On Thu, Aug 27, 2015 at 3:30 PM, David Miller [off-list ref] wrote:

I don't like this.

The situation is that some sophisticated qdiscs can function without
explicit parameters, some cannot.

This is exactly what this patch tries to solve... I already mark those
with a DEFAULTABLE flag.

That is the problem you need to solve.  For example, if "opts" is NULL
HTB should use a reasonable set of defaults instead of failing.

Furthermore, you can improve the behavior when this happens.

When qdisc_create_dflt() returns NULL because ops->init() fails, do
something reasonable.

I'm not applying this patch series, it papers over the issue rather
than actually addressing it properly.

I wish I never mention that crash, which leads you to think I am trying
to fix a crash rather than a more important issue, usability. See below.

Forget about the crash, consider the current behavior:

# echo htb > default_qdisc
# succeed without any error
(then add a root qdisc and remove it)
# failure shown here in dmesg


And compare it with the behavior after my patch:

# echo htb > default_qdisc
Invalid arguments

I think this is clearly an improvement.

Thanks.