linux-kernel - Re: [PATCH 2/2] vfs: fix d_path() for unreachable paths

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Message-ID: <20090921144336.GF14381@ZenIV.linux.org.uk>
Date:	Mon, 21 Sep 2009 15:43:36 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Valdis.Kletnieks@...edu, agruen@...e.de, hch@....de,
	hugh.dickins@...cali.co.uk, matthew@....cx
Subject: Re: [PATCH 2/2] vfs: fix d_path() for unreachable paths

On Mon, Sep 21, 2009 at 03:38:57PM +0100, Al Viro wrote:
> On Mon, Sep 21, 2009 at 10:10:17AM -0400, Mike Frysinger wrote:
> 
> > it works without having to copy & paste the same exact structures over
> > and over.  a suggestion as how to do it cleanly without bloating the
> > code is certainly welcome.  it doesnt really matter that it's on the
> > stack as the usage is small and d_path() is given the size of the
> > buffer, so it isnt going to overflow.
> 
> Umm...  Surely, you can put a CPU number + one bit into PDE->data?  As in
> 	proc_create_data("icplb", ....., (void *)(cpu * 2))
> 	proc_create_data("dcplb", ....., (void *)(cpu * 2 + 1))
> and
> 	struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
> 	unsigned long n = (unsigned long) pde->data;
> 	...
> 	cpu = n / 2;
> 	is_D = n & 1;

PS: as to why it is broken...  Consider e.g.
	mount --bind /proc/cplbinfo/cpu0 /mnt
	cat /mnt/icplb
Or, better yet,
	mount -t proc none /mnt/cpu
	cat /mnt/cpu/cplbinfo/cpu0/icplb
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