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

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

On Mon, Jan 23, 2017 at 09:57:52AM -0500, Josef Bacik wrote:
> On Mon, Jan 23, 2017 at 9:52 AM, Greg KH <gregkh@...1299...> wrote:
> > On Mon, Jan 23, 2017 at 09:42:08AM -0500, Josef Bacik wrote:
> > > 
> > > 
> > >  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,
> > 
> > Again, please don't duplicate what loop did, we must _learn_ from
> > history, not repeat it :(
> 
> Sure but what am I supposed to do?  Have some random sysfs knobs?  Thanks,

It all depends on what you are trying to do.  I have yet to figure that
out at all here :(