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Message-ID: <alpine.LFD.2.01.0906231019250.3240@localhost.localdomain>
Date: Tue, 23 Jun 2009 10:34:49 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Howells <dhowells@...hat.com>
cc: Miklos Szeredi <miklos@...redi.hu>, alan@...rguk.ukuu.org.uk,
hch@...radead.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk,
adilger@....com, akpm@...ux-foundation.org
Subject: Re: [RFC] O_NOACC: open without any access
On Tue, 23 Jun 2009, David Howells wrote:
> Miklos Szeredi <miklos@...redi.hu> wrote:
>
> > Define O_NOACC as 3. On open(..., O_FILESYSTEM | O_NOACC) require no
> > privileges on the file.
>
> It must also work with O_NOFOLLOW, which I think your suggestion will.
This does sound like a fairly natural extension of what we already do.
We essentially already have O_NOACCESS (3), and use it exactly because we
need to do operations on a file descriptor without "real" accesses
(notably things like accessing /dev/cdrom without waiting/checking for the
disk being present etc).
O_FILESYSTEM I don't like as a name (to me, it doesn't say _what_ it is
doing - of course an open works on a filesystem!), but the concept of
saying "don't follow device nodes - just open the node itself" makes
perfect sense. Together with O_NOFOLLOW it also fairly naturally means
"give me the actual symlink _node_, don't return error or follow it".
And we can trivially test at a higher level that O_FILESYSTEM (with a
better name, please), is always paired with O_NOACCESS (not O_NOACC: we do
not try to save three letters, there is no shortage). Because the raw node
obviously must never really be "accessed" (ie you can't do read/write etc
on it).
That said, I do _not_ like the notion of
> Add a new inode->i_filesystem_fop pointer
regardless of whether it's in inode->i_op or wherever. I think we should
just handle this in the regular "inode->f_op->open" routine, the same way
we handle FMODE_EXCLUSIVE (O_EXCL), FMODE_NDELAY (O_NONBLOCK) and lack of
access rights (O_NOACCESS) in the driver open routines that currently
handle those specially (O_NDELAY is spe
Al?
Linus
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