linux-kernel - Re: linux-next: Tree for Jun 26 [ vfs | block

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Message-ID: <20130626174656.6d9e2d2a@skate>
Date:	Wed, 26 Jun 2013 17:46:56 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	sedat.dilek@...il.com, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
	Jens Axboe <axboe@...nel.dk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel@...ts.sourceforge.net,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: linux-next: Tree for Jun 26 [ vfs | block | fuse (cpuidle)
 releated? ]

Dear Greg Kroah-Hartman,

On Wed, 26 Jun 2013 08:32:36 -0700, Greg Kroah-Hartman wrote:

> > Ok. My understanding is that the misc device registered by
> > fs/fuse/dev.c:fuse_dev_init() makes the assumption that
> > file->private_data == NULL when a misc device is opened. But I'm not
> > sure to fully understand the code flow of the FUSE filesystem.
> > 
> > And since it doesn't provide its own implementation of the ->open()
> > operation, the misc infrastructure was leaving the file->private_data
> > defined to NULL before my patch.
> > 
> > With my patch, the file->private_data gets assigned unconditionally
> > (regardless of whether the misc driver provides or does not provide a
> > ->open() operation) which modifies the unwritten assumption that fuse
> > was making about the initial value of file->private_data. I believe the
> > assumption made by fuse over the initial value of this variable is a
> > bit fragile.
> > 
> > Maybe the FUSE code needs to be slightly adjusted to not make this
> > assumption?
> 
> As the FUSE code was working properly before this change, I think this
> misc core change needs to be reverted, so I'll go do that in a bit.

Yes, sure, that's the right immediate action to take.

Long term, I believe the FUSE code seems to be making a fragile
assumption, and that might require some additional investigation.

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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