linux-kernel - Re: [PATCH v5] fuse: Add support for passthrough read/write

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Message-ID: <20160201191555.GA3524@pc.thejh.net>
Date:	Mon, 1 Feb 2016 20:15:56 +0100
From:	Jann Horn <jann@...jh.net>
To:	Nikhilesh Reddy <reddyn@...eaurora.org>
Cc:	torvalds@...ux-foundation.org, Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	gregkh@...uxfoundation.org, linux-fsdevel@...r.kernel.org,
	viro@...iv.linux.org.uk, Richard Weinberger <richard@....at>,
	Theodore Ts'o <tytso@....edu>, jack@...e.cz,
	Antonio SJ Musumeci <trapexit@...wn.link>, sven.utcke@....de,
	Nikolaus Rath <nikolaus@...h.org>,
	Jann Horn <jannhorn@...glemail.com>,
	Mike Shal <marfey@...il.com>
Subject: Re: [PATCH v5] fuse: Add support for passthrough read/write

On Mon, Feb 01, 2016 at 10:56:27AM -0800, Nikhilesh Reddy wrote:
> diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
[...]
> +static ssize_t fuse_passthrough_read_write_iter(struct kiocb *iocb,
> +					    struct iov_iter *iter, int do_write)
> +{
> +	ssize_t ret_val;
> +	struct fuse_file *ff;
> +	struct file *fuse_file, *passthrough_filp;
> +	struct inode *fuse_inode, *passthrough_inode;
> +
> +	ff = iocb->ki_filp->private_data;
> +	fuse_file = iocb->ki_filp;
> +	passthrough_filp = ff->passthrough_filp;
> +
> +	/* lock passthrough file to prevent it from being released */
> +	get_file(passthrough_filp);
> +	iocb->ki_filp = passthrough_filp;
> +	fuse_inode = fuse_file->f_path.dentry->d_inode;
> +	passthrough_inode = file_inode(passthrough_filp);
> +
> +	if (do_write) {
> +		if (!passthrough_filp->f_op->write_iter)
> +			return -EIO;
> +		ret_val = passthrough_filp->f_op->write_iter(iocb, iter);
> +
> +		if (ret_val >= 0 || ret_val == -EIOCBQUEUED) {
> +			fsstack_copy_inode_size(fuse_inode, passthrough_inode);
> +			fsstack_copy_attr_times(fuse_inode, passthrough_inode);
> +		}
> +	} else {
> +		if (!passthrough_filp->f_op->read_iter)
> +			return -EIO;
> +		ret_val = passthrough_filp->f_op->read_iter(iocb, iter);
> +		if (ret_val >= 0 || ret_val == -EIOCBQUEUED)
> +			fsstack_copy_attr_atime(fuse_inode, passthrough_inode);
> +	}
> +
> +	iocb->ki_filp = fuse_file;
> +
> +	/* unlock passthrough file */
> +	fput(passthrough_filp);

Why the get_file() and fput() in this method? This doesn't look right. There
is no lock you're releasing between get_file() and fput(). What are they
intended for?

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