linux-kernel - Re: [PATCH -V7 21/26] richacl: xattr mapping functions

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Date:	Thu, 20 Oct 2011 16:32:04 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>,
	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	agruen@...nel.org, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, dhowells@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V7 21/26] richacl: xattr mapping functions

On Thu, 20 Oct 2011 05:19:46 -0400, Christoph Hellwig <hch@...radead.org> wrote:
> On Thu, Oct 20, 2011 at 05:14:34AM -0400, J. Bruce Fields wrote:
> > > > Does it really make sense to use a string here just to pick between the
> > > > three choices OWNER@, GROUP@, and EVERYONE@?  Why not just another small
> > > > integer?  Is the goal to expand this somehow eventually?
> > > 
> 
> > > I guess Andreas wanted the disk layout to be able to store user@...ain
> > > format if needed.
> > 
> > Is that likely?  For that to be useful, tasks would need to be able to
> > run as user@...ain strings.  And we'd probably want owners and groups to
> > also be user@...ain strings.
> > 
> > The container people seem to eventually want to add some kind of
> > namespace identifier everywhere:
> > 
> > 	http://marc.info/?l=linux-kernel&m=131836778427871&w=2
> > 
> > in which case I guess we'd likely end up with (uid, user namespace id)
> > instead of user@...ain?
> 
> 
> Storing strings is an extremly stupid idea.  The only thing that would
> make sense would be storing a windows-style 128-bit GUID.
> 

How about updating the richacl_xattr as below 

struct richace_xattr {
	__le16		e_type;
	__le16		e_flags;
	__le32		e_mask;
	__le32		e_size;
	u8		e_id[0];
};

now e_flags can contain ACE4_SPECIAL_WHO to indicate value in e_id
indicate special who values (which could be 1 byte value indicating
OWNER@, GROUP@ or EVERYONE@), ACE4_UNIXID_WHO, to indicate value
in e_id is the little endian value of unix id. ACE_WINSID_WHO to
indicate e_id is the 128 bit array containing SID value. ?

-aneesh

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