[PATCH net-next v2 v2 1/2] net: mctp-i2c: notify user space on TX failure

[PATCH net-next v2 v2 1/2] net: mctp-i2c: notify user space on TX failure

[Jian Zhang]

Report local transmit errors from the MCTP I2C transport using
sock_queue_err_skb(), allowing the socket layer to be notified
of failed transmissions.

Signed-off-by: Jian Zhang <zhangjian.3032@bytedance.com>
---
Changelog v2:
- use sock_queue_err_skb() instead of sk_error_report()
- link to v1: https://lore.kernel.org/all/20241108094206.2808293-1-zhangjian.3032@bytedance.com/

 drivers/net/mctp/mctp-i2c.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mctp/mctp-i2c.c b/drivers/net/mctp/mctp-i2c.c
index f782d93f826e..f6e329b66240 100644
--- a/drivers/net/mctp/mctp-i2c.c
+++ b/drivers/net/mctp/mctp-i2c.c
@@ -24,6 +24,7 @@
 #include <linux/if_arp.h>
 #include <net/mctp.h>
 #include <net/mctpdevice.h>
+#include <linux/errqueue.h>
 
 /* byte_count is limited to u8 */
 #define MCTP_I2C_MAXBLOCK 255
@@ -477,6 +478,23 @@ static void mctp_i2c_invalidate_tx_flow(struct mctp_i2c_dev *midev,
 		mctp_i2c_unlock_nest(midev);
 }
 
+static void mctp_i2c_report_error(struct sock *sk, struct sk_buff *skb, int rc)
+{
+	struct sock_exterr_skb *serr;
+
+	skb = skb_clone(skb, GFP_ATOMIC);
+	if (!skb)
+		return;
+
+	serr = SKB_EXT_ERR(skb);
+	memset(serr, 0, sizeof(*serr));
+	serr->ee.ee_errno = -rc;
+	serr->ee.ee_origin = SO_EE_ORIGIN_LOCAL;
+
+	if (sock_queue_err_skb(sk, skb))
+		kfree_skb(skb);
+}
+
 static void mctp_i2c_xmit(struct mctp_i2c_dev *midev, struct sk_buff *skb)
 {
 	struct net_device_stats *stats = &midev->ndev->stats;
@@ -537,8 +555,11 @@ static void mctp_i2c_xmit(struct mctp_i2c_dev *midev, struct sk_buff *skb)
 		rc = __i2c_transfer(midev->adapter, &msg, 1);
 
 		/* on tx errors, the flow can no longer be considered valid */
-		if (rc < 0)
+		if (rc < 0) {
 			mctp_i2c_invalidate_tx_flow(midev, skb);
+			if (skb->sk)
+				mctp_i2c_report_error(skb->sk, skb, rc);
+		}
 
 		break;
 
-- 
2.20.1

Re: [PATCH net-next v2 v2 1/2] net: mctp-i2c: notify user space on TX failure

[Jakub Kicinski]

On Fri, 16 Jan 2026 16:58:39 +0800 Jian Zhang wrote:
> Report local transmit errors from the MCTP I2C transport using
> sock_queue_err_skb(), allowing the socket layer to be notified
> of failed transmissions.

Shouldn't you hide this behind a setsockopt() knob?
Existing applications will not expect having to service the error queue.
-- 
pw-bot: cr