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#include "cache.h"
#include <stdio.h>
#include <malloc.h>
/*
* Each CachePtr contains:
* - Block pointer
* - LRU previous pointer
* - LRU next pointer
* - Block data buffer address
* The first entry is the head node of the list
*/
struct cache_struct cache[CACHE_ENTRIES + 1] = {0,};
/**
* cache_init:
*
* Initialize the cache data structres.
*
*/
void cache_init(void)
{
struct cache_struct *prev, *cur;
int i;
cur = cache;
prev = &cache[CACHE_ENTRIES];
for ( i = 0; i < CACHE_ENTRIES + 1; i++ ) {
cur->sector = 0;
cur->prev = prev;
prev->next = cur;
cur->data = NULL;
prev = cur;
cur = &cache[i+1];
}
}
/**
* get_cache_sector:
*
* Check for a particular SECTOR in the sector cache,
* and if it is already there, just do nothing and return;
* otherwise load it and updata the relative cache
* structre with data pointer.
*
* @param: sector, the sector number we want check.
* @retrun: return the most recent cache structure pointer
*
*/
struct cache_struct * get_cache_sector(int sector)
{
struct cache_struct *cs = &cache[1];
struct cache_struct *head, *last;
int i;
for ( i = 0; i < CACHE_ENTRIES; i ++ ) {
if ( cs->sector == sector )
goto hit;
else
cs = &cache[i + 1];
}
/* we missed it here, so we need to load it */
miss:
/* free the first cache's buffer first */
if ( cache[0].next->data)
free(cache[0].next->data);
/* store it at head of real cache */
cs = cache[0].next;
cs->sector = sector;
cs->data = (void*)getonesec(sector);
hit:
/* remove cs from current position in list */
cs->prev->next = cs->next;
cs->next->prev = cs->prev;
/* add to just before head node */
last = cache[0].prev;
head = cache;
last->next = cs;
cs->prev = last;
head->prev = cs;
cs->next = head;
return cs;
}
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