[ENBD] proxing ioctl's

[Peter T. Breuer]

"A month of sundays ago Daniel Shane wrote:"
> Sure, I would like nbd to be able to emulate any block device.

You want to handle the ioctls as well as the read/write calls.

> Lets say, for example, that I would like to emulate the floppy
> driver. Well... the floppy driver uses special ioctls, and some
> of them might pass pointers to structures (not just an int or a char)
> as arguments to the ioctl call. 

maybe, maybe not. I don't know. The problem is that the context for
those is on the client, not on the server.

> The problem is, if its the client that is calling the ioctl and the 
> server that is executing it, we need to be able to transfer that 
> structure to the other end. Serializing the structure is impossible 
> since we need somekind of reflexion to parse it and I 
> dont know if we can do something on the server end to redirect the 
> memory access to the client in a general way... 
> 
> I was guessing that we could play with memory relocation. Not sure 
> though.
> 

OK. I'll reply later.

> BTW: About client journaling, I just took a look at the ram disk
> driver and they use a clever trick which I think we could use. They
> use the buffer cache as the ramdisk by preventing the kernel from 
> 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?

Could do. I'll look.

Peter