/*
 * Copyright (c) 2015, The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only 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.
 *
 */

#include "fuse_shortcircuit.h"

#include <linux/aio.h>
#include <linux/fs_stack.h>

void fuse_setup_shortcircuit(struct fuse_conn *fc, struct fuse_req *req)
{
	int daemon_fd;
	struct file *rw_lower_file = NULL;
	struct fuse_open_out *open_out;
	int open_out_index;

	req->private_lower_rw_file = NULL;

	if (!(fc->shortcircuit_io))
		return;

	if ((req->in.h.opcode != FUSE_OPEN) &&
	    (req->in.h.opcode != FUSE_CREATE))
		return;

	open_out_index = req->in.numargs - 1;

	BUG_ON(open_out_index != 0 && open_out_index != 1);
	BUG_ON(req->out.args[open_out_index].size != sizeof(*open_out));

	open_out = req->out.args[open_out_index].value;

	daemon_fd = (int)open_out->lower_fd;
	if (daemon_fd < 0)
		return;

	rw_lower_file = fget_raw(daemon_fd);
	if (!rw_lower_file)
		return;
	req->private_lower_rw_file = rw_lower_file;
}

static ssize_t fuse_shortcircuit_aio_read_write(struct kiocb *iocb,
						const struct iovec *iov,
						unsigned long nr_segs,
						loff_t pos, int do_write)
{
	ssize_t ret_val;
	struct fuse_file *ff;
	struct file *fuse_file, *lower_file;
	struct inode *fuse_inode, *lower_inode;

	ff = iocb->ki_filp->private_data;
	fuse_file = iocb->ki_filp;
	lower_file = ff->rw_lower_file;

	/* lock lower file to prevent it from being released */
	get_file(lower_file);
	iocb->ki_filp = lower_file;
	fuse_inode = fuse_file->f_path.dentry->d_inode;
	lower_inode = lower_file->f_path.dentry->d_inode;

	if (do_write) {
		if (!lower_file->f_op->aio_write)
			return -EIO;

		ret_val = lower_file->f_op->aio_write(iocb, iov, nr_segs, pos);

		if (ret_val >= 0 || ret_val == -EIOCBQUEUED) {
			fsstack_copy_inode_size(fuse_inode, lower_inode);
			fsstack_copy_attr_times(fuse_inode, lower_inode);
		}
	} else {
		if (!lower_file->f_op->aio_read)
			return -EIO;

		ret_val = lower_file->f_op->aio_read(iocb, iov, nr_segs, pos);
		if (ret_val >= 0 || ret_val == -EIOCBQUEUED)
			fsstack_copy_attr_atime(fuse_inode, lower_inode);
	}

	iocb->ki_filp = fuse_file;
	fput(lower_file);
	/* unlock lower file */

	return ret_val;
}

ssize_t fuse_shortcircuit_aio_read(struct kiocb *iocb, const struct iovec *iov,
				   unsigned long nr_segs, loff_t pos)
{
	return fuse_shortcircuit_aio_read_write(iocb, iov, nr_segs, pos, 0);
}

ssize_t fuse_shortcircuit_aio_write(struct kiocb *iocb, const struct iovec *iov,
				    unsigned long nr_segs, loff_t pos)
{
	return fuse_shortcircuit_aio_read_write(iocb, iov, nr_segs, pos, 1);
}

void fuse_shortcircuit_release(struct fuse_file *ff)
{
	if (!(ff->rw_lower_file))
		return;

	/* Release the lower file. */
	fput(ff->rw_lower_file);
	ff->rw_lower_file = NULL;
}