inotify on Samba4 and clustering

[Andrew Bartlett]

On Tue, 2006-05-30 at 16:38 -0500, Abhijith Das wrote:
> Hi list,
> I was looking at the latest Samba4 code and found some use of the 
> inotify interface. I was told before that dnotify was being replaced by 
> inotify, so this is not a surprise.
> However, when I think of a clusterized implementation of inotify for 
> GFS, I see complications.
>  - An event-watch on one cluster node should be propagated to all nodes.
>  - When an event occurs on a different node, we need to somehow write to 
> the event-queue of the first node. This could mean some serious hacking.
>  - There are way too many events to use a distributed-lock-manager's 
> locking for internode communication. A separate userland event/messaging 
> framework would have to deal with these event notifications and pass 
> them around as necessary.
> 
> Is the effort worth the reward? In what situations does samba use 
> inotify and what could be the performance impact without inotify support?

It is not a performance, but a correctness impact.  Windows clients use
change notify, (which we back onto inotify) frequently, and expect it to
work.  The simple case is that explorer won't update the display when a
remote user deletes a file, but it goes far beyond that.

> An alternate solution could be a local-inotify implementation. We could 
> add support in clustered-samba to pass these inotify messages to various 
> cluster nodes as appropriate?

I think this belongs in the filesystem, but somehow, every node that
might change these files must watch for them. 

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org
Student Network Administrator, Hawker College  http://hawkerc.net
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