int rfio_preseek (int s, const struct iovec *iov, int iovnb);
Under Linux, for large files:
#define _LARGEFILE64_SOURCE
#include <sys/types.h>
#include "rfio_api.h"
int rfio_preseek64 (int s, const struct iovec64 *iov, int iovnb);
For large files, under other systems:
#include <sys/types.h>
#include "rfio_api.h"
int rfio_preseek64 (int s, const struct iovec64 *iov, int iovnb);
rfio_preseek64 does the prefetch for large files, using an array of structures of type iovec64 rather than an array of iovec.
RFIO_READOPT must be set to RFIO_READBUF, which is the default. The default internal buffer size is 128 kB, but the buffer size can be set with an entry RFIO IOBUFSIZE in shift.conf. Then rfio_read gets the data from that buffer.
/* tpreseek - write NBRECORDS_TOWRITE records and
read back NBRECORDS_TOREAD using the rfio_preseek function */
#include <fcntl.h>
#include <stdio.h>
#if defined(_WIN32)
#include <winsock2.h>
#endif
#include "rfio_api.h"
#define NBRECORDS_TOREAD 5
#define NBRECORDS_TOWRITE 10
main(argc, argv)
int argc;
char **argv;
{
char buf[65536];
int errflg = 0;
int fd;
int i;
struct iovec iov[NBRECORDS_TOREAD];
int iovnb = NBRECORDS_TOREAD;
int j;
static int lengths[NBRECORDS_TOWRITE] = {4096, 32768, 16384, 8192,
65536, 32768, 16384, 4096, 65536, 8192};
static int records_toread[NBRECORDS_TOREAD] = {2, 4, 5, 8, 9};
#if defined(_WIN32)
WSADATA wsadata;
#endif
if (argc != 2) {
fprintf (stderr, "usage: tpreseek pathname\n");
exit (1);
}
#if defined(_WIN32)
if (WSAStartup (MAKEWORD (2, 0), &wsadata)) {
fprintf (stderr, "WSAStartup unsuccessful\n");
exit (2);
}
#endif
while (! errflg) {
/* Write variable length records.
* Each record is filled with the record index
*/
if ((fd = rfio_open (argv[1],
O_WRONLY|O_CREAT|O_TRUNC, 0644)) < 0) {
rfio_perror ("rfio_open");
errflg++;
break;
}
for (j = 0; j < NBRECORDS_TOWRITE; j++) {
for (i = 0; i < lengths[j]; i++)
buf[i] = j;
if (rfio_write (fd, buf, lengths[j]) < 0) {
rfio_perror ("rfio_write");
errflg++;
break;
}
}
(void)rfio_close (fd);
if (errflg) break;
/* Prefetch a few records: the actual offsets and lengths
* of the records is set in the array of iov structures
*/
if ((fd = rfio_open (argv[1], O_RDONLY)) < 0) {
rfio_perror ("rfio_open");
errflg++;
break;
}
for (j = 0; j < NBRECORDS_TOREAD; j++) {
/* compute record offset */
iov[j].iov_base = 0;
for (i = 0; i < records_toread[j]; i++)
iov[j].iov_base = (char *) iov[j].iov_base +
lengths[i];
/* set length */
iov[j].iov_len = lengths[records_toread[j]];
}
if (rfio_preseek (fd, iov, iovnb) < 0) {
rfio_perror ("rfio_preseek");
errflg++;
break;
}
/* Read back the records and check their cpntents */
for (j = 0; j < NBRECORDS_TOREAD; j++) {
if (rfio_lseek (fd, (off_t) iov[j].iov_base,
SEEK_SET) < 0) {
rfio_perror ("rfio_lseek");
errflg++;
break;
}
if (rfio_read (fd, buf, iov[j].iov_len) < 0) {
rfio_perror ("rfio_read");
errflg++;
break;
}
for (i = 0; i < iov[j].iov_len; i++) {
if (buf[i] != records_toread[j]) {
fprintf (stderr,
"incorrect data read, record %d\n",
records_toread[j]);
errflg++;
break;
}
}
if (errflg) break;
}
(void) rfio_close (fd);
break;
}
if (rfio_unlink (argv[1]) < 0) {
rfio_perror ("rfio_unlink");
errflg++;
}
#if defined(_WIN32)
WSACleanup();
#endif
exit (errflg ? 1 : 0);
}