1 files changed, 82 insertions, 0 deletions
diff --git a/kernel/fs/buffer.c b/kernel/fs/buffer.c
new file mode 100644
index 0000000..7405738
--- /dev/null
+++ b/kernel/fs/buffer.c
@@ -0,0 +1,82 @@
+#include <kernel/con.h>
+#include <kernel/fs.h>
+#include <stdint.h>
+#include <string.h>
+
+/* memory dedicated to the block cache */
+#define BSTART 0x80000
+#define BEND 0xA0000
+
+static struct buffer *lru;
+static struct buffer *mru;
+
+struct buffer *buffer_get_block(uint16_t device, uint16_t block);
+
+void buffer_init(void) {
+  int c = 0;
+  struct buffer *last = NULL;
+  struct buffer *b = (struct buffer*) BSTART;
+  void *d = (void*) (BEND - BLOCK_SIZE);
+
+  while(d > (void*) b) {
+    memset(b, 0, sizeof(struct buffer));
+
+    b->b_data = d;
+    b->b_prev = last;
+
+    if(last)
+      last->b_next = b;
+
+    last = b;
+
+    b = (struct buffer*) ((void*) b + sizeof(struct buffer));
+    d = (void*) (d - (void*) BLOCK_SIZE);
+
+    c++;
+  }
+
+  lru = (struct buffer*) BSTART;
+  mru = last;
+
+  printk("[buf] Buffers initialized (0x%x buffers in pool)\n", c);
+}
+
+struct buffer *buffer_get_block(uint16_t device, uint16_t block) {
+  int ret;
+  struct buffer **p = &mru;
+  struct buffer *b;
+
+  /* check if the requested block is already in the cache */
+  while(*p) {
+    if((*p)->b_device == device && (*p)->b_block == block) {
+      /* put the buffer back at the MRU end of the list */
+      (*p)->b_next = NULL;
+      (*p)->b_prev = mru;
+      mru = *p;
+      return *p;
+    }
+    p = &(*p)->b_prev;
+  }
+
+  /* find a buffer at the end of the LRU list */
+  b = lru;
+  lru = lru->b_next;
+  lru->b_prev = NULL;
+  ret = block_read(b->b_data, block);
+  /* abort if we failed to read in the block */
+  if(ret < 0) {
+    /* release the allocated buffer to the pool */
+    lru->b_prev = b;
+    b->b_next = lru;
+    b->b_prev = NULL;
+    lru = b;
+    return NULL;
+  }
+  b->b_device = device;
+  b->b_block = block;
+  /* put the buffer back at the MRU end of the list */
+  b->b_next = NULL;
+  b->b_prev = mru;
+  mru = b;
+  return b;
+}