#

/* Additional system calls added to vanilla V6 Unix.
 */

#include "../param.h"
#include "../systm.h"
#include "../user.h"
#include "../reg.h"
#include "../file.h"
#include "../inode.h"


/*
 * lseek system call
 */

lseek()
{
	int n[2];
	register *fp, t;

	fp = getf(u.u_ar0[R0]);
	if(fp == NULL)
		return;
	if(fp->f_flag&FPIPE) {
		u.u_error = ESPIPE;
		return;
	}
	t = u.u_arg[2];
	n[0] = u.u_arg[0];
	n[1] = u.u_arg[1];
	switch(t) {

	case 0:	 /* absolute */
		break;
	case 1:	 /* relative */
		n[0] =+ fp->f_offset[0];
		dpadd(n, fp->f_offset[1]);
		break;

	case 2:	 /* to end of the file */
		n[0] =+ fp->f_inode->i_size0&0377;
		dpadd(n, fp->f_inode->i_size1);
		break;
	default:
		u.u_error = EFAULT;

	}
	u.u_ar0[R0] = fp->f_offset[0];	/* returned results in r0, r1 */
	u.u_ar0[R1] = fp->f_offset[1];
	fp->f_offset[1] = n[1];
	fp->f_offset[0] = n[0];
}