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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 2005-2006
*/
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <grass/segment.h>
static int segment_select(SEGMENT *, int);
/**
* \fn int segment_pagein (SEGMENT *SEG, int n)
*
* \brief 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 segment_pagein(SEGMENT * SEG, int n)
{
int age;
int cur;
int i;
int read_result;
/* is n the current segment? */
if (n == SEG->scb[SEG->cur].n)
return SEG->cur;
/* search the in memory segments */
for (i = 0; i < SEG->nseg; i++)
if (n == SEG->scb[i].n)
return segment_select(SEG, i);
/* find a slot to use to hold segment */
age = 0;
cur = 0;
for (i = 0; i < SEG->nseg; i++)
if (SEG->scb[i].n < 0) { /* free slot */
cur = i;
break;
}
else if (age < SEG->scb[i].age) { /* find oldest segment */
cur = i;
age = SEG->scb[i].age;
}
/* if slot is used, write it out, if dirty */
if (SEG->scb[cur].n >= 0 && SEG->scb[cur].dirty)
if (segment_pageout(SEG, cur) < 0)
return -1;
/* read in the segment */
SEG->scb[cur].n = n;
SEG->scb[cur].dirty = 0;
segment_seek(SEG, SEG->scb[cur].n, 0);
read_result = read(SEG->fd, SEG->scb[cur].buf, SEG->size);
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 if (read_result == 0)
G_warning("segment_pagein: read EOF");
else
G_warning
("segment_pagein: short count during read(), got %d, expected %d",
read_result, SEG->size);
return -1;
}
return segment_select(SEG, cur);
}
static int segment_select(SEGMENT * SEG, int n)
{
int i;
SEG->scb[n].age = 0;
for (i = 0; i < SEG->nseg; i++)
SEG->scb[i].age++;
return SEG->cur = n;
}
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