/*
Questo programma e' solo un esempio dal quale
prendere qualche spunto per il timing
delle system call lseek/read.

Manca tutta la gestione degli errori,
la stima dell'overhead della gettimeofday ed
altro ancora.
*/

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/time.h>

/* resources not allocated yet */
int fd_in = -1;
long *t2_t1 = NULL ,*t3_t2 = NULL;

void myexit(int);
long deltausecs(struct timeval *,struct timeval *);

int main(int argc,char *argv[])
{
	char string[256];
	long i,numlet;
	off_t offset = 0,position;
	struct timeval t1,t2,t3;
	char buffer[1];

	if (argc != 4) {
		fprintf(stderr,"Uso: %s <dist. tra le lett.> <num. di lett.> <file da leggere>\n",argv[0]);
		myexit(5);
	}

	sscanf(argv[1],"%ld",&offset);
	sscanf(argv[2],"%ld",&numlet);

	t2_t1 = calloc(numlet, sizeof(long));
	t3_t2 = calloc(numlet, sizeof(long));

	printf("offset %ld numlet %ld\n",offset,numlet);

	if ( (fd_in = open(argv[3], O_RDONLY )) < 0 ) {
		sprintf(string,"Apertura di %1.200s fallita",argv[2]);
		perror(string); myexit(5);
	}

	position = lseek(fd_in,0L	 ,SEEK_SET);
	read(fd_in, buffer , sizeof(buffer));

	for(i = 0 ; i < numlet ; i++) {

		(void) gettimeofday( &t1 , (struct timezone *) 0);
		position = lseek(fd_in,offset,SEEK_CUR);
		(void) gettimeofday( &t2 , (struct timezone *) 0);
		read(fd_in, buffer , sizeof(buffer));
		(void) gettimeofday( &t3 , (struct timezone *) 0);

		t2_t1[i]	  = deltausecs( &t2 , &t1 );
		t3_t2[i]	  = deltausecs( &t3 , &t2 );

	}
	for(i = 0 ; i < numlet ; i++) {
		printf("Elapsed Time: lseek %-3ld read %-3ld\n",t2_t1[i],t3_t2[i]);
	}
	myexit(0);
}






long deltausecs(struct timeval *last,struct timeval *first)
{
	return (last->tv_sec - first->tv_sec) * 1000000L +
			  last->tv_usec - first->tv_usec;
}


/* free the (eventually) allocated resources */
void myexit(int ret)
{
	if (fd_in  >= 0) close(fd_in);
	if (t2_t1  != 0) free(t2_t1);
	if (t3_t2  != 0) free(t3_t2);
	exit(ret);
}