linux-kernel - Re: [PATCH] mtd: Do not corrupt backing device for inode

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Date:	Thu, 22 Apr 2010 12:08:55 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Jan Kara <jack@...e.cz>, Alexander Viro <viro@...iv.linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Alexander Shishkin <virtuoso@...nd.org>,
	linux-mtd@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: Do not corrupt backing device for inode

On Wed, 2010-04-21 at 18:21 +0300, Kirill A. Shutemov wrote:
> +		/*
> +		 * We cannot modify file->f_mapping->backing_dev_info directly,
> +		 * because it will corrupt backing device for inode, since
> +		 * inode->i_mapping is equal to file->f_mapping. So we have to
> +		 * copy f_mapping first.
> +		 */
> +		file->f_mapping = kmalloc(sizeof(*file->f_mapping), GFP_KERNEL);
> +		memcpy(file->f_mapping, inode->i_mapping,
> +				sizeof(*file->f_mapping));
>  		file->f_mapping->backing_dev_info = mtd->backing_dev_info;
> +	}

Ick. What about the rest of file->f_mapping? That'll still be inherited.

Jan pointed at drivers/char/raw.c as an example, but that doesn't do
anything as ugly as this -- that sets file->f_mapping to point at
bdev->bd_inode->i_mapping instead.

I suspect we should do something similar -- have an inode for the MTD
device, with a valid i_data of its own.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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