
+        nm_assert(!self->dat.bond_ifname_next);
+        if (error) {
+            /* Unclear what to do about this error. Just log about it, nothing else. */
+            _LOGW("reconfigure: nft configuration for balance-slb failed: %s", error->message);
+        } else
+            _LOGT("reconfigure: configuration completed");
+        self->reg_state = REGISTRATION_STATE_UP;
+        goto out;
+    case REGISTRATION_STATE_DOWNING:
+        nm_assert(self->dat.bond_ifname_curr);
+        if (!self->dat.bond_ifname_next) {
+            if (error) {
+                /* Unclear what to do about this error. Just log about it, nothing else. */
+                _LOGW("reconfigure: nft deconfiguration for balance-slb failed: %s",
+                      error->message);
+            } else
+                _LOGT("reconfigure: deconfiguration completed");
+            nm_clear_g_free(&self->dat.bond_ifname_curr);
+            nm_clear_g_free(&self->dat.active_members_curr);
+            self->reg_state = REGISTRATION_STATE_NONE;
+
+            if (self->destroyed) {
+                _bond_manager_destroy(self);
+                return;
+            }
+
+            goto out;
+        }
+        if (error) {
+            /* Unclear what to do about this error. Just log about it, nothing else. */
+            _LOGW("reconfigure: nft deconfiguration failed before restart: %s", error->message);
+        } else
+            _LOGT("reconfigure: deconfiguration completed before restart");
+        _nft_call(self,
+                  TRUE,
+                  self->dat.bond_ifname_next,
+                  NM_MAKE_STRV(self->dat.bond_ifname_curr),
+                  self->dat.active_members_next);
+        nm_clear_g_free(&self->dat.bond_ifname_curr);
+        nm_clear_g_free(&self->dat.active_members_curr);
+        self->dat.bond_ifname_curr    = g_steal_pointer(&self->dat.bond_ifname_next);
+        self->dat.active_members_curr = g_steal_pointer(&self->dat.active_members_next);
+        self->reg_state               = REGISTRATION_STATE_UPPING;
+        goto out;
+    }
+
+    nm_assert_not_reached();
+
+out:
+    if (self->reconfigure_check) {
+        if (self->destroyed)
+            nm_assert_not_reached();
+        else if (!self->nft_in_progress) {
+            nm_assert(!self->reconfigure_on_idle_source);
+            _reconfigure_check(self, FALSE);
+        }
+    }
+
+    _notify_state_change(self);
+}
+
+static void
+_nft_call(NMBondManager     *self,
+          gboolean           up,
+          const char        *bond_ifname,
+          const char *const *bond_ifnames_down,
+          const char *const *active_members)
+{
+    gs_unref_bytes GBytes     *stdin_buf             = NULL;
+    gs_free const char *const *previous_members_strv = NULL;
+
+    if (up) {
+        gs_unref_ptrarray GPtrArray *arr = NULL;
+        GHashTableIter               iter;
+        const char                  *n;
+        gsize                        i;
+
+        /* We need to track the active-members that we add, because, when we update the
+         * NFT table without the member from previously, we use "add && flush", which
+         * leaves empty chains for the previous members around. We need to cleanup those
+         * chains, hence the need to track which members we ever added.
+         *
+         * Before making an UP call, we add the newly configured active_members to the list
+         * of previous_members. All the while, passing a list of previous_members_strv
+         * which we currently no longer configure.
+         *
+         * Only when the call succeeds (in _nft_call_cb()), we will forget about previously added
+         * members. This is done by passing the list of members that we are forgetting now
+         * on to the callback below. */
+
+        /* Get the list of previous members that are no longer in the current
+         * active list. */
+        g_hash_table_iter_init(&iter, self->previous_members);
+        while (g_hash_table_iter_next(&iter, (gpointer *) &n, NULL)) {
+            if (nm_strv_contains(active_members, -1, n))
+                continue;
+            if (!arr)
+                arr = g_ptr_array_new();
+            g_ptr_array_add(arr, (gpointer) n);
+        }
+        if (arr) {
+            nm_strv_sort((const char **) arr->pdata, arr->len);
+            previous_members_strv = nm_strv_dup_packed((const char *const *) arr->pdata, arr->len);
+        }
+
+        /* The now active member also get tracked as previous members for the future. */
+        if (active_members) {
+            for (i = 0; active_members[i]; i++)
+                g_hash_table_add(self->previous_members, g_strdup(active_members[i]));
+        }
+    }
+
+    stdin_buf = nm_firewall_nft_stdio_mlag(up,
+                                           bond_ifname,
+                                           bond_ifnames_down,
+                                           active_members,
+                                           previous_members_strv);
+
+    nm_clear_g_cancellable(&self->cancellable);
+    self->cancellable = g_cancellable_new();
+
+    nm_shutdown_wait_obj_register_cancellable(self->cancellable, "nft-mlag");
+
+    if (_LOGT_ENABLED()) {
+        if (up) {
+            nm_auto_str_buf NMStrBuf strbuf =
+                NM_STR_BUF_INIT_A(NM_UTILS_GET_NEXT_REALLOC_SIZE_232, FALSE);
+
+            _LOGT("reconfigure: call nft: %s",
+                  _log_info(&strbuf, bond_ifname, active_members, previous_members_strv));
+        } else
+            _LOGT("reconfigure: call nft: disable on \"%s\"", bond_ifname);
+    }
+
+    self->nft_in_progress = TRUE;
+
+    if (self->reconfigure_check)
+        nm_clear_g_source_inst(&self->reconfigure_on_idle_source);
+
+    nm_firewall_nft_call(stdin_buf,
+                         self->cancellable,
+                         _nft_call_cb,
+                         nm_utils_user_data_pack(self,
+                                                 GINT_TO_POINTER(up),
+                                                 g_steal_pointer(&previous_members_strv)));
+}
+
+/*****************************************************************************/
+
+static void
+_reconfigure_do(NMBondManager *self,
+                gboolean       reapply,
+                const char    *bond_ifname,
+                const char   **active_members_take)
+{
+    nm_auto_str_buf NMStrBuf strbuf = NM_STR_BUF_INIT_A(NM_UTILS_GET_NEXT_REALLOC_SIZE_232, FALSE);
+    gs_free const char     **active_members = g_steal_pointer(&active_members_take);
+
+    _nm_assert_self(self);
+    nm_assert(!active_members || bond_ifname);
+    nm_assert(!active_members || active_members[0]);
+
+    /* The difficulty of all of this is "state". In particular, since we make the nft call
+     * async, we need to handle all the possible cases, how an update event can invalidate
+     * a currently pending call. */
+
+    switch (self->reg_state) {
+    case REGISTRATION_STATE_NONE:
+        nm_assert(!self->dat.bond_ifname_curr);
+        nm_assert(!self->dat.active_members_curr);
+        nm_assert(!self->dat.bond_ifname_next);
+        nm_assert(!self->dat.active_members_next);
+        nm_assert(!self->cancellable);
+        nm_assert(!self->nft_in_progress);
+
+        if (!bond_ifname) {
+            /* No configuration done. Nothing to do. */
+            goto out;
+        }
+
+        _LOGT("reconfigure: start configuring (%s)",
+              _log_info(&strbuf, bond_ifname, active_members, NULL));
+        self->dat.bond_ifname_curr    = g_strdup(bond_ifname);
+        self->dat.active_members_curr = nm_strv_dup_packed(active_members, -1);
+        _nft_call(self, TRUE, self->dat.bond_ifname_curr, NULL, self->dat.active_members_curr);
+        self->reg_state = REGISTRATION_STATE_UPPING;
+        goto out;
+    case REGISTRATION_STATE_UPPING:
+        nm_assert(self->dat.bond_ifname_curr);
+        nm_assert(self->nft_in_progress);
+
+        /* We are UPPING, we cancel the pending operation and will
+         * handle the rest when the callback completes. */
+        if (!bond_ifname) {
+            if (self->cancellable || self->dat.bond_ifname_next)
+                _LOGT("reconfigure: aborting configuring");
+            nm_clear_g_free(&self->dat.bond_ifname_next);
+            nm_clear_g_free(&self->dat.active_members_next);
+            nm_clear_g_cancellable(&self->cancellable);
+            goto out;
+        }
+        if (!reapply && self->cancellable && nm_streq0(bond_ifname, self->dat.bond_ifname_curr)
+            && nm_strv_equal(active_members, self->dat.active_members_curr)) {
+            /* Nothing to do. We are already upping this setup. */
+            nm_assert(!self->dat.bond_ifname_next);
+            nm_assert(!self->dat.active_members_next);
+            goto out;
+        }
+        if (!reapply && !self->cancellable && nm_streq0(bond_ifname, self->dat.bond_ifname_next)
+            && nm_strv_equal(active_members, self->dat.active_members_next)) {
+            /* We already cancelled the current upping, and have scheduled another
+             * (identical) run. Nothing to do. */
+            goto out;
+        }
+        _LOGT("reconfigure: abort configuring to configure %s",
+              _log_info(&strbuf, bond_ifname, active_members, NULL));
+        nm_clear_g_free(&self->dat.bond_ifname_next);
+        nm_clear_g_free(&self->dat.active_members_next);
+        self->dat.bond_ifname_next    = g_strdup(bond_ifname);
+        self->dat.active_members_next = nm_strv_dup_packed(active_members, -1);
+        nm_clear_g_cancellable(&self->cancellable);
+        goto out;
+    case REGISTRATION_STATE_UP:
+        nm_assert(self->dat.bond_ifname_curr);
+        nm_assert(!self->dat.bond_ifname_next);
+        nm_assert(!self->dat.active_members_next);
+        nm_assert(!self->cancellable);
+        nm_assert(!self->nft_in_progress);
+
+        if (!bond_ifname) {
+            _LOGT("reconfigure: deconfigure to disable");
+            _nft_call(self, FALSE, self->dat.bond_ifname_curr, NULL, NULL);
+            self->reg_state = REGISTRATION_STATE_DOWNING;
+            goto out;
+        }
+        if (!reapply && nm_streq0(bond_ifname, self->dat.bond_ifname_curr)
+            && nm_strv_equal(active_members, self->dat.active_members_curr)) {
+            /* Nothing to do. The current configuration is already active. */
+            goto out;
+        }
+        _LOGT("reconfigure: configure, update to %s",
+              _log_info(&strbuf, bond_ifname, active_members, NULL));
+        _nft_call(self,
+                  TRUE,
+                  bond_ifname,
+                  NM_MAKE_STRV(self->dat.bond_ifname_curr),
+                  active_members);
+        self->reg_state = REGISTRATION_STATE_UPPING;
+        nm_clear_g_free(&self->dat.bond_ifname_curr);
+        nm_clear_g_free(&self->dat.active_members_curr);
+        self->dat.bond_ifname_curr    = g_strdup(bond_ifname);
+        self->dat.active_members_curr = nm_strv_dup_packed(active_members, -1);
+        goto out;
+    case REGISTRATION_STATE_DOWNING:
+        nm_assert(self->dat.bond_ifname_curr);
+        nm_assert(self->nft_in_progress);
+
+        /* we are already DOWNING. It suffices to clear the scheduled "next"
+         * config and wait, and reset the "next" configuration. */
+        if (nm_streq0(bond_ifname, self->dat.bond_ifname_next)
+            && nm_strv_equal(active_members, self->dat.active_members_next)) {
+            /* Nothing to do. */
+            goto out;
+        }
+        _LOGT("reconfigure: deconfiguring and waiting for %s",
+              _log_info(&strbuf, bond_ifname, active_members, NULL));
+        nm_clear_g_free(&self->dat.bond_ifname_next);
+        nm_clear_g_free(&self->dat.active_members_next);
+        if (bond_ifname) {
+            self->dat.bond_ifname_next    = g_strdup(bond_ifname);
+            self->dat.active_members_next = nm_strv_dup_packed(active_members, -1);
+        }
+        goto out;
+    }
+    nm_assert_not_reached();
+
+out:
+    _notify_state_change(self);
+}
+
+static void
+_reconfigure_check(NMBondManager *self, gboolean reapply)
+{
+    const NMPlatformLink        *plink_ctrl;
+    const NMPlatformLink        *plink_port;
+    const NMPlatformLnkBond     *plnkbond_ctrl;
+    NMDedupMultiIter             pliter;
+    const NMDedupMultiHeadEntry *pl_links_head_entry;
+    const char                  *active_members_lst_stack[16];
+    gs_free const char         **active_members_lst_heap = NULL;
+    const char                 **active_members_lst      = active_members_lst_stack;
+    gsize                        active_members_alloc    = G_N_ELEMENTS(active_members_lst_stack);
+    gsize                        active_members_n        = 0;
+    gs_free const char         **active_members_result   = NULL;
+    const char                  *bond_ifname             = NULL;
+
+    _nm_assert_self(self);
+    nm_assert(!self->destroyed);
+
+    self->reconfigure_check = FALSE;
+    nm_clear_g_source_inst(&self->reconfigure_on_idle_source);
+
+    g_hash_table_remove_all(self->previous_ifindexes);
+
+    plnkbond_ctrl = nm_platform_link_get_lnk_bond(self->platform, self->ifindex, &plink_ctrl);
+
+    /* We only do bonding-slb MLAG handling if our ifindex is a bond with
+     * mode=balance-xor && xmit_hash_policy=vlan+srcmac. */
+    if (!plnkbond_ctrl)
+        goto out;
+    if (!plink_ctrl)
+        goto out;
+    if (plink_ctrl->type != NM_LINK_TYPE_BOND)
+        goto out;
+    if (plnkbond_ctrl->mode != NM_BOND_MODE_XOR)
+        goto out;
+    if (plnkbond_ctrl->xmit_hash_policy != NM_BOND_XMIT_HASH_POLICY_VLAN_SRCMAC)
+        goto out;
+
+    /* Find all the connected ports that are IFF_RUNNING. */
+    pl_links_head_entry = nm_platform_lookup_obj_type(self->platform, NMP_OBJECT_TYPE_LINK);
+    nmp_cache_iter_for_each_link (&pliter, pl_links_head_entry, &plink_port) {
+        if (plink_port->master != self->ifindex)
+            continue;
+        if (!NM_FLAGS_HAS(plink_port->n_ifi_flags, IFF_RUNNING))
+            continue;
+
+        g_hash_table_add(self->previous_ifindexes, GINT_TO_POINTER(plink_port->ifindex));
+
+        if (active_members_n == active_members_alloc) {
+            active_members_alloc *= 2;
+            active_members_lst_heap =
+                g_renew(const char *, active_members_lst_heap, active_members_alloc);
+            if (active_members_lst == active_members_lst_stack) {
+                memcpy(active_members_lst_heap,
+                       active_members_lst_stack,
+                       sizeof(const char *) * active_members_n);
+            }
+            active_members_lst = active_members_lst_heap;
+        }
+
+        active_members_lst[active_members_n++] = plink_port->name;
+    }
+
+    if (active_members_n > 0) {
+        gsize i;
+        gsize j;
+
+        /* We sort the active members by name */
+        g_qsort_with_data(active_members_lst,
+                          active_members_n,
+                          sizeof(const char *),
+                          nm_strcmp_p_with_data,
+                          NULL);
+
+        /* There really shouldn't be any duplicates. Nonetheless, check
+         * and drop them. They must be unique, because nm_firewall_nft_stdio_mlag()
+         * relies on that. */
+        for (j = 1, i = 1; i < active_members_n; i++) {
+            if (nm_streq(active_members_lst[j - 1], active_members_lst[i])) {
+                /* Repeated. Skip. */
+                continue;
+            }
+            if (j != i)
+                active_members_lst[j] = active_members_lst[i];
+            j++;
+        }
+        active_members_n = j;
+
+        active_members_result = g_new(const char *, active_members_n + 1u);
+        j                     = 0;
+
+        if (self->dat.active_members_curr) {
+            /* We configured a list earlier. We want to preserve the sort order
+             * from before. Prefer entries that we already had, in their previous
+             * order. */
+            for (i = 0; self->dat.active_members_curr[i]; i++) {
+                gssize idx;
+
+                /* We cannot use binary search, because we steal the elements we found
+                 * already. Hence this is O(n^2). We could use binary search if we would
+                 * not modify active_members_lst, but then we would need to remember
+                 * somehow which elements are already consumed. */
+                idx = nm_strv_find_first(active_members_lst,
+                                         active_members_n,
+                                         self->dat.active_members_curr[i]);
+                if (idx >= 0)
+                    active_members_result[j++] = g_steal_pointer(&active_members_lst[idx]);
+            }
+        }
+
+        /* append the remaining entries, which are sorted by name. */
+        for (i = 0; i < active_members_n; i++) {
+            if (active_members_lst[i])
+                active_members_result[j++] = active_members_lst[i];
+        }
+
+        nm_assert(j == active_members_n);
+        active_members_result[j] = NULL;
+    }
+
+    bond_ifname = plink_ctrl->name;
+
+out:
+    _reconfigure_do(self, reapply, bond_ifname, g_steal_pointer(&active_members_result));
+}
+
+static gboolean
+_reconfigure_check_on_idle_cb(gpointer user_data)
+{
+    NMBondManager *self = user_data;
+
+    nm_assert(!self->nft_in_progress);
+    _reconfigure_check(self, FALSE);
+    return G_SOURCE_CONTINUE;
+}
+
+/*****************************************************************************/
+
+static void
+_link_changed_cb(NMPlatform           *platform,
+                 int                   obj_type_i,
+                 int                   ifindex,
+                 const NMPlatformLink *plink,
+                 int                   change_type_i,
+                 NMBondManager        *self)
+{
+    if (self->reconfigure_check) {
+        /* Recheck already scheduled. */
+        return;
+    }
+
+    if (self->destroyed) {
+        /* We should not get another event at this point. Anyway, ignore. */
+        return;
+    }
+
+    if (ifindex == self->ifindex)
+        goto schedule;
+
+    if (plink->master == self->ifindex)
+        goto schedule;
+
+    if (g_hash_table_contains(self->previous_ifindexes, GINT_TO_POINTER(ifindex)))
+        goto schedule;
+
+    /* This event is not relevant. Skip. */
+    return;
+
+schedule:
+    self->reconfigure_check = TRUE;
+    if (!self->nft_in_progress) {
+        self->reconfigure_on_idle_source =
+            nm_g_idle_add_source(_reconfigure_check_on_idle_cb, self);
+    }
+}
+
+/*****************************************************************************/
+
+void
+nm_bond_manager_reapply(NMBondManager *self)
+{
+    _reconfigure_check(self, TRUE);
+}
+
+/*****************************************************************************/
+
+int
+nm_bond_manager_get_ifindex(NMBondManager *self)
+{
+    nm_assert(NM_IS_BOND_MANAGER(self));
+
+    return self->ifindex;
+}
+
+const char *
+nm_bond_manager_get_connection_uuid(NMBondManager *self)
+{
+    nm_assert(NM_IS_BOND_MANAGER(self));
+
+    return self->connection_uuid;
+}
+
+NMOptionBool
+nm_bond_manager_get_state(NMBondManager *self)
+{
+    nm_assert(NM_IS_BOND_MANAGER(self));
+
+    return self->state;
+}
+
+/*****************************************************************************/
+
+NMBondManager *
+nm_bond_manager_new(struct _NMPlatform   *platform,
+                    int                   ifindex,
+                    const char           *connection_uuid,
+                    NMBondManagerCallback callback,
+                    gpointer              user_data)
+{
+    NMBondManager *self;
+
+    nm_assert(NM_IS_PLATFORM(platform));
+    nm_assert(ifindex > 0);
+
+    self  = g_slice_new(NMBondManager);
+    *self = (NMBondManager){
+        .platform           = g_object_ref(platform),
+        .ifindex            = ifindex,
+        .reg_state          = REGISTRATION_STATE_NONE,
+        .destroyed          = FALSE,
+        .nft_good           = TRUE,
+        .callback           = callback,
+        .user_data          = user_data,
+        .previous_ifindexes = g_hash_table_new(nm_direct_hash, NULL),
+        .previous_members   = g_hash_table_new_full(nm_str_hash, g_str_equal, g_free, NULL),
+        .connection_uuid    = g_strdup(connection_uuid),
+        .state              = NM_OPTION_BOOL_DEFAULT,
+    };
+
+    self->link_changed_id = g_signal_connect(self->platform,
+                                             NM_PLATFORM_SIGNAL_LINK_CHANGED,
+                                             G_CALLBACK(_link_changed_cb),
+                                             self);
+
+    _LOGT("new balance-slb (MLAG) manager for interface %d", self->ifindex);
+
+    _reconfigure_check(self, TRUE);
+
+    return self;
+}
+
+void
+nm_bond_manager_destroy(NMBondManager *self)
+{
+    g_return_if_fail(self);
+    g_return_if_fail(!self->destroyed);
+
+    self->destroyed = TRUE;
+
+    self->callback  = NULL;
+    self->user_data = NULL;
+
+    nm_clear_g_signal_handler(self->platform, &self->link_changed_id);
+
+    nm_clear_g_source_inst(&self->reconfigure_on_idle_source);
+    self->reconfigure_check = FALSE;
+
+    nm_clear_g_free(&self->dat.bond_ifname_next);
+    nm_clear_g_free(&self->dat.active_members_next);
+
+    switch (self->reg_state) {
+    case REGISTRATION_STATE_NONE:
+        break;
+    case REGISTRATION_STATE_UPPING:
+        /* We still have some nfts registered. We need to wrap them up. */
+        _LOGT("destroying but deconfigure pending configuration first");
+        nm_clear_g_free(&self->dat.bond_ifname_next);
+        nm_clear_g_free(&self->dat.active_members_next);
+        nm_clear_g_cancellable(&self->cancellable);
+        return;
+    case REGISTRATION_STATE_UP:
+        _LOGT("destroying but deconfigure first");
+        _nft_call(self, FALSE, self->dat.bond_ifname_curr, NULL, NULL);
+        self->reg_state = REGISTRATION_STATE_DOWNING;
+        return;
+    case REGISTRATION_STATE_DOWNING:
+        _LOGT("destroying but wait for deconfiguring");
+        return;
+    }
+
+    _bond_manager_destroy(self);
+}
+
+static void
+_bond_manager_destroy(NMBondManager *self)
+{
+    _LOGT("destroyed");
+
+    nm_assert(self);
+    nm_assert(self->destroyed);
+    nm_assert(self->reg_state == REGISTRATION_STATE_NONE);
+    nm_assert(self->link_changed_id == 0);
+    nm_assert(!self->cancellable);
+    nm_assert(!self->dat.bond_ifname_curr);
+    nm_assert(!self->dat.active_members_curr);
+    nm_assert(!self->reconfigure_on_idle_source);
+
+    nm_clear_g_free(&self->dat.bond_ifname_next);
+    nm_clear_g_free(&self->dat.active_members_next);
+
+    g_object_unref(self->platform);
+    g_hash_table_unref(self->previous_ifindexes);
+    g_hash_table_unref(self->previous_members);
+    g_free(self->connection_uuid);
+    nm_g_slice_free(self);
+}
diff --git a/src/core/nm-bond-manager.h b/src/core/nm-bond-manager.h
new file mode 100644
index 0000000000..92a89f0b92
--- /dev/null
+++ b/src/core/nm-bond-manager.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#ifndef __NM_BOND_MANAGER_H__
+#define __NM_BOND_MANAGER_H__
+
+typedef struct _NMBondManager NMBondManager;
+
+struct _NMPlatform;
+
+typedef enum {
+    NM_BOND_MANAGER_EVENT_TYPE_STATE,
+} NMBondManagerEventType;
+
+typedef void (*NMBondManagerCallback)(NMBondManager         *self,
+                                      NMBondManagerEventType event_type,
+                                      gpointer               user_data);
+
+NMBondManager *nm_bond_manager_new(struct _NMPlatform   *platform,
+                                   int                   ifindex,
+                                   const char           *connection_uuid,
+                                   NMBondManagerCallback callback,
+                                   gpointer              user_data);
+
+void nm_bond_manager_reapply(NMBondManager *self);
+
+void nm_bond_manager_destroy(NMBondManager *self);
+
+int          nm_bond_manager_get_ifindex(NMBondManager *self);
+const char  *nm_bond_manager_get_connection_uuid(NMBondManager *self);
+NMOptionBool nm_bond_manager_get_state(NMBondManager *self);
+
+#endif /* __NM_BOND_MANAGER_H__ */