NAME
rfio_preseek - prefetch chunks of data from a file
SYNOPSIS
#include <sys/types.h>
#include "rfio_api.h"
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);
DESCRIPTION
rfio_preseek prefetches chunks of data at given offsets into an
internal buffer (on the client side), using the descriptor s generated
by a previous rfio_open. The actual offset values and the lengths are
given in the array of structures iov. The number of chunks is
specified by 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.
EXAMPLES
/* 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);
}
RETURN VALUE
This routine returns 0 if the operation was successful or -1 if the
operation failed. In the latter case, serrno is set appropriately.
ERRORS
EBADF s is not a valid descriptor.
EINVAL RFIO_READOPT is not set to RFIO_READBUF.
SENOSHOST Host unknown.
SENOSSERV Service unknown.
SETIMEDOUT Timed out.
SEBADVERSION Version ID mismatch.
SECONNDROP Connection closed by remote end.
SECOMERR Communication error.
SENORCODE Host did not return error number.
SEE ALSO
rfio_lseek(3), rfio_open(3), rfio_read(3)
AUTHOR
LCG Grid Deployment Team