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

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jan 25, 2017 at 06:25:11PM +0000, Alex Bligh wrote:
> 
> > On 25 Jan 2017, at 16:48, Alex Gartrell <agartrell@fb.com> wrote:
> > 
> > 
> > If nbd were *all* netlink I think that that'd be fine, but you'd have
> > problems implementing the NBD_DOIT function in that fashion.  So I'd
> > rather stick to the char device ioctl thing because it's more
> > consistent with the old NBD stuff as well as the loop device stuff.
> 
> I spend most of my time looking at the userspace side of NBD so
> apologies if this is off base.
> 
> Given (because of NBD_DO_IT) we need an ioctl anyway, and we have
> an ioctl that isn't going to go away, it would seem better if possible
> to stick with ioctls, and not introduce either a dependency
> on netlink (which would presumably bloat static binaries that
> are used early in the boot process). Personally I'd have thought
> adding a new NBD ioctl (or extending an existing one) would be
> less entropy than adding a new char device.

Why can't you just do this on any existing nbd block device with an
ioctl to it?  No need to have to do it on an out-of-band char device
node, right?

thanks,

greg k-h