On 7/22/26 7:49 AM, Han Zhou wrote:
> OVS 3.7 (OVS commit 3900653) increased FLOW_N_REGS from 16 to 32, making
> registers reg16..reg31 (xxreg4..xxreg7) usable. However, whether the
> running ovs-vswitchd actually supports them depends on its version, so
> OVN must detect this at runtime before relying on those registers.
>
> Add an OVS OpenFlow feature probe (OVS_REG32_SUPPORT) that pushes a
> discarded bundle containing a flow_mod matching reg16. An ovs-vswitchd
> that does not support 32 registers rejects it with an error; a newer one
> accepts it, so the barrier is reached without error.
>
> ovn-controller advertises the result to the SB Chassis via
> other_config:ovn-32-registers, and ovn-northd aggregates it across all
> local chassis into chassis_features.reg32. This lets later features use
> registers beyond reg15 only when every chassis supports them, and fall
> back otherwise.
>
> Assisted-by: Claude Opus 4.8, Cursor
> Signed-off-by: Han Zhou <[email protected]>
> ---
Hi Han,
This is not really needed for the "Support per-route VNI for learned
EVPN routes." patch-set as I see you reworked it without new registers.
But I think it would be a nice to have feature. I'm sure we will need
the detection mechanism in the near future.
Do you mind posting this one separately as a regular patch?
Regards,
Dumitru
> controller/chassis.c | 12 +++++++
> include/ovn/features.h | 6 ++++
> lib/features.c | 75 +++++++++++++++++++++++++++++++++++++++
> northd/en-global-config.c | 13 +++++++
> northd/en-global-config.h | 1 +
> 5 files changed, 107 insertions(+)
>
> diff --git a/controller/chassis.c b/controller/chassis.c
> index 0e3bd37d8752..2160c84d5c91 100644
> --- a/controller/chassis.c
> +++ b/controller/chassis.c
> @@ -74,6 +74,8 @@ struct ovs_chassis_cfg {
> bool sample_with_regs;
> /* Does OVS support flushing CT zones using label/mark? */
> bool ct_label_flush;
> + /* Does OVS support 32 registers (reg16..reg31)? */
> + bool reg32;
> };
>
> enum chassis_update_status {
> @@ -385,6 +387,7 @@ chassis_parse_ovs_config(const struct
> ovsrec_open_vswitch_table *ovs_table,
> ovs_feature_is_supported(OVS_SAMPLE_REG_SUPPORT);
> ovs_cfg->ct_label_flush =
> ovs_feature_is_supported(OVS_CT_LABEL_FLUSH_SUPPORT);
> + ovs_cfg->reg32 = ovs_feature_is_supported(OVS_REG32_SUPPORT);
>
> return true;
> }
> @@ -424,6 +427,8 @@ chassis_build_other_config(const struct ovs_chassis_cfg
> *ovs_cfg,
> smap_replace(config, OVN_FEATURE_CT_LABEL_FLUSH,
> ovs_cfg->ct_label_flush ? "true" :"false");
> smap_replace(config, OVN_FEATURE_CT_STATE_SAVE, "true");
> + smap_replace(config, OVN_FEATURE_REG32,
> + ovs_cfg->reg32 ? "true" : "false");
> }
>
> /*
> @@ -597,6 +602,12 @@ chassis_other_config_changed(const struct
> ovs_chassis_cfg *ovs_cfg,
> return true;
> }
>
> + bool chassis_reg32 =
> + smap_get_bool(&chassis_rec->other_config, OVN_FEATURE_REG32, false);
> + if (chassis_reg32 != ovs_cfg->reg32) {
> + return true;
> + }
> +
> return false;
> }
>
> @@ -779,6 +790,7 @@ update_supported_sset(struct sset *supported)
> sset_add(supported, OVN_FEATURE_CT_NEXT_ZONE);
> sset_add(supported, OVN_FEATURE_CT_LABEL_FLUSH);
> sset_add(supported, OVN_FEATURE_CT_STATE_SAVE);
> + sset_add(supported, OVN_FEATURE_REG32);
> }
>
> static void
> diff --git a/include/ovn/features.h b/include/ovn/features.h
> index 7207da67fd20..bb7c85ea5cff 100644
> --- a/include/ovn/features.h
> +++ b/include/ovn/features.h
> @@ -27,6 +27,7 @@
> #define OVN_FEATURE_CT_NEXT_ZONE "ct-next-zone"
> #define OVN_FEATURE_CT_LABEL_FLUSH "ct-label-flush"
> #define OVN_FEATURE_CT_STATE_SAVE "ct-state-save"
> +#define OVN_FEATURE_REG32 "ovn-32-registers"
>
> /* DEPRECATED: The following features can be removed
> * after the next LTS version release. */
> @@ -45,6 +46,7 @@ enum ovs_feature_support_bits {
> OVS_OF_GROUP_SUPPORT_BIT,
> OVS_SAMPLE_REG_SUPPORT_BIT,
> OVS_CT_LABEL_FLUSH_BIT,
> + OVS_REG32_SUPPORT_BIT,
> };
>
> enum ovs_feature_value {
> @@ -55,6 +57,10 @@ enum ovs_feature_value {
> OVS_OF_GROUP_SUPPORT = (1 << OVS_OF_GROUP_SUPPORT_BIT),
> OVS_SAMPLE_REG_SUPPORT = (1 << OVS_SAMPLE_REG_SUPPORT_BIT),
> OVS_CT_LABEL_FLUSH_SUPPORT = (1 << OVS_CT_LABEL_FLUSH_BIT),
> + /* OVS (and its OpenFlow interface) supports 32 32-bit registers,
> + * i.e. registers reg16..reg31 (xxreg4..xxreg7) are usable. Older OVS
> + * versions only support 16 registers. */
> + OVS_REG32_SUPPORT = (1 << OVS_REG32_SUPPORT_BIT),
> };
>
> void ovs_feature_support_destroy(void);
> diff --git a/lib/features.c b/lib/features.c
> index 7bee1c3806e6..b787bf7e8529 100644
> --- a/lib/features.c
> +++ b/lib/features.c
> @@ -269,6 +269,73 @@ sample_with_reg_handle_barrier(struct
> ovs_openflow_feature *feature OVS_UNUSED)
> return true;
> }
>
> +static void
> +reg32_send_request(struct ovs_openflow_feature *feature)
> +{
> + struct ofputil_bundle_ctrl_msg ctrl = {
> + .bundle_id = 0,
> + .flags = OFPBF_ORDERED | OFPBF_ATOMIC,
> + .type = OFPBCT_OPEN_REQUEST,
> + };
> + rconn_send(swconn,
> + ofputil_encode_bundle_ctrl_request(OFP15_VERSION, &ctrl),
> NULL);
> +
> + struct ofputil_flow_mod fm = {
> + .priority = 0,
> + .table_id = 0,
> + .ofpacts = NULL,
> + .ofpacts_len = 0,
> + .command = OFPFC_ADD,
> + .new_cookie = htonll(0),
> + .buffer_id = UINT32_MAX,
> + .out_port = OFPP_ANY,
> + .out_group = OFPG_ANY,
> + };
> +
> + /* Match on reg16, which only exists when the running OVS supports 32
> + * registers. Older OVS versions reject the flow_mod with an error. */
> + struct match match;
> + match_init_catchall(&match);
> + match_set_reg(&match, MFF_REG16 - MFF_REG0, 1);
> + minimatch_init(&fm.match, &match);
> +
> + struct ofpbuf *fm_msg = ofputil_encode_flow_mod(&fm, OFPUTIL_P_OF15_OXM);
> +
> + struct ofputil_bundle_add_msg bam = {
> + .bundle_id = ctrl.bundle_id,
> + .flags = ctrl.flags,
> + .msg = fm_msg->data,
> + };
> + struct ofpbuf *msg = ofputil_encode_bundle_add(OFP15_VERSION, &bam);
> +
> + feature->xid = ((struct ofp_header *) msg->data)->xid;
> + rconn_send(swconn, msg, NULL);
> +
> + ctrl.type = OFPBCT_DISCARD_REQUEST;
> + rconn_send(swconn,
> + ofputil_encode_bundle_ctrl_request(OFP15_VERSION, &ctrl),
> NULL);
> +
> + minimatch_destroy(&fm.match);
> + ofpbuf_delete(fm_msg);
> +}
> +
> +static bool
> +reg32_handle_response(struct ovs_openflow_feature *feature,
> + enum ofptype type, const struct ofp_header *oh)
> +{
> + if (type != OFPTYPE_ERROR) {
> + log_unexpected_reply(feature, oh);
> + }
> +
> + return false;
> +}
> +
> +static bool
> +reg32_handle_barrier(struct ovs_openflow_feature *feature OVS_UNUSED)
> +{
> + return true;
> +}
> +
> static void
> ct_label_flush_send_request(struct ovs_openflow_feature *feature)
> {
> @@ -345,6 +412,13 @@ static struct ovs_openflow_feature
> all_openflow_features[] = {
> .handle_response = ct_label_flush_handle_response,
> .handle_barrier = ct_label_flush_handle_barrier,
> },
> + {
> + .value = OVS_REG32_SUPPORT,
> + .name = "reg32",
> + .send_request = reg32_send_request,
> + .handle_response = reg32_handle_response,
> + .handle_barrier = reg32_handle_barrier,
> + },
> };
>
> static bool
> @@ -418,6 +492,7 @@ ovs_feature_is_valid(enum ovs_feature_value feature)
> case OVS_OF_GROUP_SUPPORT:
> case OVS_SAMPLE_REG_SUPPORT:
> case OVS_CT_LABEL_FLUSH_SUPPORT:
> + case OVS_REG32_SUPPORT:
> return true;
> default:
> return false;
> diff --git a/northd/en-global-config.c b/northd/en-global-config.c
> index 4e6b07ebe50e..0667e11ffe8a 100644
> --- a/northd/en-global-config.c
> +++ b/northd/en-global-config.c
> @@ -520,6 +520,7 @@ northd_enable_all_features(struct ed_type_global_config
> *data)
> .ct_next_zone = true,
> .ct_label_flush = true,
> .ct_state_save = true,
> + .reg32 = true,
> };
> }
>
> @@ -590,6 +591,14 @@ build_chassis_features(const struct sbrec_chassis_table
> *sbrec_chassis_table,
> chassis_features->ct_state_save) {
> chassis_features->ct_state_save = false;
> }
> +
> + bool reg32 =
> + smap_get_bool(&chassis->other_config,
> + OVN_FEATURE_REG32,
> + false);
> + if (!reg32 && chassis_features->reg32) {
> + chassis_features->reg32 = false;
> + }
> }
> }
>
> @@ -747,6 +756,10 @@ chassis_features_changed(const struct chassis_features
> *present,
> return true;
> }
>
> + if (present->reg32 != updated->reg32) {
> + return true;
> + }
> +
> return false;
> }
>
> diff --git a/northd/en-global-config.h b/northd/en-global-config.h
> index 5a7b7ecda766..9b75ecff3d21 100644
> --- a/northd/en-global-config.h
> +++ b/northd/en-global-config.h
> @@ -20,6 +20,7 @@ struct chassis_features {
> bool ct_next_zone;
> bool ct_label_flush;
> bool ct_state_save;
> + bool reg32;
> };
>
> struct global_config_tracked_data {
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