Re: Unionmount. Basic details

[Da Zheng]

Hi,

Carl Fredrik Hammar wrote:
> > It is not fully clear right now -- I realized that there is another
> > decision to make: should the unionmount translator be directly visible
> > as the translator attached to the mount node; or should it serve as a
> > proxy, forwarding all requests on the filesystem port to the target
> > translator -- thus making itself more or less transparent, so it appears
> > as if the target was attached to the mount node directly?
> >
> > I tend towards the latter.
> >     
>
> I think the latter makes a lot more sense.  I can't think of any reason
> to let the mountee be aware that it's detached from the underlying
> file system.  If anything it would just confuse it.
>   
I think the first approach has its advantage. One very important reason 
is the performance. We are writing OS, after all.
With the second approach, all requests from the application to the file 
system are twice expensive as before.
But with the first approach it is possible that unionmount translator 
can expose the port to the node in the underlying file system to the 
outside world and later the application can access the underlying node 
with that port directly (unionmount isn't involved in the following 
operations such as reading and writing).
I might be mistaken. I don't know much how unionfs works and whether 
unionmount can work in this way.

Zheng Da