Re: [Nbd] [PATCH 4/4] nbd: add a nbd-control interface

[Greg KH <gregkh@...1299...>]

On Thu, Jan 26, 2017 at 12:40:47AM -0800, Christoph Hellwig wrote:
> On Wed, Jan 25, 2017 at 03:36:20PM -0600, Eric Blake wrote:
> > How do you get an fd to existing nbd block device?  Your intent is to
> > use an ioctl to request creating/opening a new nbd device that no one
> > else is using; opening an existing device in order to send that ioctl
> > may have negative ramifications to the actual user of that existing
> > device, if not permissions issues that prevent the open from even
> > happening.  Having a separate control fd makes it obvious that you are
> > asking for a new nbd device, and don't want to stomp on any existing
> > devices.
> 
> Yes, - this whole concept of needing a device first to then associate
> it with a backing store is something we had a in a lot of drivers,
> and it's always been a major problem.  Thus we've been slowly moving
> all the drivers off it.

Ok, but do you feel the "loop method" of using a char device node to
create/control these devices is a good model to follow for new devices
like ndb?

thanks,

greg k-h