Re: [PATCH RFC v2 1/8] xdp: Infrastructure to generalize XDP

On 2017年02月10日 10:30, Tom Herbert wrote:

On Thu, Feb 9, 2017 at 5:48 PM, David Miller [off-list ref] wrote:

quoted

From: Tom Herbert <redacted>
Date: Thu, 9 Feb 2017 15:08:22 -0800

quoted

Okay, how about this... I'll add a configuration option like
XDP_ALLOW_OTHER_HOOKS. The default will be to disallow setting any
hook other than a BPF. If it is set, then we'll accept other hooks
to be run. This way mostly restrict the interface by default, but
still allow experimentation with other hook types like I need with
TXDP or maybe the netfilter guys might want to fastpath netfilter
etc. When we we bring a working robust implementation to netdev that
show clear benefits then we can add those to BPF as the "allowed"
hooks at that time. So this strictly controls the interfaces, but
still also allows room for innovation.

Anyone is allowed to "innovate" in their own private kernel tree.

But I'm not unleashing that upstream.

The only reason I accepted XDP is entirely because it is limited
in scope to eBPF.  All eBPF programs execute in finite time,
cannot loop, cannot deadlock, cannot access arbitrary pieces
of kernel memory and datastructures.

It is a well defined, constrained, and incredibly tightly controlled
execution environment for implementing policy, monitoring and control.

And it's also incredibly invasive in the core data path of drivers.
TBH it is not clear to me that the narrow use cases for XDP justifies
adding this complexity being added to every driver.

XDP is valuable for fast userspace forwarding (e.g macvtap passthrough 
mode). I hope we can leave a window for this. Or we may need introduce 
other similar hooks.

Thanks

In any case, I withdraw the patch set.

Tom