[ENBD] proxing ioctl's

[Daniel Shane]

> What was the file? I had a look at the ramfs driver, but they use
> pages.

Its rd.c in drivers/block, in the do_rd_request() function. 

> > ever freeing the pages that we write to. Therefore, we dont need
> > to handle writes at all, the buffer cache manages it for us. What
> > do you think about integrating this approach in nbd?
> 
> As far as I could see from the ramfs stuff, they take care to mark
> their page dirty just after releasing it. One can do something similar
> by modifying the endio call on blocks. Just leave them marked dirty.

All we need to do is mark the page undeletable, and when we close
the connection to a server, just destroy the reserved buffers.

It looks like a 4 or 5 lines of code max to implement client 
side journaling. I even think it would be more efficient that
the current solution. 
 
Daniel.