Extending text-format ACLs

[Tim Kientzle]

Implementing ACL support for tar is a tricky business.  In
particular, POSIX.1e draft 17 seems to overlook a critical
point:  archived ACL information *MUST* contain both
username/groupname and uid/gid.  That's the only way you can
correctly support situations where user information may
be unavailable[1] or have changed[2].

Joerg Schilling's solution with 'star' was
to add an ID field, e.g.,

    user:testuser:rw-:1798

Joerg claims this is compatible with POSIX.1e,
which seems reasonable to me, and I've implemented
this in my own libarchive.  However, I notice
that FreeBSD's acl_from_text, in particular,
chokes on this format.

Question:  Are there alternatives that have been
implemented elsewhere?  (At a minimum, I would
like libarchive to be able to read any common ACL
format.)

Question:  Should FreeBSD's implementation of
acl_from_text or text_from_acl support this?
(Possibly simply by ignoring the additional field?)

Tim Kientzle


[1] Consider the case where someone is trying
to clean up a trojaned system by restoring from
backups while disconnected from NIS.  In this case,
user/group names are not useful; numeric IDs are
essential.

[2] Consider a case where separately-maintained
systems are being brought under a common NIS
domain, requiring user/group IDs to change.
In this case, user/group names must be used on
restore.  In particular, a system that hopes to support
both of these examples must store both names and
numeric IDs.  POSIX.1e draft 17 does not provide
an explicit mechanism for doing so, hence the need
for an extension.


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