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choice of 'namespace' for ACL's

To: Linux-Xfs <linux-xfs@xxxxxxxxxxx>
Subject: choice of 'namespace' for ACL's
From: Linda Walsh <xfs@xxxxxxxxx>
Date: Fri, 19 Jul 2013 01:52:47 -0700
Delivered-to: linux-xfs@xxxxxxxxxxx
User-agent: Thunderbird


I was looking at the attr and it left me a bit puzzled.

(1) Of minor consideration, was the statement about 'values can be up
to 64KB'...  But there is no mention of how many names can be present
or if there is a cumulative maximum on the names or on the data.  I thought
I remembered there was, but all I found was limits on single datums.

(2) A more confusing issue was the bit describing XFS as having 2
disjoint attrib
namespaces, but later the selectors for the names spaces are given as
[none] = user, [R] = root, and [S] = Security -- making it sound like 3
disjoint
namespaces.  So, how many attrib namespaces are their, 2 or 3?

(3) Adding a bit more to pique my curiosity, I noticed that
file ACL's were in the root-namespace, not the security attribute namespace.
Wouldn't it make more sense if access control was considered a security
attrib?


Another point of confusion was on the attrib manpage where it says:
CAVEATS
       The list option present in the IRIX version of this command is
not supâ
       ported.  getfattr provides a mechanism to retrieve all of the
attribute
       names.

(4) What does that mean?  i.e.:

when I use attr -l:

> attr -l openssh-6.1p1-hpn13v14.diff.gz
Attribute "DOSATTRIB" has a 56 byte value for openssh-6.1p1-hpn13v14.diff.gz
Attribute "SAMBA_PAI" has a 25 byte value for openssh-6.1p1-hpn13v14.diff.gz

or addint the -q switch with -l:

> attr -ql openssh-6.1p1-hpn13v14.diff.gz
DOSATTRIB
SAMBA_PAI
---
Does "not supported" mean that it is working by accident and may be
removed   ... because....[_________???______]? 

getfattr is suggested as a replacement, but
(5) how can it be used to list the lengths?  and
(6) how can it be used to list the Security or Root namespaces?

Sorry for all the Q's, but it seemed like there were some missing pieces...



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