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/**
* \file pagein.c
*
* \brief Segment page-in routines.
*
* This program is free software under the GNU General Public License
* (>=v2). Read the file COPYING that comes with GRASS for details.
*
* \author GRASS GIS Development Team
*
* \date 2005-2009
*/
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <grass/gis.h>
#include "local_proto.h"
/**
* \brief Internal use only
*
* Segment pagein.
*
* Finds <b>n</b> in the segment file, <b>seg</b>, and selects it as the
* current segment.
*
* \param[in] SEG segment
* \param[in] n segment number
* \return 1 if successful
* \return -1 if unable to seek or read segment file
*/
int seg_pagein(SEGMENT *SEG, int n)
{
int cur;
int read_result;
/* is n the current segment? */
if (n == SEG->scb[SEG->cur].n)
return SEG->cur;
/* segment n is in memory ? */
if (SEG->load_idx[n] >= 0) {
cur = SEG->load_idx[n];
if (SEG->scb[cur].age != SEG->youngest) {
/* splice out */
SEG->scb[cur].age->younger->older = SEG->scb[cur].age->older;
SEG->scb[cur].age->older->younger = SEG->scb[cur].age->younger;
/* splice in */
SEG->scb[cur].age->younger = SEG->youngest->younger;
SEG->scb[cur].age->older = SEG->youngest;
SEG->scb[cur].age->older->younger = SEG->scb[cur].age;
SEG->scb[cur].age->younger->older = SEG->scb[cur].age;
/* make it youngest */
SEG->youngest = SEG->scb[cur].age;
}
return SEG->cur = cur;
}
/* find a slot to use to hold segment */
if (!SEG->nfreeslots) {
/* use oldest segment */
SEG->oldest = SEG->oldest->younger;
cur = SEG->oldest->cur;
SEG->oldest->cur = -1;
/* unload segment */
if (SEG->scb[cur].n >= 0) {
SEG->load_idx[SEG->scb[cur].n] = -1;
/* write it out if dirty */
if (SEG->scb[cur].dirty) {
if (seg_pageout(SEG, cur) < 0)
return -1;
}
}
}
else {
/* free slots left */
cur = SEG->freeslot[--SEG->nfreeslots];
}
/* read in the segment */
SEG->scb[cur].n = n;
SEG->scb[cur].dirty = 0;
SEG->seek(SEG, SEG->scb[cur].n, 0);
read_result = read(SEG->fd, SEG->scb[cur].buf, SEG->size);
if (read_result == 0) {
/* this can happen if the file was not zero-filled,
* i.e. formatted with Segment_format_nofill() or
* Segment_format() used lseek for file initialization */
G_debug(1, "Segment pagein: zero read");
memset(SEG->scb[cur].buf, 0, SEG->size);
}
else if (read_result != SEG->size) {
G_debug(2, "Segment pagein: read_result=%d SEG->size=%d", read_result,
SEG->size);
if (read_result < 0)
G_warning("Segment pagein: %s", strerror(errno));
else
G_warning("Segment pagein: short count during read(), got %d, "
"expected %d",
read_result, SEG->size);
return -1;
}
/* add loaded segment to index */
SEG->load_idx[n] = cur;
/* make it youngest segment */
SEG->youngest = SEG->youngest->younger;
SEG->scb[cur].age = SEG->youngest;
SEG->youngest->cur = cur;
return SEG->cur = cur;
}
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