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

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Date:	Mon, 28 Jan 2008 12:33:42 -0600
From:	"Steve French" <smfrench@...il.com>
To:	"Andi Kleen" <ak@...e.de>
Cc:	"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 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.


-- 
Thanks,

Steve
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