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The C and C++ Include Header Files

cat -n /usr/include/linux/netfilter_ipv4/ipt_LOG.h

     1	/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
     2	#ifndef _IPT_LOG_H
     3	#define _IPT_LOG_H
     4	
     5	/* make sure not to change this without changing netfilter.h:NF_LOG_* (!) */
     6	#define IPT_LOG_TCPSEQ		0x01	/* Log TCP sequence numbers */
     7	#define IPT_LOG_TCPOPT		0x02	/* Log TCP options */
     8	#define IPT_LOG_IPOPT		0x04	/* Log IP options */
     9	#define IPT_LOG_UID		0x08	/* Log UID owning local socket */
    10	#define IPT_LOG_NFLOG		0x10	/* Unsupported, don't reuse */
    11	#define IPT_LOG_MACDECODE	0x20	/* Decode MAC header */
    12	#define IPT_LOG_MASK		0x2f
    13	
    14	struct ipt_log_info {
    15		unsigned char level;
    16		unsigned char logflags;
    17		char prefix[30];
    18	};
    19	
    20	#endif /*_IPT_LOG_H*/