The first version of v0.1

1 files changed, 97 insertions, 0 deletions

diff --git a/cache.c b/cache.c
new file mode 100644
index 0000000..bfcdf29
--- /dev/null
+++ b/cache.c
@@ -0,0 +1,97 @@
+#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;
+}