On Mon, Jan 23, 2017 at 10:03 AM, Greg KH <gre...@linuxfoundation.org> wrote: > On Mon, Jan 23, 2017 at 09:57:52AM -0500, Josef Bacik wrote: >> On Mon, Jan 23, 2017 at 9:52 AM, Greg KH >> <gre...@linuxfoundation.org> 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 >> > > <gre...@linuxfoundation.org> 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 <jba...@fb.com> >> > > > >> > > > 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 :(
I explained it in the changelog and my response to Wouter. NBD preallocates all of its /dev/nbd# devices at modprobe time, so there's no way to add new devices as we need them. Loop accomplishes this with the /dev/loop-control and an ioctl. Then we also need a way to figure out what is the first /dev/nbd# device that isn't currently in use in order to pick the next one to configure. Keep in mind that all of the configuration for /dev/nbd# devices is done through ioctls to those devices, so having a ioctl interface for the control device is consistent with the rest of how NBD works. Thanks, Josef ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Nbd-general mailing list Nbd-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nbd-general
