uninitialized b in ide_intr()

[yanjun-wen]

void ide_intr() {
   struct buf *b;
   acquire(&ide_lock);
   if (!(b->flags & B_DIRTY) && ide_wait_ready(1) >= 0)
      insl(0x1f0, b->data, 512/4); // if READ: get data
   b->flags |= B_VALID;
   b->flags &= ˜B_DIRTY;
   wakeup(b); // wake waiting process
   if ((ide_queue = b->qnext) != 0) // start next request
      ide_start_request(ide_queue); // (if one exists)
   release(&ide_lock);
}

should be:

void ide_intr() {
   struct buf *b = ide_queue;  // THIS LINE MODIFIED
   acquire(&ide_lock);
   if (!(b->flags & B_DIRTY) && ide_wait_ready(1) >= 0)
      insl(0x1f0, b->data, 512/4); // if READ: get data
   b->flags |= B_VALID;
   b->flags &= ˜B_DIRTY;
   wakeup(b); // wake waiting process
   if ((ide_queue = b->qnext) != 0) // start next request
      ide_start_request(ide_queue); // (if one exists)
   release(&ide_lock);
}