Messages in this thread | | | From | Bear Giles <> | Subject | Re: Ext3 filesystem info? | Date | Sat, 25 Sep 1999 20:39:07 -0600 (MDT) |
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> The problem is that different, already established filesystems: AFS, > Coda, NTFS, etc., all have different ACL semantics. For example, AFS > only has an ACL on a per-directory basis. I'm not sure about Coda, but > it may be the same as AFS. NTFS uses 128 bit UUID's in its ACL's to > name users and groups. The POSIX acl interface uses uid_t and gid_t for > user and group id's.
Since I haven't seen anyone else ask this...
... why are we worried about compatibility with NTFS? Or with distributed file systems?
I'm not arguing that such support isn't a good idea, only that we seem to be putting the cart before the horse here. Let's get *native* ACL support into our filesystems. By "native" I mean that it uses the same information we already require filesystems to understand (uid_t, gid_t).
N.B., as I understand ACLs they will be enforced by the file system module, not the general kernel VFS level or user libraries. Unless I'm mistaken the only extensions required to the VFS level are:
struct acl { uid_t uid; /* uid or UID_ANY */ gid_t gid; /* gid or GID_ANY */ int permissions; /* R_OK, W_OK, X_OK, etc. */ };
ssize_t write_acls (int mode, const struct acl *acls, size_t size); ssize_t read_acls (int mode, struct acl *acls, size_t size);
where mode = 0 for discretionary access control (user can modify) and mode = 1 for non-discretionary access control (user can't modify, but root or CAPACITY_NDAC(?) can.)
You don't need to have "positive" and "negative" flags if you follow the policy that the best match dominates. You could remove 'bob' from your group's permissions by:
(bob,group: ---) (%,group: rw-)
Finally, once that's stable we can decide how to handle non-native ACLs (e.g., those that require 128-bit UUIDs). We might lose some of the transparency that VFS is intended to provide, but that's an unfortunate reflection of the tremendous variety in how different groups handle ACLs. I would hate to see us delay ACLs for months so we can handle NTFS, only to have that filesystem be changed in a way that invalidates the work.
Bear Giles bgiles@coyotesong.com
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