linux-kernel - Re: [PATCH] d_ino considered harmful

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Date:	Wed, 16 Jun 2010 15:15:56 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	Valerie Aurora <vaurora@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Jan Blunck <jblunck@...e.de>,
	Jamie Lokier <jamie@...reable.org>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] d_ino considered harmful

On Wed, 16 Jun 2010 14:59:13 -0400
Valerie Aurora <vaurora@...hat.com> wrote:

> Who needs d_ino anyway?  I am running a kernel with this patch -
> Gnome, a browser, IRC, kernel compile, etc. and everything works.
> 
> -VAL
> 
> commit 184f3919d0071f3bfa40010aa6919ea89999d79b
> Author: Valerie Aurora <vaurora@...hat.com>
> Date:   Wed Jun 16 11:05:06 2010 -0700
> 
>     VFS: Always return 0 for d_ino
>     
>     Use of d_ino without the corresponding st_dev is always buggy in the
>     presence of submounts, bind mounts, and union mounts.  E.g., the d_ino
>     of a mountpoint will be the inode number of the directory under the
>     mountpoint, not the mounted directory.  Correct code must call stat(),
>     which returns the correct device ID and inode in st_dev and st_ino.
>     Since no one should be using d_ino anyway, always return 0 to detect
>     bugs.
> 
> diff --git a/fs/readdir.c b/fs/readdir.c
> index dd3eae1..38ea772 100644
> --- a/fs/readdir.c
> +++ b/fs/readdir.c
> @@ -91,7 +91,9 @@ static int fillonedir(void * __buf, const char * name, int namlen, loff_t offset
>  
>  	if (buf->result)
>  		return -EINVAL;
> -	d_ino = ino;
> +	/* Use of d_ino without st_dev is always buggy. */
> +	d_ino = 0;
> +
>  	if (sizeof(d_ino) < sizeof(ino) && d_ino != ino) {
>  		buf->result = -EOVERFLOW;
>  		return -EOVERFLOW;
> --
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> 

That may run afoul of the following check (where d_ino is compared to
ino). You can probably just remove that check though since you can be
reasonably sure that 0 will never overflow the field.

-- 
Jeff Layton <jlayton@...hat.com>
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