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

[Josef Bacik <jbacik@...2204...>]

On Sat, Jan 21, 2017 at 4:05 AM, Greg KH <gregkh@...1299...> 
wrote:
> On Fri, Jan 20, 2017 at 04:56:52PM -0500, Josef Bacik wrote:
> >  This patch mirrors the loop back device behavior with a few 
> > changes.  First
> >  there is no DEL operation as NBD doesn't get as much churn as loop 
> > devices do.
> >  Secondly the GET_NEXT operation can optionally create a new NBD 
> > device or not.
> >  Our infrastructure people want to not allow NBD to create new 
> > devices as it
> >  causes problems for them in containers.  However allow this to be 
> > optional as
> >  things like the OSS NBD client probably doesn't care and would like 
> > to just be
> >  given a device to use.
> >
> >  Signed-off-by: Josef Bacik <jbacik@...2204...>
>
> A random char device with odd ioctls?  Why?  There's no other
> configuration choice you could possibly use?  Where is the userspace
> tool that uses this new kernel api?
>
> You aren't passing in structures to the ioctl, so why does this HAVE 
> to
> be an ioctl?

Again, this is how loop does it so I assumed a known, regularly used 
API was the best bet.  I can do literally anything, but these 
interfaces have to be used by other people, including internal people.  
The /dev/whatever-control is a well established way for interacting 
with dynamic device drivers (loop, DM, btrfs), so that's what I went 
with.  Thanks,

Josef