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

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Date:	Thu, 22 Apr 2010 17:20:23 +0200
From:	Jan Kara <jack@...e.cz>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	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 Thu 22-04-10 12:08:55, David Woodhouse wrote:
> 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.
  Yes, that's what I meant by my suggestion... Sorry if I wasn't clear
enough.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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