/*
   * 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/fs.h>
  #include <linux/vfs.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/string.h>
  #include <linux/pagemap.h>
  #include <linux/mutex.h>
  
  #include "squashfs_fs.h"
  #include "squashfs_fs_sb.h"
  #include "squashfs_fs_i.h"
  #include "squashfs.h"
  #include "page_actor.h"
  
  static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
  	int pages, struct page **page);
  
  /* Read separately compressed datablock directly into page cache */
  int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
  
  {
  	struct inode *inode = target_page->mapping->host;
  	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
  
  	int file_end = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
  	int mask = (1 << (msblk->block_log - PAGE_CACHE_SHIFT)) - 1;
  	int start_index = target_page->index & ~mask;
  	int end_index = start_index | mask;
  	int i, n, pages, missing_pages, bytes, res = -ENOMEM;
  	struct page **page;
  	struct squashfs_page_actor *actor;
  	void *pageaddr;
  
  	if (end_index > file_end)
  		end_index = file_end;
  
  	pages = end_index - start_index + 1;
  
  	page = kmalloc(sizeof(void *) * pages, GFP_KERNEL);
  	if (page == NULL)
  		return res;
  
  	/*
  	 * Create a "page actor" which will kmap and kunmap the
  	 * page cache pages appropriately within the decompressor
  	 */
  	actor = squashfs_page_actor_init_special(page, pages, 0);
  	if (actor == NULL)
  		goto out;
  
  	/* Try to grab all the pages covered by the Squashfs block */
  	for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
  		page[i] = (n == target_page->index) ? target_page :
  			grab_cache_page_nowait(target_page->mapping, n);
  
  		if (page[i] == NULL) {
  			missing_pages++;
  			continue;
  		}
  
  		if (PageUptodate(page[i])) {
  			unlock_page(page[i]);
  			page_cache_release(page[i]);
  			page[i] = NULL;
  			missing_pages++;
  		}
  	}
  
  	if (missing_pages) {
  		/*
  		 * Couldn't get one or more pages, this page has either
  		 * been VM reclaimed, but others are still in the page cache
  		 * and uptodate, or we're racing with another thread in
  		 * squashfs_readpage also trying to grab them.  Fall back to
  		 * using an intermediate buffer.
  		 */
  		res = squashfs_read_cache(target_page, block, bsize, pages,
  								page);
  		if (res < 0)
  			goto mark_errored;
  
  		goto out;
  	}
  
  	/* Decompress directly into the page cache buffers */
  	res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
  	if (res < 0)
  		goto mark_errored;
  
  	/* Last page may have trailing bytes not filled */
  	bytes = res % PAGE_CACHE_SIZE;
  	if (bytes) {
  		pageaddr = kmap_atomic(page[pages - 1]);
  		memset(pageaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);
  		kunmap_atomic(pageaddr);
  	}
  
  	/* Mark pages as uptodate, unlock and release */
  	for (i = 0; i < pages; i++) {
  		flush_dcache_page(page[i]);
  		SetPageUptodate(page[i]);
  		unlock_page(page[i]);
  		if (page[i] != target_page)
  			page_cache_release(page[i]);
  	}
  
  	kfree(actor);
  	kfree(page);
  
  	return 0;
  
  mark_errored:
  	/* Decompression failed, mark pages as errored.  Target_page is
  	 * dealt with by the caller
  	 */
  	for (i = 0; i < pages; i++) {
  		if (page[i] == NULL || page[i] == target_page)
  			continue;
  		flush_dcache_page(page[i]);
  		SetPageError(page[i]);
  		unlock_page(page[i]);
  		page_cache_release(page[i]);
  	}
  
  out:
  	kfree(actor);
  	kfree(page);
  	return res;
  }
  
  
  static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
  	int pages, struct page **page)
  {
  	struct inode *i = target_page->mapping->host;
  	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
  						 block, bsize);
  	int bytes = buffer->length, res = buffer->error, n, offset = 0;
  	void *pageaddr;
  
  	if (res) {
  		ERROR("Unable to read page, block %llx, size %x
  ", block,
  			bsize);
  		goto out;
  	}
  
  	for (n = 0; n < pages && bytes > 0; n++,
  			bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
  		int avail = min_t(int, bytes, PAGE_CACHE_SIZE);
  
  		if (page[n] == NULL)
  			continue;
  
  		pageaddr = kmap_atomic(page[n]);
  		squashfs_copy_data(pageaddr, buffer, offset, avail);
  		memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
  		kunmap_atomic(pageaddr);
  		flush_dcache_page(page[n]);
  		SetPageUptodate(page[n]);
  		unlock_page(page[n]);
  		if (page[n] != target_page)
  			page_cache_release(page[n]);
  	}
  
  out:
  	squashfs_cache_put(buffer);
  	return res;
  }