linux-kernel - Re: [PATCH, RFC] tty: stop abusing file->f_u.fu

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Date:	Tue, 8 Jun 2010 15:22:52 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH, RFC] tty: stop abusing file->f_u.fu_list

On Fri, Jun 04, 2010 at 02:39:34PM -0400, Christoph Hellwig wrote:
> The ttry code currently abuses the file anchor for the per-sb file list
> to track instances of a given tty.  But there's no good reason for
> that, we can just install a proxy object in file->private that gets
> added to the list and points to the tty and keep the list away from
> VFS internals.

Well this code looks like the error handling is broken and it's pretty
convoluted to fix (eg. tty_release requires tty from filp but is called
to clean up code from before tty file private structure is allocated).

So I really prefer to put my original patch first. I really don't see
how it makes the tty code more of a special case. In both cases, it
must know that the vfs does not require the file's presence on the
s_files list so it can be reused for tty code. After my patch, it no
longer knows any details about how the vfs does locking for the list.

Possibly a lighter way to do what you want is to have the vfs not use
fu_list for device inodes and define drivers to be allowed to use it for
their own purpose. But that is easily possible after my patch.

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