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Re: Future: Filesystem ACL and SCM



Dennis Gilmore wrote:
On Tuesday 20 March 2007 11:00:14 am Warren Togami wrote:
NOTE: This info is not relevant to the near-term Fedora merge or any
infrastructure supporting it.  We will continue to use the existing CVS
+ ACL system.

Toshio was wondering about the possibility of using filesystem ACL's as
part of a future ideal SCM's ACL enforcement.  It would work something
like this:
1) PackageDB knows about all packages, owners, granted permissions,
groups, etc.
2) PackageDB generates xattrs or FS ACL (themselves based on xattrs)
within the SCM files/directories.
3) SCM has a custom ACL enforcement script that reads those xattrs,
making it very fast and flexible.  ACL's could be enforced based on a
list of users, groups, or a combination of users and groups.
Sounds very sane to me
I talked with a few filesystem experts within Red Hat.  They said...
- ext3 has a limit of 4KB for xattr data.  If you use the standard
encoding of 8 bytes per uid, that has a limit of roughly 100 entities
that could be associated with a file.  Is this too limiting?  I dunno.
Perhaps it need not be too limiting if more extensive use of
group-based-ACL's are used.
I would like to encourage use of acls based on groups extensivly. i.e KDE SIG security etc. 8KB would probably be a little better but 4KB will be fine.

- XFS could possibly allow a maximum of 64KB xattr's per file, but that
is very inefficient in filesystem storage.
- xattr's are currently not supported by NFS.
i currently use linux ACL's over nfs very effectively
I forgot to mention this to the list but we are currently using ACL's effectively with the docs team. Basically all the translators have access to the doc's cvs /cvs/docs/*/po/ using the extended acls. I have a script that runs regularly that sets up these perms.

   -Mike


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