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