The existing rte_eth_set_queue_rate_limit() API allows setting a
per-queue Tx rate but provides no way to read it back. Applications
such as grout are forced to maintain a shadow copy of the rate to
be able to report it.

Add rte_eth_get_queue_rate_limit() as the symmetric getter, following
the established DPDK pattern (e.g. rte_eth_dev_set_mtu/get_mtu,
rte_eth_dev_set_vlan_offload/get_vlan_offload).

This adds:
- eth_get_queue_rate_limit_t driver callback in ethdev_driver.h
- rte_eth_get_queue_rate_limit() public experimental API (26.07)
- mlx5 PMD implementation reading from the existing per-queue
  rate_mbps tracking field

Signed-off-by: Vincent Jardin <[email protected]>
---
 app/test-pmd/cmdline.c      | 69 +++++++++++++++++++++++++++++++++++++
 drivers/net/mlx5/mlx5.c     |  2 ++
 drivers/net/mlx5/mlx5_tx.h  |  2 ++
 drivers/net/mlx5/mlx5_txq.c | 30 ++++++++++++++++
 lib/ethdev/ethdev_driver.h  |  7 ++++
 lib/ethdev/rte_ethdev.c     | 28 +++++++++++++++
 lib/ethdev/rte_ethdev.h     | 24 +++++++++++++
 7 files changed, 162 insertions(+)

diff --git a/app/test-pmd/cmdline.c b/app/test-pmd/cmdline.c
index c33c66f327..ee532984e8 100644
--- a/app/test-pmd/cmdline.c
+++ b/app/test-pmd/cmdline.c
@@ -8912,6 +8912,74 @@ static cmdline_parse_inst_t cmd_queue_rate_limit = {
        },
 };
 
+/* *** SHOW RATE LIMIT FOR A QUEUE OF A PORT *** */
+struct cmd_show_queue_rate_limit_result {
+       cmdline_fixed_string_t show;
+       cmdline_fixed_string_t port;
+       uint16_t port_num;
+       cmdline_fixed_string_t queue;
+       uint16_t queue_num;
+       cmdline_fixed_string_t rate;
+};
+
+static void cmd_show_queue_rate_limit_parsed(void *parsed_result,
+               __rte_unused struct cmdline *cl,
+               __rte_unused void *data)
+{
+       struct cmd_show_queue_rate_limit_result *res = parsed_result;
+       uint32_t tx_rate = 0;
+       int ret;
+
+       ret = rte_eth_get_queue_rate_limit(res->port_num, res->queue_num,
+                                          &tx_rate);
+       if (ret) {
+               fprintf(stderr, "Get queue rate limit failed: %s\n",
+                       rte_strerror(-ret));
+               return;
+       }
+       if (tx_rate)
+               printf("Port %u Queue %u rate limit: %u Mbps\n",
+                      res->port_num, res->queue_num, tx_rate);
+       else
+               printf("Port %u Queue %u rate limit: disabled\n",
+                      res->port_num, res->queue_num);
+}
+
+static cmdline_parse_token_string_t cmd_show_queue_rate_limit_show =
+       TOKEN_STRING_INITIALIZER(struct cmd_show_queue_rate_limit_result,
+                               show, "show");
+static cmdline_parse_token_string_t cmd_show_queue_rate_limit_port =
+       TOKEN_STRING_INITIALIZER(struct cmd_show_queue_rate_limit_result,
+                               port, "port");
+static cmdline_parse_token_num_t cmd_show_queue_rate_limit_portnum =
+       TOKEN_NUM_INITIALIZER(struct cmd_show_queue_rate_limit_result,
+                               port_num, RTE_UINT16);
+static cmdline_parse_token_string_t cmd_show_queue_rate_limit_queue =
+       TOKEN_STRING_INITIALIZER(struct cmd_show_queue_rate_limit_result,
+                               queue, "queue");
+static cmdline_parse_token_num_t cmd_show_queue_rate_limit_queuenum =
+       TOKEN_NUM_INITIALIZER(struct cmd_show_queue_rate_limit_result,
+                               queue_num, RTE_UINT16);
+static cmdline_parse_token_string_t cmd_show_queue_rate_limit_rate =
+       TOKEN_STRING_INITIALIZER(struct cmd_show_queue_rate_limit_result,
+                               rate, "rate");
+
+static cmdline_parse_inst_t cmd_show_queue_rate_limit = {
+       .f = cmd_show_queue_rate_limit_parsed,
+       .data = NULL,
+       .help_str = "show port <port_id> queue <queue_id> rate: "
+               "Show rate limit for a queue on port_id",
+       .tokens = {
+               (void *)&cmd_show_queue_rate_limit_show,
+               (void *)&cmd_show_queue_rate_limit_port,
+               (void *)&cmd_show_queue_rate_limit_portnum,
+               (void *)&cmd_show_queue_rate_limit_queue,
+               (void *)&cmd_show_queue_rate_limit_queuenum,
+               (void *)&cmd_show_queue_rate_limit_rate,
+               NULL,
+       },
+};
+
 /* *** SET RATE LIMIT FOR A VF OF A PORT *** */
 struct cmd_vf_rate_limit_result {
        cmdline_fixed_string_t set;
@@ -14198,6 +14266,7 @@ static cmdline_parse_ctx_t builtin_ctx[] = {
        &cmd_set_uc_all_hash_filter,
        &cmd_vf_mac_addr_filter,
        &cmd_queue_rate_limit,
+       &cmd_show_queue_rate_limit,
        &cmd_tunnel_udp_config,
        &cmd_showport_rss_hash,
        &cmd_showport_rss_hash_key,
diff --git a/drivers/net/mlx5/mlx5.c b/drivers/net/mlx5/mlx5.c
index f399e0d5c9..6e21ed31f3 100644
--- a/drivers/net/mlx5/mlx5.c
+++ b/drivers/net/mlx5/mlx5.c
@@ -2721,6 +2721,7 @@ const struct eth_dev_ops mlx5_dev_ops = {
        .rx_metadata_negotiate = mlx5_flow_rx_metadata_negotiate,
        .get_restore_flags = mlx5_get_restore_flags,
        .set_queue_rate_limit = mlx5_set_queue_rate_limit,
+       .get_queue_rate_limit = mlx5_get_queue_rate_limit,
 };
 
 /* Available operations from secondary process. */
@@ -2815,6 +2816,7 @@ const struct eth_dev_ops mlx5_dev_ops_isolate = {
        .map_aggr_tx_affinity = mlx5_map_aggr_tx_affinity,
        .get_restore_flags = mlx5_get_restore_flags,
        .set_queue_rate_limit = mlx5_set_queue_rate_limit,
+       .get_queue_rate_limit = mlx5_get_queue_rate_limit,
 };
 
 /**
diff --git a/drivers/net/mlx5/mlx5_tx.h b/drivers/net/mlx5/mlx5_tx.h
index 3a37f5bb4d..46e199d93e 100644
--- a/drivers/net/mlx5/mlx5_tx.h
+++ b/drivers/net/mlx5/mlx5_tx.h
@@ -224,6 +224,8 @@ int mlx5_txq_releasable(struct rte_eth_dev *dev, uint16_t 
idx);
 int mlx5_txq_verify(struct rte_eth_dev *dev);
 int mlx5_set_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
                              uint32_t tx_rate);
+int mlx5_get_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
+                             uint32_t *tx_rate);
 int mlx5_txq_get_sqn(struct mlx5_txq_ctrl *txq);
 void mlx5_txq_alloc_elts(struct mlx5_txq_ctrl *txq_ctrl);
 void mlx5_txq_free_elts(struct mlx5_txq_ctrl *txq_ctrl);
diff --git a/drivers/net/mlx5/mlx5_txq.c b/drivers/net/mlx5/mlx5_txq.c
index f0881f3560..c81542113e 100644
--- a/drivers/net/mlx5/mlx5_txq.c
+++ b/drivers/net/mlx5/mlx5_txq.c
@@ -1473,6 +1473,36 @@ mlx5_set_queue_rate_limit(struct rte_eth_dev *dev, 
uint16_t queue_idx,
        return 0;
 }
 
+/**
+ * Get per-queue packet pacing rate limit.
+ *
+ * @param dev
+ *   Pointer to Ethernet device.
+ * @param queue_idx
+ *   TX queue index.
+ * @param[out] tx_rate
+ *   Pointer to store the TX rate in Mbps, 0 if rate limiting is disabled.
+ *
+ * @return
+ *   0 on success, a negative errno value otherwise and rte_errno is set.
+ */
+int
+mlx5_get_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
+                         uint32_t *tx_rate)
+{
+       struct mlx5_priv *priv = dev->data->dev_private;
+       struct mlx5_txq_ctrl *txq_ctrl;
+
+       if (priv->txqs == NULL || (*priv->txqs)[queue_idx] == NULL) {
+               rte_errno = EINVAL;
+               return -rte_errno;
+       }
+       txq_ctrl = container_of((*priv->txqs)[queue_idx],
+                               struct mlx5_txq_ctrl, txq);
+       *tx_rate = txq_ctrl->rl.rate_mbps;
+       return 0;
+}
+
 /**
  * Verify if the queue can be released.
  *
diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
index 1255cd6f2c..0f336f9567 100644
--- a/lib/ethdev/ethdev_driver.h
+++ b/lib/ethdev/ethdev_driver.h
@@ -762,6 +762,11 @@ typedef int (*eth_set_queue_rate_limit_t)(struct 
rte_eth_dev *dev,
                                uint16_t queue_idx,
                                uint32_t tx_rate);
 
+/** @internal Get queue Tx rate. */
+typedef int (*eth_get_queue_rate_limit_t)(struct rte_eth_dev *dev,
+                               uint16_t queue_idx,
+                               uint32_t *tx_rate);
+
 /** @internal Add tunneling UDP port. */
 typedef int (*eth_udp_tunnel_port_add_t)(struct rte_eth_dev *dev,
                                         struct rte_eth_udp_tunnel *tunnel_udp);
@@ -1522,6 +1527,8 @@ struct eth_dev_ops {
 
        /** Set queue rate limit */
        eth_set_queue_rate_limit_t set_queue_rate_limit;
+       /** Get queue rate limit */
+       eth_get_queue_rate_limit_t get_queue_rate_limit;
 
        /** Configure RSS hash protocols and hashing key */
        rss_hash_update_t          rss_hash_update;
diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
index 2edc7a362e..c6ad399033 100644
--- a/lib/ethdev/rte_ethdev.c
+++ b/lib/ethdev/rte_ethdev.c
@@ -5694,6 +5694,34 @@ int rte_eth_set_queue_rate_limit(uint16_t port_id, 
uint16_t queue_idx,
        return ret;
 }
 
+RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_eth_get_queue_rate_limit, 26.07)
+int rte_eth_get_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
+                                       uint32_t *tx_rate)
+{
+       struct rte_eth_dev *dev;
+
+       RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
+       dev = &rte_eth_devices[port_id];
+
+       if (tx_rate == NULL) {
+               RTE_ETHDEV_LOG_LINE(ERR,
+                       "Get queue rate limit:port %u: NULL tx_rate pointer",
+                       port_id);
+               return -EINVAL;
+       }
+
+       if (queue_idx >= dev->data->nb_tx_queues) {
+               RTE_ETHDEV_LOG_LINE(ERR,
+                       "Get queue rate limit:port %u: invalid queue ID=%u",
+                       port_id, queue_idx);
+               return -EINVAL;
+       }
+
+       if (dev->dev_ops->get_queue_rate_limit == NULL)
+               return -ENOTSUP;
+       return eth_err(port_id, dev->dev_ops->get_queue_rate_limit(dev, 
queue_idx, tx_rate));
+}
+
 RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_eth_rx_avail_thresh_set, 22.07)
 int rte_eth_rx_avail_thresh_set(uint16_t port_id, uint16_t queue_id,
                               uint8_t avail_thresh)
diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
index 0d8e2d0236..e525217b77 100644
--- a/lib/ethdev/rte_ethdev.h
+++ b/lib/ethdev/rte_ethdev.h
@@ -4817,6 +4817,30 @@ int rte_eth_dev_uc_all_hash_table_set(uint16_t port_id, 
uint8_t on);
 int rte_eth_set_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
                        uint32_t tx_rate);
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice.
+ *
+ * Get the rate limitation for a queue on an Ethernet device.
+ *
+ * @param port_id
+ *   The port identifier of the Ethernet device.
+ * @param queue_idx
+ *   The queue ID.
+ * @param[out] tx_rate
+ *   A pointer to retrieve the Tx rate in Mbps.
+ *   0 means rate limiting is disabled.
+ * @return
+ *   - (0) if successful.
+ *   - (-ENOTSUP) if hardware doesn't support this feature.
+ *   - (-ENODEV) if *port_id* invalid.
+ *   - (-EIO) if device is removed.
+ *   - (-EINVAL) if bad parameter.
+ */
+__rte_experimental
+int rte_eth_get_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
+                       uint32_t *tx_rate);
+
 /**
  * Configuration of Receive Side Scaling hash computation of Ethernet device.
  *
-- 
2.43.0

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