/*
 *  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/uio.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, "\n");

	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\n", 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\n", 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)
{
	struct inode *inode = page->mapping->host;
	struct v9fs_inode *v9inode = V9FS_I(inode);
	loff_t size = i_size_read(inode);
	struct iov_iter from;
	struct bio_vec bvec;
	int err, len;

	if (page->index == size >> PAGE_CACHE_SHIFT)
		len = size & ~PAGE_CACHE_MASK;
	else
		len = PAGE_CACHE_SIZE;

	bvec.bv_page = page;
	bvec.bv_offset = 0;
	bvec.bv_len = len;
	iov_iter_bvec(&from, ITER_BVEC | WRITE, &bvec, 1, len);

	/* We should have writeback_fid always set */
	BUG_ON(!v9inode->writeback_fid);

	set_page_writeback(page);

	p9_client_write(v9inode->writeback_fid, page_offset(page), &from, &err);

	end_page_writeback(page);
	return err;
}

static int v9fs_vfs_writepage(struct page *page, struct writeback_control *wbc)
{
	int retval;

	p9_debug(P9_DEBUG_VFS, "page %p\n", 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, struct iov_iter *iter, loff_t pos)
{
	struct file *file = iocb->ki_filp;
	if (rw == WRITE) {
		ssize_t written;
		int err = 0;

		written = p9_client_write(file->private_data, pos, iter, &err);
		if (written) {
			struct inode *inode = file_inode(file);
			loff_t i_size = i_size_read(inode);
			if (pos + written > i_size)
				inode_add_bytes(inode, pos + written - i_size);
			return written;
		}
		return err;
	}
	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\n", 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\n", 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,
};