Re: [RFC][PATCH 5/5] make open_namei() return a filp

[Christoph Hellwig <hch@infradead.org>]

On Thu, Sep 27, 2007 at 11:52:15AM -0700, Dave Hansen wrote:
> If open_namei() succeeds, there is potentially a mnt_want_write()
> that needs to get balanced.  If the caller doesn't create a
> 'struct file' and eventually __fput() it, or manually drop the
> write count on an error, we have a bug.
> 
> Forcing open_namei() to return a filp fixes this.  Any caller
> getting a 'struct file' back must consider that filp instantiated
> and fput() it normally.  The callers no longer have to worry about
> ever manually releasing a mnt write count.

> diff -puN fs/open.c~make-open_namei-return-a-filp fs/open.c
> --- lxc/fs/open.c~make-open_namei-return-a-filp	2007-09-27 11:51:34.000000000 -0700
> +++ lxc-dave/fs/open.c	2007-09-27 11:51:34.000000000 -0700
> @@ -846,11 +846,7 @@ static struct file *do_filp_open(int dfd
>  	int error;
>  	struct nameidata nd;
>  
> -	error = open_namei(dfd, filename, flags, mode, &nd);
> -	if (!error)
> -		return nameidata_to_filp(&nd, flags);
> -
> -	return ERR_PTR(error);
> +	return open_namei(dfd, filename, flags, mode, &nd);

Error is unused now, and it's also rather silly to allocate the
nd here when it's only used inside open_namei.  So I'd suggest
killing do_filp_open, and maybe filp_open aswell while you're at
it.