Re: [LSF/MM/BPF TOPIC] are we going to use ioctls forever?

[Matthew Wilcox <willy@infradead.org>]

On Mon, Jan 31, 2022 at 05:33:29PM -0800, Luis Chamberlain wrote:
> It would seem we keep tacking on things with ioctls for the block
> layer and filesystems. Even for new trendy things like io_uring [0].

I think the problem is that it's a huge effort to add a new syscall.
You have to get it into each architecture.  Having a single place to
add a new syscall would help reduce the number of places we use
multiplexor syscalls like ioctl().

> For a few years I have found this odd, and have slowly started
> asking folks why we don't consider alternatives like a generic
> netlink family. I've at least been told that this is desirable
> but no one has worked on it.

I don't know that I agree that "generic netlink" is desirable.
I'd like to know more about the pros and cons of this idea.

> Possible issues? Kernels without CONFIG_NET. Is that a deal breaker?
> We already have a few filesystems with their own generic netlink
> families, so not sure if this is a good argument against this.
> 
> mcgrof@fulton ~/linux-next (git::master)$ git grep genl_register_family fs
> fs/cifs/netlink.c:      ret = genl_register_family(&cifs_genl_family);
> fs/dlm/netlink.c:       return genl_register_family(&family);
> fs/ksmbd/transport_ipc.c:       ret = genl_register_family(&ksmbd_genl_family);
> fs/quota/netlink.c:     if (genl_register_family(&quota_genl_family) != 0)

I'm not sure these are good arguments in favour ... other than quota,
these are all network filesystems, which aren't much use without
CONFIG_NET.

> mcgrof@fulton ~/linux-next (git::master)$ git grep genl_register_family drivers/block
> drivers/block/nbd.c:    if (genl_register_family(&nbd_genl_family)) {

The, er, _network_ block device, right?