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

[Leon Hwang <leon.hwang@linux.dev>]

In order to drop the dependency of bpf_verifier.h in net/core/dev.c, pass
extack to bpf_xdp_link_attach() in link_create(). Afterwards, transfer
the error message from extack to log buffer in link_create().

Drop the stub bpf_log(), because it is not used in net/core/dev.c
anymore when CONFIG_BPF_SYSCALL is not set.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
Address Jakub's review in the series
"bpf: Add syscall common attrs support for xdp link_create" [1].

Links:
[1] https://lore.kernel.org/bpf/20261020152804.39863-1-leon.hwang@linux.dev/
---
 include/linux/bpf_verifier.h |  5 -----
 include/linux/netdevice.h    |  2 +-
 kernel/bpf/syscall.c         |  8 +++++++-
 net/core/dev.c               | 10 +++-------
 4 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 1d34ece19bcc..5926f13ff43c 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 4548b0fd824d..f5d6438c4b8f 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 87cd122d1024..26917a1ecbb2 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5944,8 +5944,14 @@ 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);
+{
+		struct netlink_ext_ack extack = {};
+
+		ret = bpf_xdp_link_attach(attr, prog, &extack);
+		if (extack._msg)
+			bpf_log(log, "%s\n", extack._msg);
 		break;
+}
 	case BPF_PROG_TYPE_SCHED_CLS:
 		if (attr->link_create.attach_type == BPF_TCX_INGRESS ||
 		    attr->link_create.attach_type == BPF_TCX_EGRESS)
diff --git a/net/core/dev.c b/net/core/dev.c
index a142613536b0..d79a589206e1 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;
 	}

--
2.55.0