/**
   * eCryptfs: Linux filesystem encryption layer
   *
   * Copyright (C) 2007 International Business Machines Corp.
   *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License as
   * published by the Free Software Foundation; either version 2 of the
   * License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
   * 02111-1307, USA.
   */
  
  #include <linux/fs.h>
  #include <linux/pagemap.h>
  #include "ecryptfs_kernel.h"
  
  /**
   * ecryptfs_write_lower
   * @ecryptfs_inode: The eCryptfs inode
   * @data: Data to write
   * @offset: Byte offset in the lower file to which to write the data
   * @size: Number of bytes from @data to write at @offset in the lower
   *        file
   *
   * Write data to the lower file.
   *
   * Returns bytes written on success; less than zero on error
   */
  int ecryptfs_write_lower(struct inode *ecryptfs_inode, char *data,
  			 loff_t offset, size_t size)
  {
  	struct file *lower_file;
  	ssize_t rc;
  
  	lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
  	if (!lower_file)
  		return -EIO;
  	rc = kernel_write(lower_file, data, size, offset);
  	mark_inode_dirty_sync(ecryptfs_inode);
  	return rc;
  }
  
  /**
   * ecryptfs_write_lower_page_segment
   * @ecryptfs_inode: The eCryptfs inode
   * @page_for_lower: The page containing the data to be written to the
   *                  lower file
   * @offset_in_page: The offset in the @page_for_lower from which to
   *                  start writing the data
   * @size: The amount of data from @page_for_lower to write to the
   *        lower file
   *
   * Determines the byte offset in the file for the given page and
   * offset within the page, maps the page, and makes the call to write
   * the contents of @page_for_lower to the lower inode.
   *
   * Returns zero on success; non-zero otherwise
   */
  int ecryptfs_write_lower_page_segment(struct inode *ecryptfs_inode,
  				      struct page *page_for_lower,
  				      size_t offset_in_page, size_t size)
  {
  	char *virt;
  	loff_t offset;
  	int rc;
  
  	offset = ((((loff_t)page_for_lower->index) << PAGE_CACHE_SHIFT)
  		  + offset_in_page);
  	virt = kmap(page_for_lower);
  	rc = ecryptfs_write_lower(ecryptfs_inode, virt, offset, size);
  	if (rc > 0)
  		rc = 0;
  	kunmap(page_for_lower);
  	return rc;
  }
  
  /**
   * ecryptfs_write
   * @ecryptfs_inode: The eCryptfs file into which to write
   * @data: Virtual address where data to write is located
   * @offset: Offset in the eCryptfs file at which to begin writing the
   *          data from @data
   * @size: The number of bytes to write from @data
   *
   * Write an arbitrary amount of data to an arbitrary location in the
   * eCryptfs inode page cache. This is done on a page-by-page, and then
   * by an extent-by-extent, basis; individual extents are encrypted and
   * written to the lower page cache (via VFS writes). This function
   * takes care of all the address translation to locations in the lower
   * filesystem; it also handles truncate events, writing out zeros
   * where necessary.
   *
   * Returns zero on success; non-zero otherwise
   */
  int ecryptfs_write(struct inode *ecryptfs_inode, char *data, loff_t offset,
  		   size_t size)
  {
  	struct page *ecryptfs_page;
  	struct ecryptfs_crypt_stat *crypt_stat;
  	char *ecryptfs_page_virt;
  	loff_t ecryptfs_file_size = i_size_read(ecryptfs_inode);
  	loff_t data_offset = 0;
  	loff_t pos;
  	int rc = 0;
  
  	crypt_stat = &ecryptfs_inode_to_private(ecryptfs_inode)->crypt_stat;
  	/*
  	 * if we are writing beyond current size, then start pos
  	 * at the current size - we'll fill in zeros from there.
  	 */
  	if (offset > ecryptfs_file_size)
  		pos = ecryptfs_file_size;
  	else
  		pos = offset;
  	while (pos < (offset + size)) {
  		pgoff_t ecryptfs_page_idx = (pos >> PAGE_CACHE_SHIFT);
  		size_t start_offset_in_page = (pos & ~PAGE_CACHE_MASK);
  		size_t num_bytes = (PAGE_CACHE_SIZE - start_offset_in_page);
  		loff_t total_remaining_bytes = ((offset + size) - pos);
  
  		if (fatal_signal_pending(current)) {
  			rc = -EINTR;
  			break;
  		}
  
  		if (num_bytes > total_remaining_bytes)
  			num_bytes = total_remaining_bytes;
  		if (pos < offset) {
  			/* remaining zeros to write, up to destination offset */
  			loff_t total_remaining_zeros = (offset - pos);
  
  			if (num_bytes > total_remaining_zeros)
  				num_bytes = total_remaining_zeros;
  		}
  		ecryptfs_page = ecryptfs_get_locked_page(ecryptfs_inode,
  							 ecryptfs_page_idx);
  		if (IS_ERR(ecryptfs_page)) {
  			rc = PTR_ERR(ecryptfs_page);
  			printk(KERN_ERR "%s: Error getting page at "
  			       "index [%ld] from eCryptfs inode "
  			       "mapping; rc = [%d]
  ", __func__,
  			       ecryptfs_page_idx, rc);
  			goto out;
  		}
  		ecryptfs_page_virt = kmap_atomic(ecryptfs_page);
  
  		/*
  		 * pos: where we're now writing, offset: where the request was
  		 * If current pos is before request, we are filling zeros
  		 * If we are at or beyond request, we are writing the *data*
  		 * If we're in a fresh page beyond eof, zero it in either case
  		 */
  		if (pos < offset || !start_offset_in_page) {
  			/* We are extending past the previous end of the file.
  			 * Fill in zero values to the end of the page */
  			memset(((char *)ecryptfs_page_virt
  				+ start_offset_in_page), 0,
  				PAGE_CACHE_SIZE - start_offset_in_page);
  		}
  
  		/* pos >= offset, we are now writing the data request */
  		if (pos >= offset) {
  			memcpy(((char *)ecryptfs_page_virt
  				+ start_offset_in_page),
  			       (data + data_offset), num_bytes);
  			data_offset += num_bytes;
  		}
  		kunmap_atomic(ecryptfs_page_virt);
  		flush_dcache_page(ecryptfs_page);
  		SetPageUptodate(ecryptfs_page);
  		unlock_page(ecryptfs_page);
  		if (crypt_stat->flags & ECRYPTFS_ENCRYPTED)
  			rc = ecryptfs_encrypt_page(ecryptfs_page);
  		else
  			rc = ecryptfs_write_lower_page_segment(ecryptfs_inode,
  						ecryptfs_page,
  						start_offset_in_page,
  						data_offset);
  		page_cache_release(ecryptfs_page);
  		if (rc) {
  			printk(KERN_ERR "%s: Error encrypting "
  			       "page; rc = [%d]
  ", __func__, rc);
  			goto out;
  		}
  		pos += num_bytes;
  	}
  	if (pos > ecryptfs_file_size) {
  		i_size_write(ecryptfs_inode, pos);
  		if (crypt_stat->flags & ECRYPTFS_ENCRYPTED) {
  			int rc2;
  
  			rc2 = ecryptfs_write_inode_size_to_metadata(
  								ecryptfs_inode);
  			if (rc2) {
  				printk(KERN_ERR	"Problem with "
  				       "ecryptfs_write_inode_size_to_metadata; "
  				       "rc = [%d]
  ", rc2);
  				if (!rc)
  					rc = rc2;
  				goto out;
  			}
  		}
  	}
  out:
  	return rc;
  }
  
  /**
   * ecryptfs_read_lower
   * @data: The read data is stored here by this function
   * @offset: Byte offset in the lower file from which to read the data
   * @size: Number of bytes to read from @offset of the lower file and
   *        store into @data
   * @ecryptfs_inode: The eCryptfs inode
   *
   * Read @size bytes of data at byte offset @offset from the lower
   * inode into memory location @data.
   *
   * Returns bytes read on success; 0 on EOF; less than zero on error
   */
  int ecryptfs_read_lower(char *data, loff_t offset, size_t size,
  			struct inode *ecryptfs_inode)
  {
  	struct file *lower_file;
  	lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
  	if (!lower_file)
  		return -EIO;
  	return kernel_read(lower_file, offset, data, size);
  }
  
  /**
   * ecryptfs_read_lower_page_segment
   * @page_for_ecryptfs: The page into which data for eCryptfs will be
   *                     written
   * @offset_in_page: Offset in @page_for_ecryptfs from which to start
   *                  writing
   * @size: The number of bytes to write into @page_for_ecryptfs
   * @ecryptfs_inode: The eCryptfs inode
   *
   * Determines the byte offset in the file for the given page and
   * offset within the page, maps the page, and makes the call to read
   * the contents of @page_for_ecryptfs from the lower inode.
   *
   * Returns zero on success; non-zero otherwise
   */
  int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
  				     pgoff_t page_index,
  				     size_t offset_in_page, size_t size,
  				     struct inode *ecryptfs_inode)
  {
  	char *virt;
  	loff_t offset;
  	int rc;
  
  	offset = ((((loff_t)page_index) << PAGE_CACHE_SHIFT) + offset_in_page);
  	virt = kmap(page_for_ecryptfs);
  	rc = ecryptfs_read_lower(virt, offset, size, ecryptfs_inode);
  	if (rc > 0)
  		rc = 0;
  	kunmap(page_for_ecryptfs);
  	flush_dcache_page(page_for_ecryptfs);
  	return rc;
  }