/**
 * 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;
        mm_segment_t fs_save;
        ssize_t rc;

        lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
        if (!lower_file)
                return -EIO;
        fs_save = get_fs();
        set_fs(get_ds());
        rc = vfs_write(lower_file, data, size, &offset);
        set_fs(fs_save);
        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]\n", __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]\n", __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]\n", 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;
        mm_segment_t fs_save;
        ssize_t rc;

        lower_file = ecryptfs_inode_to_private(ecryptfs_inode)->lower_file;
        if (!lower_file)
                return -EIO;
        fs_save = get_fs();
        set_fs(get_ds());
        rc = vfs_read(lower_file, data, size, &offset);
        set_fs(fs_save);
        return rc;
}

/**
 * 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;
}