Future: Filesystem ACL and SCM
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.
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.
- 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.
Warren Togami
wtogami(a)redhat.com