Re: [reiserfs-list] Re: [REISERFS TESTING] new patches on ftp.namesys.com: 2.4.15-pre7

Jeff Mahoney
2001-11-21T16:53:20Z

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On Wed, Nov 21, 2001 at 03:18:21PM +0300, Nikita Danilov wrote:
> Dieter Nützel writes:
> > PS Have you read about the latest ACL discussion on LKML?
>
> Yes, but Hans thinks we shouldn't do ACL reiserfs 3.x and concentrate on
> v4 in stead. You can try to persuade him though. Same for extended
> attributes.

I started to write ACL support based on Andreas Grünbacher's patches at
http://acl.bestbits.at a few months ago. Since there was no decided upon
format, I stopped development so that I wouldn't leave non-standard
filesystems in my wake. Once the ACL/EA format/API is finalized, I'll
probably continue development on it.

On a more technical note, adding a new item type, such as an
extended attribute item will cause problems for implementations that
don't know about them. An idea kicked around a few months ago was to
simply change the version string so that implementations that don't
know about ACL support can't mount the new version. "can't mount"
could conceivably be changed to "can only mount read-only", but certainly
not read-write, since non-solid items need special handling (every item
but stat data is non-solid).

This creates the following scenario:
* Versions that don't know about the new version string will
refuse to mount the fs.
* Versions that know about the new version, but don't implement support
will be read-only. This is because items get moved during balancing, even
to un-related items. Knowledge of the inside non-solid items is required
to move them around. So, even if there is a single ACL on the system, in
some deep directory, it could affect balancing (cause a panic).
* Versions that know about the new version, and implement support will
be read-write.

I see something along the lines of EXT2's compatibility matrix happening
here, but due to the inherent incompatibilities, this may not be a prime
candidate for 2.4 inclusion.

-Jeff

--
Jeff Mahoney | "Bill Gates is a monocle and a Persian cat away
jeffm@suse.com | from being the villain in a James Bond movie."
jeffm@csh.rit.edu | -- Dennis Miller

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