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Re: [PATCH] Revised extended attributes interface

To: "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Subject: Re: [PATCH] Revised extended attributes interface
From: Hans Reiser <reiser@xxxxxxxxxxx>
Date: Tue, 11 Dec 2001 21:23:45 +0300
Cc: Nathan Scott <nathans@xxxxxxx>, Andreas Gruenbacher <ag@xxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-xfs@xxxxxxxxxxx, Nikita Danilov <god@xxxxxxxxxxx>
References: <20011205143209.C44610@wobbly.melbourne.sgi.com> <20011207202036.J2274@redhat.com> <20011208155841.A56289@wobbly.melbourne.sgi.com> <20011210115209.C1919@redhat.com> <20011211124115.E70201@wobbly.melbourne.sgi.com> <20011211134758.F2268@redhat.com>
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Stephen C. Tweedie wrote:



The proposal defines two "families" of attribute entities: attribute
families and name families.

An attribute family might be ATR_USER or ATR_SYSTEM to specify that we
are dealing with arbitrary user or system named extended attributes,
or ATR_POSIXACL to specify POSIX-semantics ACLs.  Obviously, this can
be extended to other ACL semantics without revving the API --- a new
attribute family would be all that is needed.

The "name family" is the other part of the equation.  Attributes in
the ATR_USER or ATR_SYSTEM families might be named with counted
strings, so they would have names in the ANAME_STRING name family.
POSIX ACLs, however, have a different namespace: ANAME_UID or
ANAME_GID.  The API cleanly deals with the difference between user and
group ACLs.  It also makes it easy to add support later on for more
complex operations: if we want to add NT SID support to ext2 ACLs so
that Samba and local accesses get the same access control, we can pass
ANAME_NTSID names to the ATR_POSIXACL attribute family without
changing the API.

If you have given it some thought, which your writing hints you may have, can you say a little about supporting NT SIDS and NT ACLs by Linux, and how that can be hard and easy?

One of my programmers is arguing that NT (as opposed to POSIX) ACL support is harder than I imagine due to SIDS, and.... your view would be interesting.

Hans


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