Re: Thinking outside the box on file systems

From: Phillip Susi
Date: Fri Aug 17 2007 - 15:01:47 EST


Valdis.Kletnieks@xxxxxx wrote:
I suspect Kyle is not quite correct - it's probably the case that you don't
have to consider just the in-memory dentries, but *all* the descendent objects
in the entire file system.

If you have a clever proof that on-disk can't *possibly* be affected, feel
free to present it.

Why would you have to consider the descendent entries on disk when you are only changing an entry in the parent? The effects of that change are only computed in memory when the dentry for a child is created, so you don't have to do a bunch of disk churning to change permissions on the whole tree. In fact, all of the children may very well have NO acl of their own stored on disk, which also saves space.

The whole idea here is that there is ONE acl that applies to the whole tree, rather than have every object in the tree have its own acl. That's why every object in the tree on the disk is not effected by a change.

It will become even *more* of a "not that common" if the lock will block moves
and ACL changes *across the filesystem* for potentially *minutes* at a time.

It will not take anywhere NEAR minutes at a time to update the in memory dentries, more like 50ms.




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