Re: Thinking outside the box on file systems

[Valdis.Kletnieks@vt.edu]

On Fri, 17 Aug 2007 11:19:21 EDT, Phillip Susi said:
> Kyle Moffett wrote:
>> Problem 1: "updating cached acls of descendent objects":  How do you 
>> find out what a 'descendent object' is?  Answer:  You can't without 
>> recursing through the entire in-memory dentry tree.

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.

(Does anybody know offhand what means 'chacl -r' uses to avoid race conditions
with directories being moved in/out from under it, or does it just say "we'll
make a best stab at it"?)

> Yes, it would take some cpu time, and yes, it would have to use a lock 
> to protect the acl which would also lock out moves.  Is that such a high 
> cost?  Changing acls and moving whole directory trees around is not THAT 
> common of an operation... if it takes a wee bit more cpu time, I doubt 
> anyone will complain.

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.

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