netfilter: nf_log: move log buffering to core logging

This patch moves Eric Dumazet's log buffer implementation from the
xt_log.h header file to the core net/netfilter/nf_log.c. This also
includes the renaming of the structure and functions to avoid possible
undesired namespace clashes.

This change allows us to use it from the arp and bridge packet logging
implementation in follow up patches.

Author: ummakynes

include/net/netfilter/nf_log.h

@@ -72,4 +72,10 @@ void nf_log_packet(struct net *net,
 		   const struct nf_loginfo *li,
 		   const char *fmt, ...);
 
+struct nf_log_buf;
+
+struct nf_log_buf *nf_log_buf_open(void);
+__printf(2, 3) int nf_log_buf_add(struct nf_log_buf *m, const char *f, ...);
+void nf_log_buf_close(struct nf_log_buf *m);
+
 #endif /* _NF_LOG_H */

include/net/netfilter/xt_log.h

@@ -157,6 +157,63 @@ void nf_log_packet(struct net *net,
 }
 EXPORT_SYMBOL(nf_log_packet);
 
+#define S_SIZE (1024 - (sizeof(unsigned int) + 1))
+
+struct nf_log_buf {
+	unsigned int	count;
+	char		buf[S_SIZE + 1];
+};
+static struct nf_log_buf emergency, *emergency_ptr = &emergency;
+
+__printf(2, 3) int nf_log_buf_add(struct nf_log_buf *m, const char *f, ...)
+{
+	va_list args;
+	int len;
+
+	if (likely(m->count < S_SIZE)) {
+		va_start(args, f);
+		len = vsnprintf(m->buf + m->count, S_SIZE - m->count, f, args);
+		va_end(args);
+		if (likely(m->count + len < S_SIZE)) {
+			m->count += len;
+			return 0;
+		}
+	}
+	m->count = S_SIZE;
+	printk_once(KERN_ERR KBUILD_MODNAME " please increase S_SIZE\n");
+	return -1;
+}
+EXPORT_SYMBOL_GPL(nf_log_buf_add);
+
+struct nf_log_buf *nf_log_buf_open(void)
+{
+	struct nf_log_buf *m = kmalloc(sizeof(*m), GFP_ATOMIC);
+
+	if (unlikely(!m)) {
+		local_bh_disable();
+		do {
+			m = xchg(&emergency_ptr, NULL);
+		} while (!m);
+	}
+	m->count = 0;
+	return m;
+}
+EXPORT_SYMBOL_GPL(nf_log_buf_open);
+
+void nf_log_buf_close(struct nf_log_buf *m)
+{
+	m->buf[m->count] = 0;
+	printk("%s\n", m->buf);
+
+	if (likely(m != &emergency))
+		kfree(m);
+	else {
+		emergency_ptr = m;
+		local_bh_enable();
+	}
+}
+EXPORT_SYMBOL_GPL(nf_log_buf_close);
+
 #ifdef CONFIG_PROC_FS
 static void *seq_start(struct seq_file *seq, loff_t *pos)
 {