linux-kernel - Re: [RFC] O_NOACC: open without any access

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Message-Id: <E1MJ8u3-00083c-TD@pomaz-ex.szeredi.hu>
Date:	Tue, 23 Jun 2009 18:31:23 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	dhowells@...hat.com
CC:	alan@...rguk.ukuu.org.uk, dhowells@...hat.com, miklos@...redi.hu,
	hch@...radead.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.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:
> Reference count on which module?  This would not take a reference on
> the device driver as it would not refer to it, but would still have
> a file struct, an inode struct and a dentry struct on the underlying
> fs.

So how about the following: provide a new open flag O_FILESYSTEM,
meaning it opens the file on the underlying filesystem instead of the
device/socket/symlink/etc...

Add a new inode->i_filesystem_fop pointer which is used instead of
inode->i_fop in case if O_FILESYSTEM.  If ->i_filesystem_fop isn't set
by the filesystem, fall back to a default which returns -EBADF for all
operations (except open).

Define O_NOACC as 3.  On open(..., O_FILESYSTEM | O_NOACC) require no
privileges on the file.

AFS would set up i_filesystem_fop with its ->ioctl() function. No
special handling needed for revoke()...

That would work, no?

Thanks,
Miklos

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