/*
   * Copyright (c) 2013
   * Phillip Lougher <phillip@squashfs.org.uk>
   *
   * This work is licensed under the terms of the GNU GPL, version 2. See
   * the COPYING file in the top-level directory.
   */
  
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/pagemap.h>
  #include "page_actor.h"
  
  /*
   * This file contains implementations of page_actor for decompressing into
   * an intermediate buffer, and for decompressing directly into the
   * page cache.
   *
   * Calling code should avoid sleeping between calls to squashfs_first_page()
   * and squashfs_finish_page().
   */
  
  /* Implementation of page_actor for decompressing into intermediate buffer */
  static void *cache_first_page(struct squashfs_page_actor *actor)
  {
  	actor->next_page = 1;
  	return actor->buffer[0];
  }
  
  static void *cache_next_page(struct squashfs_page_actor *actor)
  {
  	if (actor->next_page == actor->pages)
  		return NULL;
  
  	return actor->buffer[actor->next_page++];
  }
  
  static void cache_finish_page(struct squashfs_page_actor *actor)
  {
  	/* empty */
  }
  
  struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
  	int pages, int length)
  {
  	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
  
  	if (actor == NULL)
  		return NULL;
  
  	actor->length = length ? : pages * PAGE_CACHE_SIZE;
  	actor->buffer = buffer;
  	actor->pages = pages;
  	actor->next_page = 0;
  	actor->squashfs_first_page = cache_first_page;
  	actor->squashfs_next_page = cache_next_page;
  	actor->squashfs_finish_page = cache_finish_page;
  	return actor;
  }
  
  /* Implementation of page_actor for decompressing directly into page cache. */
  static void *direct_first_page(struct squashfs_page_actor *actor)
  {
  	actor->next_page = 1;
  	return actor->pageaddr = kmap_atomic(actor->page[0]);
  }
  
  static void *direct_next_page(struct squashfs_page_actor *actor)
  {
  	if (actor->pageaddr)
  		kunmap_atomic(actor->pageaddr);
  
  	return actor->pageaddr = actor->next_page == actor->pages ? NULL :
  		kmap_atomic(actor->page[actor->next_page++]);
  }
  
  static void direct_finish_page(struct squashfs_page_actor *actor)
  {
  	if (actor->pageaddr)
  		kunmap_atomic(actor->pageaddr);
  }
  
  struct squashfs_page_actor *squashfs_page_actor_init_special(struct page **page,
  	int pages, int length)
  {
  	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
  
  	if (actor == NULL)
  		return NULL;
  
  	actor->length = length ? : pages * PAGE_CACHE_SIZE;
  	actor->page = page;
  	actor->pages = pages;
  	actor->next_page = 0;
  	actor->pageaddr = NULL;
  	actor->squashfs_first_page = direct_first_page;
  	actor->squashfs_next_page = direct_next_page;
  	actor->squashfs_finish_page = direct_finish_page;
  	return actor;
  }