Added swap for Lab4.

src/vm/swap.c

+#include "vm/swap.h"
+#include "bitmap.h"
+#include "threads/synch.h"
+#include "threads/vaddr.h"
+#include "devices/block.h"
+
+static struct block *swap_partition; // this might not need to be saved here
+static struct bitmap *swap_freemap;
+static struct lock swap_lock;
+
+#define SECTORS_PER_PAGE (PGSIZE/BLOCK_SECTOR_SIZE)
+
+/* this must be called at the right time */
+void swap_init() {
+  block_print_stats();  
+  swap_partition = block_get_role(BLOCK_SWAP);
+  if(swap_partition) {
+    unsigned npgswp = block_size(swap_partition)/SECTORS_PER_PAGE;
+    printf("Swap size is %d pages.\n",npgswp); 
+    swap_freemap = bitmap_create(npgswp);
+    bitmap_set_all(swap_freemap, true);
+  }
+  lock_init(&swap_lock);
+}
+
+/* returns the index of the swap page storing the given memory page */
+size_t swap_out(const void* kpage) {
+  size_t index = BITMAP_ERROR;
+  lock_acquire(&swap_lock);
+  index = bitmap_scan_and_flip(swap_freemap, 0, 1, true);
+  if(index != BITMAP_ERROR) {
+    block_sector_t swap_offset = index*SECTORS_PER_PAGE;
+    for(block_sector_t i=0;i<SECTORS_PER_PAGE;i++) {
+//      printf("swap out %p to %d\n", kpage+i*BLOCK_SECTOR_SIZE, swap_offset+i);
+      block_write(swap_partition, swap_offset+i, kpage+i*BLOCK_SECTOR_SIZE);
+    }
+  }
+  lock_release(&swap_lock);
+  return index;
+}
+
+bool swap_in(size_t page_index, void* kpage) {
+  bool ok = false;
+  lock_acquire(&swap_lock);
+  if(bitmap_contains(swap_freemap, page_index, 1, false)) {
+    /* the swap page contains something (not free) */
+    block_sector_t swap_offset = page_index*SECTORS_PER_PAGE;
+    for(block_sector_t i=0;i<SECTORS_PER_PAGE;i++) {
+//      printf("swap in %d to %p\n", swap_offset+i, kpage+i*BLOCK_SECTOR_SIZE);
+      block_read(swap_partition, swap_offset+i, kpage+i*BLOCK_SECTOR_SIZE);
+    }
+    ok = true;
+  }
+  lock_release(&swap_lock);
+  return ok;
+}
+
+void swap_free(size_t page_index) {
+//  lock_acquire(&swap_lock);
+  bitmap_mark(swap_freemap, page_index); // this is already atomic
+//  lock_release(&swap_lock);
+}
+
+void swap_destroy() {
+  ASSERT(swap_freemap);
+  bitmap_destroy(swap_freemap);
+}