/*
   *  linux/fs/9p/vfs_addr.c
   *
   * This file contians vfs address (mmap) ops for 9P2000.
   *
   *  Copyright (C) 2005 by Eric Van Hensbergen <ericvh@gmail.com>
   *  Copyright (C) 2002 by Ron Minnich <rminnich@lanl.gov>
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License version 2
   *  as published by the Free Software Foundation.
   *
   *  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:
   *  Free Software Foundation
   *  51 Franklin Street, Fifth Floor
   *  Boston, MA  02111-1301  USA
   *
   */
  
  #include <linux/module.h>
  #include <linux/errno.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/stat.h>
  #include <linux/string.h>
  #include <linux/inet.h>
  #include <linux/pagemap.h>
  #include <linux/idr.h>
  #include <linux/sched.h>
  #include <linux/aio.h>
  #include <net/9p/9p.h>
  #include <net/9p/client.h>
  
  #include "v9fs.h"
  #include "v9fs_vfs.h"
  #include "cache.h"
  #include "fid.h"
  
  /**
   * v9fs_fid_readpage - read an entire page in from 9P
   *
   * @fid: fid being read
   * @page: structure to page
   *
   */
  static int v9fs_fid_readpage(struct p9_fid *fid, struct page *page)
  {
  	int retval;
  	loff_t offset;
  	char *buffer;
  	struct inode *inode;
  
  	inode = page->mapping->host;
  	p9_debug(P9_DEBUG_VFS, "
  ");
  
  	BUG_ON(!PageLocked(page));
  
  	retval = v9fs_readpage_from_fscache(inode, page);
  	if (retval == 0)
  		return retval;
  
  	buffer = kmap(page);
  	offset = page_offset(page);
  
  	retval = v9fs_fid_readn(fid, buffer, NULL, PAGE_CACHE_SIZE, offset);
  	if (retval < 0) {
  		v9fs_uncache_page(inode, page);
  		goto done;
  	}
  
  	memset(buffer + retval, 0, PAGE_CACHE_SIZE - retval);
  	flush_dcache_page(page);
  	SetPageUptodate(page);
  
  	v9fs_readpage_to_fscache(inode, page);
  	retval = 0;
  
  done:
  	kunmap(page);
  	unlock_page(page);
  	return retval;
  }
  
  /**
   * v9fs_vfs_readpage - read an entire page in from 9P
   *
   * @filp: file being read
   * @page: structure to page
   *
   */
  
  static int v9fs_vfs_readpage(struct file *filp, struct page *page)
  {
  	return v9fs_fid_readpage(filp->private_data, page);
  }
  
  /**
   * v9fs_vfs_readpages - read a set of pages from 9P
   *
   * @filp: file being read
   * @mapping: the address space
   * @pages: list of pages to read
   * @nr_pages: count of pages to read
   *
   */
  
  static int v9fs_vfs_readpages(struct file *filp, struct address_space *mapping,
  			     struct list_head *pages, unsigned nr_pages)
  {
  	int ret = 0;
  	struct inode *inode;
  
  	inode = mapping->host;
  	p9_debug(P9_DEBUG_VFS, "inode: %p file: %p
  ", inode, filp);
  
  	ret = v9fs_readpages_from_fscache(inode, mapping, pages, &nr_pages);
  	if (ret == 0)
  		return ret;
  
  	ret = read_cache_pages(mapping, pages, (void *)v9fs_vfs_readpage, filp);
  	p9_debug(P9_DEBUG_VFS, "  = %d
  ", ret);
  	return ret;
  }
  
  /**
   * v9fs_release_page - release the private state associated with a page
   *
   * Returns 1 if the page can be released, false otherwise.
   */
  
  static int v9fs_release_page(struct page *page, gfp_t gfp)
  {
  	if (PagePrivate(page))
  		return 0;
  	return v9fs_fscache_release_page(page, gfp);
  }
  
  /**
   * v9fs_invalidate_page - Invalidate a page completely or partially
   *
   * @page: structure to page
   * @offset: offset in the page
   */
  
  static void v9fs_invalidate_page(struct page *page, unsigned int offset,
  				 unsigned int length)
  {
  	/*
  	 * If called with zero offset, we should release
  	 * the private state assocated with the page
  	 */
  	if (offset == 0 && length == PAGE_CACHE_SIZE)
  		v9fs_fscache_invalidate_page(page);
  }
  
  static int v9fs_vfs_writepage_locked(struct page *page)
  {
  	char *buffer;
  	int retval, len;
  	loff_t offset, size;
  	mm_segment_t old_fs;
  	struct v9fs_inode *v9inode;
  	struct inode *inode = page->mapping->host;
  
  	v9inode = V9FS_I(inode);
  	size = i_size_read(inode);
  	if (page->index == size >> PAGE_CACHE_SHIFT)
  		len = size & ~PAGE_CACHE_MASK;
  	else
  		len = PAGE_CACHE_SIZE;
  
  	set_page_writeback(page);
  
  	buffer = kmap(page);
  	offset = page_offset(page);
  
  	old_fs = get_fs();
  	set_fs(get_ds());
  	/* We should have writeback_fid always set */
  	BUG_ON(!v9inode->writeback_fid);
  
  	retval = v9fs_file_write_internal(inode,
  					  v9inode->writeback_fid,
  					  (__force const char __user *)buffer,
  					  len, &offset, 0);
  	if (retval > 0)
  		retval = 0;
  
  	set_fs(old_fs);
  	kunmap(page);
  	end_page_writeback(page);
  	return retval;
  }
  
  static int v9fs_vfs_writepage(struct page *page, struct writeback_control *wbc)
  {
  	int retval;
  
  	p9_debug(P9_DEBUG_VFS, "page %p
  ", page);
  
  	retval = v9fs_vfs_writepage_locked(page);
  	if (retval < 0) {
  		if (retval == -EAGAIN) {
  			redirty_page_for_writepage(wbc, page);
  			retval = 0;
  		} else {
  			SetPageError(page);
  			mapping_set_error(page->mapping, retval);
  		}
  	} else
  		retval = 0;
  
  	unlock_page(page);
  	return retval;
  }
  
  /**
   * v9fs_launder_page - Writeback a dirty page
   * Returns 0 on success.
   */
  
  static int v9fs_launder_page(struct page *page)
  {
  	int retval;
  	struct inode *inode = page->mapping->host;
  
  	v9fs_fscache_wait_on_page_write(inode, page);
  	if (clear_page_dirty_for_io(page)) {
  		retval = v9fs_vfs_writepage_locked(page);
  		if (retval)
  			return retval;
  	}
  	return 0;
  }
  
  /**
   * v9fs_direct_IO - 9P address space operation for direct I/O
   * @rw: direction (read or write)
   * @iocb: target I/O control block
   * @iov: array of vectors that define I/O buffer
   * @pos: offset in file to begin the operation
   * @nr_segs: size of iovec array
   *
   * The presence of v9fs_direct_IO() in the address space ops vector
   * allowes open() O_DIRECT flags which would have failed otherwise.
   *
   * In the non-cached mode, we shunt off direct read and write requests before
   * the VFS gets them, so this method should never be called.
   *
   * Direct IO is not 'yet' supported in the cached mode. Hence when
   * this routine is called through generic_file_aio_read(), the read/write fails
   * with an error.
   *
   */
  static ssize_t
  v9fs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
  	       loff_t pos, unsigned long nr_segs)
  {
  	/*
  	 * FIXME
  	 * Now that we do caching with cache mode enabled, We need
  	 * to support direct IO
  	 */
  	p9_debug(P9_DEBUG_VFS, "v9fs_direct_IO: v9fs_direct_IO (%s) off/no(%lld/%lu) EINVAL
  ",
  		 iocb->ki_filp->f_path.dentry->d_name.name,
  		 (long long)pos, nr_segs);
  
  	return -EINVAL;
  }
  
  static int v9fs_write_begin(struct file *filp, struct address_space *mapping,
  			    loff_t pos, unsigned len, unsigned flags,
  			    struct page **pagep, void **fsdata)
  {
  	int retval = 0;
  	struct page *page;
  	struct v9fs_inode *v9inode;
  	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
  	struct inode *inode = mapping->host;
  
  
  	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p
  ", filp, mapping);
  
  	v9inode = V9FS_I(inode);
  start:
  	page = grab_cache_page_write_begin(mapping, index, flags);
  	if (!page) {
  		retval = -ENOMEM;
  		goto out;
  	}
  	BUG_ON(!v9inode->writeback_fid);
  	if (PageUptodate(page))
  		goto out;
  
  	if (len == PAGE_CACHE_SIZE)
  		goto out;
  
  	retval = v9fs_fid_readpage(v9inode->writeback_fid, page);
  	page_cache_release(page);
  	if (!retval)
  		goto start;
  out:
  	*pagep = page;
  	return retval;
  }
  
  static int v9fs_write_end(struct file *filp, struct address_space *mapping,
  			  loff_t pos, unsigned len, unsigned copied,
  			  struct page *page, void *fsdata)
  {
  	loff_t last_pos = pos + copied;
  	struct inode *inode = page->mapping->host;
  
  	p9_debug(P9_DEBUG_VFS, "filp %p, mapping %p
  ", filp, mapping);
  
  	if (unlikely(copied < len)) {
  		/*
  		 * zero out the rest of the area
  		 */
  		unsigned from = pos & (PAGE_CACHE_SIZE - 1);
  
  		zero_user(page, from + copied, len - copied);
  		flush_dcache_page(page);
  	}
  
  	if (!PageUptodate(page))
  		SetPageUptodate(page);
  	/*
  	 * No need to use i_size_read() here, the i_size
  	 * cannot change under us because we hold the i_mutex.
  	 */
  	if (last_pos > inode->i_size) {
  		inode_add_bytes(inode, last_pos - inode->i_size);
  		i_size_write(inode, last_pos);
  	}
  	set_page_dirty(page);
  	unlock_page(page);
  	page_cache_release(page);
  
  	return copied;
  }
  
  
  const struct address_space_operations v9fs_addr_operations = {
  	.readpage = v9fs_vfs_readpage,
  	.readpages = v9fs_vfs_readpages,
  	.set_page_dirty = __set_page_dirty_nobuffers,
  	.writepage = v9fs_vfs_writepage,
  	.write_begin = v9fs_write_begin,
  	.write_end = v9fs_write_end,
  	.releasepage = v9fs_release_page,
  	.invalidatepage = v9fs_invalidate_page,
  	.launder_page = v9fs_launder_page,
  	.direct_IO = v9fs_direct_IO,
  };