1 files changed, 61 insertions, 41 deletions

diff --git a/kernel/fs/buffer.c b/kernel/fs/buffer.c
index 7405738..99c3161 100644
--- a/kernel/fs/buffer.c
+++ b/kernel/fs/buffer.c
@@ -1,16 +1,76 @@
+#include <asm/interrupt.h>
+#include <errno.h>
 #include <kernel/con.h>
 #include <kernel/fs.h>
 #include <stdint.h>
 #include <string.h>
 
 /* memory dedicated to the block cache */
+/* TODO: start buffers at kernel end not 512K */
 #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);
+struct buffer *buffer_get_block(uint16_t device, uint16_t block) {
+  struct buffer **p = &mru;
+  struct buffer *b;
+
+  if(!device)
+    return NULL;
+
+  /* check if the requested block is already in the cache */
+  while(b = *p) {
+    if(b->b_device != device || b->b_block != block)
+      goto next;
+    /* remove the buffer from the list */
+    if(lru == b && b->b_next)   lru = b->b_next;
+    if(b->b_next)               b->b_next->b_prev = b->b_prev;
+    if(b->b_prev)               b->b_prev->b_next = b->b_next;
+    /* put the buffer back at the MRU end of the list */
+    b->b_next = NULL;
+    b->b_prev = mru;
+    if(mru != b)
+      mru->b_next = b;
+    mru = b;
+    cli();
+    /* if the buffer exists but isn't populated. wait on it */
+    if(!b->b_present) {
+      sleep_on(&b->b_wait);
+      printk("[buf] Waiting for buffer %04x:%04x to be populated...\n", b->b_device, b->b_block);
+    }
+    sti();
+    printk("[buf] Fetched block %04x:%04x from cache\n", b->b_device, b->b_block);
+    return b->b_device ? b : NULL;
+next:
+    p = &b->b_prev;
+  }
+
+  /*
+   * otherwise, iterate through the least recently used
+   * buffers, to find a buffer that isn't pending an
+   * I/O operation, and read into it.
+   */
+
+  p = &lru;
+  while(b = *p) {
+    if(b->b_present || !b->b_device)
+      break;
+    p = &(*p)->b_next;
+  }
+
+  if(!b)
+    return NULL;
+
+  b->b_device = device;
+  b->b_block = block;
+  b->b_present = 0;
+  block_read(b);
+  wake_up(&b->b_wait);
+  printk("[buf] Called driver to read block %04x:%04x\n", b->b_device, b->b_block);
+  return b->b_device ? b : NULL;
+}
 
 void buffer_init(void) {
   int c = 0;
@@ -40,43 +100,3 @@ void buffer_init(void) {
 
   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;
-}