linux-kernel - Re: [PATCH v3] fuse: Add support for passthrough read/write

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Message-ID: <20160120233841.GA16235@pc.thejh.net>
Date:	Thu, 21 Jan 2016 00:38:41 +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.weinberger@...il.com>,
	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>
Subject: Re: [PATCH v3] fuse: Add support for passthrough read/write

On Wed, Jan 20, 2016 at 03:20:34PM -0800, Nikhilesh Reddy wrote:
> Add support for filesystem passthrough read/write of files
> when enabled in userspace through the option FUSE_PASSTHROUGH.
[...]
> +	daemon_fd = (int)open_out->passthrough_fd;
> +	if (daemon_fd < 0)
> +		return;
> +
> +	passthrough_filp = fget_raw(daemon_fd);
> +	if (!passthrough_filp)
> +		return;
> +
> +	passthrough_inode = file_inode(passthrough_filp);
> +	passthrough_sb = passthrough_inode->i_sb;
> +	fs_stack_depth = passthrough_sb->s_stack_depth + 1;
> +
> +	/* If we reached the stacking limit go through regular io */
> +	if (fs_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
> +		pr_err("FUSE: maximum fs stacking depth exceeded, cannot use passthrough for this file\n");
> +		return;
> +	}

I think this needs an fput() in the error case to prevent a refcount leak.

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