LRU disk cache replacement

cd93074e · rtm · 22bac2cb · cd93074e · cd93074e · cd93074e
--- a/Notes
+++ b/Notes
@@ -357,3 +357,11 @@ OH! recursive interrupts will use up any amount of cpu[].stack!
 better buffer cache replacement
 read/write of open file that's been unlinked
+disk scheduling
+mkdir
+more than one directory content block
+sh arguments
+sh redirection
+indirect blocks
+two bugs in unlink
+how come unlink xxx fails? iput problem?
--- a/bio.c
+++ b/bio.c
@@ -10,27 +10,41 @@
 struct buf buf[NBUF];
 struct spinlock buf_table_lock;
+// linked list of all buffers, through prev/next.
+// bufhead->next is most recently used.
+// bufhead->tail is least recently used.
+struct buf bufhead;
 void
 binit(void)
 {
+  struct buf *b;
  initlock(&buf_table_lock, "buf_table");
+  bufhead.prev = &bufhead;
+  bufhead.next = &bufhead;
+  for(b = buf; b < buf+NBUF; b++){
+    b->next = bufhead.next;
+    b->prev = &bufhead;
+    bufhead.next->prev = b;
+    bufhead.next = b;
+  }
 }
 struct buf *
 getblk(uint dev, uint sector)
 {
  struct buf *b;
-  static struct buf *scan = buf;
-  int i;
  acquire(&buf_table_lock);
  while(1){
-    for(b = buf; b < buf+NBUF; b++)
+    for(b = bufhead.next; b != &bufhead; b = b->next)
      if((b->flags & (B_BUSY|B_VALID)) && b->dev == dev && b->sector == sector)
        break;
-    if(b < buf+NBUF){
+    if(b != &bufhead){
      if(b->flags & B_BUSY){
        sleep(buf, &buf_table_lock);
      } else {
@@ -39,10 +53,7 @@ getblk(uint dev, uint sector)
        return b;
      }
    } else {
-      for(i = 0; i < NBUF; i++){
+      for(b = bufhead.prev; b != &bufhead; b = b->prev){
-        b = scan++;
-        if(scan >= buf+NBUF)
-          scan = buf;
        if((b->flags & B_BUSY) == 0){
          b->flags = B_BUSY;
          b->dev = dev;
@@ -64,8 +75,9 @@ bread(uint dev, uint sector)
  extern struct spinlock ide_lock;
  b = getblk(dev, sector);
-  if(b->flags & B_VALID)
+  if(b->flags & B_VALID){
    return b;
+  }
  acquire(&ide_lock);
  c = ide_start_rw(dev & 0xff, sector, b->data, 1, 1);
@@ -99,6 +111,13 @@ brelse(struct buf *b)
  acquire(&buf_table_lock);
+  b->next->prev = b->prev;
+  b->prev->next = b->next;
+  b->next = bufhead.next;
+  b->prev = &bufhead;
+  bufhead.next->prev = b;
+  bufhead.next = b;
  b->flags &= ~B_BUSY;
  wakeup(buf);

--- a/buf.h
+++ b/buf.h
@@ -2,6 +2,8 @@ struct buf {
  int flags;
  uint dev;
  uint sector;
+  struct buf *prev;
+  struct buf *next;
  uchar data[512];
 };
 #define B_BUSY 0x1

--- a/fs.c
+++ b/fs.c
@@ -505,7 +505,7 @@ unlink(char *cp)
  if ((ip = namei(cp, &pinum)) == 0) {
-    cprintf("file to be unlinked doesn't exist\n");
+    cprintf("unlink(%s) it doesn't exist\n", cp);
    return -1;
  }

--- a/usertests.c
+++ b/usertests.c
@@ -303,7 +303,7 @@ createdelete()
 void
 unlinkread()
 {
-  int fd;
+  int fd, fd1;
  fd = open("unlinkread", O_CREATE | O_RDWR);
  if(fd < 0){
@@ -322,15 +322,25 @@ unlinkread()
    puts("unlink unlinkread failed\n");
    exit();
  }
+  fd1 = open("xxx", O_CREATE | O_RDWR);
+  write(fd1, "yyy", 3);
+  close(fd1);
  if(read(fd, buf, sizeof(buf)) != 5){
    puts("unlinkread read failed");
    exit();
  }
+  if(buf[0] != 'h'){
+    puts("unlinkread wrong data\n");
+    exit();
+  }
  if(write(fd, buf, 10) != 10){
    puts("unlinkread write failed\n");
    exit();
  }
  close(fd);
+  unlink("xxx");
  puts("unlinkread ok\n");
 }
@@ -339,7 +349,7 @@ main(int argc, char *argv[])
 {
  puts("usertests starting\n");
-  //unlinkread();
+  unlinkread();
  createdelete();
  twofiles();
  sharedfd();