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From
SubjectRe: Implementing Meta File information in Linux
Date
In article <mng==199809131913.PAA25548@hilfy.ece.cmu.edu>, "Brandon S.
Allbery KF8NH" <allbery@kf8nh.apk.net> wrote:

> No, this won't help if the user isn't logged in when a deletion occurs that
> would affect their personal desktop database. Then again, OS/2 has similar
> issues (delete a file with WPS information when the WPS isn't running; not
> all WPS information is stored in extended attributes) and nevertheless
> survives --- in this case by not doing anything about it, hence the market
> for third-party products that clean up the desktop database. On Linux it
> would be better to have a low-priority process running alongside the desktop
> which cleans the database, or perhaps a cron job that runs weekly.

I promise to you that any such scheme will be a maintenance nightmare. One
of the really interesting calls is rename, this really makes any external
meta data storage concept problematic. In particular imagine a larger
departmental server hosting the files of a bunch of people. All these
people do work concurrently and add, delete and rename files. You can not
easily make that a cleanup task from cron, it has to happen in real time.
Users just expect to have changes pop up in their windows automatically.

Renames in particular have the nice semantic to be atomic, if you keep
meta data externally that breaks. Imagine one person saving a file, an app
renaming the old version and renaming the new version properly saved to
disk to the desired file name. Another user might at the same time move
the file to a different directory, which is a rename as well. There is a
hell of race conditions in that if meta data is not renamed transparently
with the main data.

The Mac file system handles this transparently for the users, one of the
strong points of this system.
--
Jens-Uwe Mager <pgp-mailto:62CFDB25>

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