linux-kernel - Re: How to locate struct file * from a bio?

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Message-ID: <20070131145154.GA19815@ftp.linux.org.uk>
Date:	Wed, 31 Jan 2007 14:51:54 +0000
From:	Al Viro <viro@....linux.org.uk>
To:	Eddie Pettis <pettis.eddie@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: How to locate struct file * from a bio?

On Wed, Jan 31, 2007 at 02:44:23PM +0000, Al Viro wrote:
> On Wed, Jan 31, 2007 at 09:34:54AM -0500, Eddie Pettis wrote:
> > Short question:  Is it possible to locate the struct file * associated
> > with a bio?  If so, how?
>  
> Obviously impossible.  For one thing, there might very well be no inode,
> let alone struct file, associated with bio in question (e.g. for any
> filesystem metadata).  Moreover, the same on-disk object may get IO
> without any stuct file at all (e.g. a directory) or with many struct
> file (e.g. any file independently opened by several processes; no matter
> how many of them do reads, we'll get stuff pulled into page cache the
> same way (and once, not once per struct file).

BTW, here's a good testcase for you: /etc/ld.so.cache; it's accessed at
practically any execve(), so it should be very close to top of the
popularity list (right there with /lib/libc.so.6)...
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