linux-kernel - Re: [PATCH] [8/18] BKL-removal: Remove BKL from remote

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Date:	Mon, 28 Jan 2008 19:34:39 +0000
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	Steve French <smfrench@...il.com>
Cc:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	swhiteho@...hat.com, sfrench@...ba.org, vandrove@...cvut.cz,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] [8/18] BKL-removal: Remove BKL from remote_llseek


On Mon, 2008-01-28 at 12:33 -0600, Steve French wrote:
> On Jan 28, 2008 2:17 AM, Andi Kleen <ak@...e.de> wrote:
> > > I completely agree.  If one thread writes A and another writes B then the
> > > kernel should record either A or B, not ((A & 0xffffffff00000000) | (B &
> > > 0xffffffff))
> >
> > The problem is pretty nasty unfortunately. To solve it properly I think
> > the file_operations->read/write prototypes would need to be changed
> > because otherwise it is not possible to do atomic relative updates
> > of f_pos. Right now the actual update is burrowed deeply in the low level
> > read/write implementation. But that would be a huge impact all over
> > the tree :/
> 
> If there were a wrapper around reads and writes of f_pos as there is
> for i_size e.g. it would hit a lot of code, but not as many as I had
> originally thought.  the most important ones are in the vfs itself, where
> there are only 59 uses of the field (not all need to be changed).   ext3
> has fewer (25), and cifs only 12 uses.

Most of the uses in ext3 and cifs deal with a directory's f_pos in
readdir, which is protected by i_mutex, so I don't think we need to
worry about them at all.
-- 
David Kleikamp
IBM Linux Technology Center

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