Re: [PATCH bpf-next] bpf: Pass extack to bpf_xdp_link_attach

[Alexei Starovoitov]

On Wed, Oct 21, 2026 at 08:24 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>  	case BPF_PROG_TYPE_XDP:
> -		ret = bpf_xdp_link_attach(attr, prog, log);
> +{
> +		struct netlink_ext_ack extack = {};
> +
> +		ret = bpf_xdp_link_attach(attr, prog, &extack);
> +		if (extack._msg)
> +			bpf_log(log, "%s\n", extack._msg);
>  		break;
> +}

CI is right. This looks odd,
but instead of CI's suggestion:
        case BPF_PROG_TYPE_XDP: {
                struct netlink_ext_ack extack = {};

do something like below:

sock_map, netkit and nf links will probably need the same when you
get to them. They can take &extack too.

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 1d34ece..5926f13 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1269,13 +1269,8 @@ __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,
 				      const char *fmt, va_list args);
 __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
 					   const char *fmt, ...);
-#ifdef CONFIG_BPF_SYSCALL
 __printf(2, 3) void bpf_log(struct bpf_verifier_log *log,
 			    const char *fmt, ...);
-#else
-__printf(2, 3) static inline void bpf_log(struct bpf_verifier_log *log,
-					  const char *fmt, ...) {}
-#endif
 int bpf_vlog_init(struct bpf_verifier_log *log, u32 log_level,
 		  char __user *log_buf, u32 log_size);
 void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos);
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4548b0f..f5d6438 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4418,7 +4418,7 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 				    struct netdev_queue *txq, int *ret);

 int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog,
-			struct bpf_verifier_log *log);
+			struct netlink_ext_ack *extack);
 u8 dev_xdp_prog_count(struct net_device *dev);
 int netif_xdp_propagate(struct net_device *dev, struct netdev_bpf *bpf);
 int dev_xdp_propagate(struct net_device *dev, struct netdev_bpf *bpf);
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 87cd122..0ce75ee 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5865,6 +5865,7 @@ err_put:
 static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_attr *attr_common,
 		       bpfptr_t uattr_common, u32 size_common)
 {
+	struct netlink_ext_ack extack = {};
 	struct bpf_verifier_log *log;
 	struct bpf_log_attr attr_log;
 	struct bpf_prog *prog;
@@ -5944,7 +5945,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a
 		break;
 #ifdef CONFIG_NET
 	case BPF_PROG_TYPE_XDP:
-		ret = bpf_xdp_link_attach(attr, prog, log);
+		ret = bpf_xdp_link_attach(attr, prog, &extack);
 		break;
 	case BPF_PROG_TYPE_SCHED_CLS:
 		if (attr->link_create.attach_type == BPF_TCX_INGRESS ||
@@ -5978,8 +5979,11 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a

 out:
 	if (ret < 0) {
-		int err = bpf_log_attr_finalize(&attr_log, log);
+		int err;

+		if (extack._msg)
+			bpf_log(log, "%s\n", extack._msg);
+		err = bpf_log_attr_finalize(&attr_log, log);
 		ret = err ? err : ret;
 		if (prog)
 			bpf_prog_put(prog);
diff --git a/net/core/dev.c b/net/core/dev.c
index a142613..d79a589 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -97,7 +97,6 @@
 #include <linux/kthread.h>
 #include <linux/bpf.h>
 #include <linux/bpf_trace.h>
-#include <linux/bpf_verifier.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 #include <net/busy_poll.h>
@@ -10773,11 +10772,10 @@ static const struct bpf_link_ops bpf_xdp_link_lops = {
 };

 int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog,
-			struct bpf_verifier_log *log)
+			struct netlink_ext_ack *extack)
 {
 	struct net *net = current->nsproxy->net_ns;
 	struct bpf_link_primer link_primer;
-	struct netlink_ext_ack extack = {};
 	struct bpf_xdp_link *link;
 	struct net_device *dev;
 	int err, fd;
@@ -10786,7 +10784,7 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog,
 	dev = dev_get_by_index(net, attr->link_create.target_ifindex);
 	if (!dev) {
 		rtnl_unlock();
-		bpf_log(log, "Invalid target_ifindex.\n");
+		NL_SET_ERR_MSG(extack, "Invalid target_ifindex.");
 		return -EINVAL;
 	}

@@ -10808,15 +10806,13 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog,
 	}

 	netdev_lock_ops(dev);
-	err = dev_xdp_attach_link(dev, &extack, link);
+	err = dev_xdp_attach_link(dev, extack, link);
 	netdev_unlock_ops(dev);
 	rtnl_unlock();

 	if (err) {
 		link->dev = NULL;
 		bpf_link_cleanup(&link_primer);
-		if (extack._msg)
-			bpf_log(log, "%s\n", extack._msg);
 		goto out_put_dev;
 	}


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