[PATCH net-next 48/48] can: netlink: add userland error messages

[Marc Kleine-Budde <mkl@pengutronix.de>]

From: Vincent Mailhol <mailhol@kernel.org>

Use NL_SET_ERR_MSG() and NL_SET_ERR_MSG_FMT() to return meaningful
error messages to the userland whenever a -EOPNOTSUPP error is
returned due to a failed validation of the CAN netlink arguments.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Link: https://patch.msgid.link/20250923-canxl-netlink-prep-v4-20-e720d28f66fe@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 drivers/net/can/dev/netlink.c | 82 ++++++++++++++++++++++++++---------
 1 file changed, 62 insertions(+), 20 deletions(-)

diff --git a/drivers/net/can/dev/netlink.c b/drivers/net/can/dev/netlink.c
index 92d8df13e886..0591406b6f32 100644
--- a/drivers/net/can/dev/netlink.c
+++ b/drivers/net/can/dev/netlink.c
@@ -64,15 +64,23 @@ static int can_validate_tdc(struct nlattr *data_tdc,
 	bool tdc_auto = tdc_flags & CAN_CTRLMODE_TDC_AUTO_MASK;
 	int err;
 
-	/* CAN_CTRLMODE_TDC_{AUTO,MANUAL} are mutually exclusive */
-	if (tdc_auto && tdc_manual)
+	if (tdc_auto && tdc_manual) {
+		NL_SET_ERR_MSG(extack,
+			       "TDC manual and auto modes are mutually exclusive");
 		return -EOPNOTSUPP;
+	}
 
 	/* If one of the CAN_CTRLMODE_TDC_* flag is set then TDC
 	 * must be set and vice-versa
 	 */
-	if ((tdc_auto || tdc_manual) != !!data_tdc)
+	if ((tdc_auto || tdc_manual) && !data_tdc) {
+		NL_SET_ERR_MSG(extack, "TDC parameters are missing");
 		return -EOPNOTSUPP;
+	}
+	if (!(tdc_auto || tdc_manual) && data_tdc) {
+		NL_SET_ERR_MSG(extack, "TDC mode (auto or manual) is missing");
+		return -EOPNOTSUPP;
+	}
 
 	/* If providing TDC parameters, at least TDCO is needed. TDCV
 	 * is needed if and only if CAN_CTRLMODE_TDC_MANUAL is set
@@ -86,15 +94,23 @@ static int can_validate_tdc(struct nlattr *data_tdc,
 			return err;
 
 		if (tb_tdc[IFLA_CAN_TDC_TDCV]) {
-			if (tdc_auto)
+			if (tdc_auto) {
+				NL_SET_ERR_MSG(extack,
+					       "TDCV is incompatible with TDC auto mode");
 				return -EOPNOTSUPP;
+			}
 		} else {
-			if (tdc_manual)
+			if (tdc_manual) {
+				NL_SET_ERR_MSG(extack,
+					       "TDC manual mode requires TDCV");
 				return -EOPNOTSUPP;
+			}
 		}
 
-		if (!tb_tdc[IFLA_CAN_TDC_TDCO])
+		if (!tb_tdc[IFLA_CAN_TDC_TDCO]) {
+			NL_SET_ERR_MSG(extack, "TDCO is missing");
 			return -EOPNOTSUPP;
+		}
 	}
 
 	return 0;
@@ -105,6 +121,7 @@ static int can_validate_databittiming(struct nlattr *data[],
 				      int ifla_can_data_bittiming, u32 flags)
 {
 	struct nlattr *data_tdc;
+	const char *type;
 	u32 tdc_flags;
 	bool is_on;
 	int err;
@@ -120,18 +137,31 @@ static int can_validate_databittiming(struct nlattr *data[],
 		data_tdc = data[IFLA_CAN_TDC];
 		tdc_flags = flags & CAN_CTRLMODE_FD_TDC_MASK;
 		is_on = flags & CAN_CTRLMODE_FD;
+		type = "FD";
 	} else {
 		return -EOPNOTSUPP; /* Place holder for CAN XL */
 	}
 
 	if (is_on) {
-		if (!data[IFLA_CAN_BITTIMING] || !data[ifla_can_data_bittiming])
+		if (!data[IFLA_CAN_BITTIMING] || !data[ifla_can_data_bittiming]) {
+			NL_SET_ERR_MSG_FMT(extack,
+					   "Provide both nominal and %s data bittiming",
+					   type);
 			return -EOPNOTSUPP;
-	}
-
-	if (data[ifla_can_data_bittiming] || data_tdc) {
-		if (!is_on)
+		}
+	} else {
+		if (data[ifla_can_data_bittiming]) {
+			NL_SET_ERR_MSG_FMT(extack,
+					   "%s data bittiming requires CAN %s",
+					   type, type);
 			return -EOPNOTSUPP;
+		}
+		if (data_tdc) {
+			NL_SET_ERR_MSG_FMT(extack,
+					   "%s TDC requires CAN %s",
+					   type, type);
+			return -EOPNOTSUPP;
+		}
 	}
 
 	err = can_validate_bittiming(data, extack, ifla_can_data_bittiming);
@@ -178,8 +208,7 @@ static int can_ctrlmode_changelink(struct net_device *dev,
 {
 	struct can_priv *priv = netdev_priv(dev);
 	struct can_ctrlmode *cm;
-	u32 maskedflags;
-	u32 ctrlstatic;
+	u32 ctrlstatic, maskedflags, notsupp, ctrlstatic_missing;
 
 	if (!data[IFLA_CAN_CTRLMODE])
 		return 0;
@@ -189,20 +218,28 @@ static int can_ctrlmode_changelink(struct net_device *dev,
 		return -EBUSY;
 
 	cm = nla_data(data[IFLA_CAN_CTRLMODE]);
-	maskedflags = cm->flags & cm->mask;
 	ctrlstatic = can_get_static_ctrlmode(priv);
+	maskedflags = cm->flags & cm->mask;
+	notsupp = maskedflags & ~(priv->ctrlmode_supported | ctrlstatic);
+	ctrlstatic_missing = (maskedflags & ctrlstatic) ^ ctrlstatic;
 
-	/* check whether provided bits are allowed to be passed */
-	if (maskedflags & ~(priv->ctrlmode_supported | ctrlstatic))
+	if (notsupp) {
+		NL_SET_ERR_MSG_FMT(extack,
+				   "requested control mode %s not supported",
+				   can_get_ctrlmode_str(notsupp));
 		return -EOPNOTSUPP;
+	}
 
 	/* do not check for static fd-non-iso if 'fd' is disabled */
 	if (!(maskedflags & CAN_CTRLMODE_FD))
 		ctrlstatic &= ~CAN_CTRLMODE_FD_NON_ISO;
 
-	/* make sure static options are provided by configuration */
-	if ((maskedflags & ctrlstatic) != ctrlstatic)
+	if (ctrlstatic_missing) {
+		NL_SET_ERR_MSG_FMT(extack,
+				   "missing required %s static control mode",
+				   can_get_ctrlmode_str(ctrlstatic_missing));
 		return -EOPNOTSUPP;
+	}
 
 	/* If a top dependency flag is provided, reset all its dependencies */
 	if (cm->mask & CAN_CTRLMODE_FD)
@@ -234,8 +271,10 @@ static int can_tdc_changelink(struct data_bittiming_params *dbt_params,
 	const struct can_tdc_const *tdc_const = dbt_params->tdc_const;
 	int err;
 
-	if (!tdc_const)
+	if (!tdc_const) {
+		NL_SET_ERR_MSG(extack, "The device does not support TDC");
 		return -EOPNOTSUPP;
+	}
 
 	err = nla_parse_nested(tb_tdc, IFLA_CAN_TDC_MAX, nla,
 			       can_tdc_policy, extack);
@@ -450,8 +489,11 @@ static int can_changelink(struct net_device *dev, struct nlattr *tb[],
 		const unsigned int num_term = priv->termination_const_cnt;
 		unsigned int i;
 
-		if (!priv->do_set_termination)
+		if (!priv->do_set_termination) {
+			NL_SET_ERR_MSG(extack,
+				       "Termination is not configurable on this device");
 			return -EOPNOTSUPP;
+		}
 
 		/* check whether given value is supported by the interface */
 		for (i = 0; i < num_term; i++) {
-- 
2.51.0