On Wed, May 25, 2022 at 01:02:33PM -0400, Kent Overstreet wrote:

On Sat, May 21, 2022 at 12:45:59PM -0700, Stephen Hemminger wrote:

quoted

On Sat, 21 May 2022 12:45:46 -0400
Kent Overstreet [off-list ref] wrote:

quoted

On Fri, May 20, 2022 at 10:31:02PM +0200, Andrew Lunn wrote:

quoted

quoted

I want to circulate this and get some comments and feedback, and if
no one raises any serious objections - I'd love to get collaborators
to work on this with me. Flame away!  

Hi Kent

I doubt you will get much interest from netdev. netdev already
considers ioctl as legacy, and mostly uses netlink and a message
passing structure, which is easy to extend in a backwards compatible
manor.  

The more I look at netlink the more I wonder what on earth it's targeted at or
was trying to solve. It must exist for a reason, but I've written a few ioctls
myself and I can't fathom a situation where I'd actually want any of the stuff
netlink provides.

Netlink was built for networking operations, you want to set something like a route with a large
number of varying parameters in one transaction. And you don't want to have to invent
a new system call every time a new option is added.

Also, you want to monitor changes and see these events for a userspace control
application such as a routing daemon.

That makes sense - perhaps the new mount API could've been done as a netlink
interface :)

But perhaps it makes sense to have both - netlink for the big complicated
stateful operations, ioctl v2 for the simpler ones. I haven't looked at netlink
usage at all, but most of the filesystem ioctls I've looked at fall into the the
simple bucket, for me.

In RDMA, we solved this thing (standard entry points, multiple
parameters and vendor specific data) by combining netlink and ioctls.

The entry point is done with ioctls (mainly performance reason, but not
only) while data is passed in netlink attributes style.

ib_uverbs_ioctl:
https://elixir.bootlin.com/linux/v5.18/source/drivers/infiniband/core/uverbs_ioctl.c#L605

Latest example of newly added global to whole stack command:
RDMA/uverbs: Add uverbs command for dma-buf based MR registration
https://lore.kernel.org/linux-rdma/1608067636-98073-4-git-send-email-jianxin.xiong@intel.com/ (local)

Thanks