bpf: tcp: seq_file: Remove bpf_seq_afinfo from tcp_iter_state

A following patch will create a separate struct to store extra
bpf_iter state and it will embed the existing tcp_iter_state like this:
struct bpf_tcp_iter_state {
struct tcp_iter_state state;
/* More bpf_iter specific states here ... */
}

As a prep work, this patch removes the
"struct tcp_seq_afinfo *bpf_seq_afinfo" where its purpose is
to tell if it is iterating from bpf_iter instead of proc fs.
Currently, if "*bpf_seq_afinfo" is not NULL, it is iterating from
bpf_iter. The kernel should not filter by the addr family and
leave this filtering decision to the bpf prog.

Instead of adding a "*bpf_seq_afinfo" pointer, this patch uses the
"seq->op == &bpf_iter_tcp_seq_ops" test to tell if it is iterating
from the bpf iter.

The bpf_iter_(init|fini)_tcp() is left here to prepare for
the change of a following patch.

Signed-off-by: Martin KaFai Lau <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Acked-by: Kuniyuki Iwashima <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

include/net/tcp.h

···
 	struct seq_net_private	p;
 	enum tcp_seq_states	state;
 	struct sock		*syn_wait_sk;
-	struct tcp_seq_afinfo	*bpf_seq_afinfo;
 	int			bucket, offset, sbucket, num;
 	loff_t			last_pos;
 };

net/ipv4/tcp_ipv4.c

···
 #endif
 static unsigned short seq_file_family(const struct seq_file *seq)
 {
-	const struct tcp_iter_state *st = seq->private;
-	const struct tcp_seq_afinfo *afinfo = st->bpf_seq_afinfo;
+	const struct tcp_seq_afinfo *afinfo;
 
+#ifdef CONFIG_BPF_SYSCALL
 	/* Iterated from bpf_iter.  Let the bpf prog to filter instead. */
-	if (afinfo)
+	if (seq->op == &bpf_iter_tcp_seq_ops)
 		return AF_UNSPEC;
+#endif
 
 	/* Iterated from proc fs */
 	afinfo = PDE_DATA(file_inode(seq->file));
···
 
 static int bpf_iter_init_tcp(void *priv_data, struct bpf_iter_aux_info *aux)
 {
-	struct tcp_iter_state *st = priv_data;
-	struct tcp_seq_afinfo *afinfo;
-	int ret;
-
-	afinfo = kmalloc(sizeof(*afinfo), GFP_USER | __GFP_NOWARN);
-	if (!afinfo)
-		return -ENOMEM;
-
-	afinfo->family = AF_UNSPEC;
-	st->bpf_seq_afinfo = afinfo;
-	ret = bpf_iter_init_seq_net(priv_data, aux);
-	if (ret)
-		kfree(afinfo);
-	return ret;
+	return bpf_iter_init_seq_net(priv_data, aux);
 }
 
 static void bpf_iter_fini_tcp(void *priv_data)
 {
-	struct tcp_iter_state *st = priv_data;
-
-	kfree(st->bpf_seq_afinfo);
 	bpf_iter_fini_seq_net(priv_data);
 }