V5/usr/sys/file.h

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including files from this version of Unix. 
struct file {
	char	f_flag;
	char	f_count;
	int	f_inode;
	char	*f_offset[2];
} file[NFILE];

/* flags */
#define	FREAD	01
#define	FWRITE	02
#define	FPIPE	04