Argument list too long > 10 programs (MAX_DISPATCHER_ACTIONS ?)

[Ch4rlus]

Hey,

I have 10 XDP programs loaded on a interface. Trying to load a 11th program generates :

Couldn't attach XDP program on iface 'enp3s0np0': Argument list too long(-7)

I guess this is linked to MAX_DISPATCHER_ACTIONS = 10 and the following condition:
https://github.com/xdp-project/xdp-tools/blob/abff006c6568ba84cff7d88006439506076e4add/lib/libxdp/libxdp.c#L2931C1-L2935C19

#xdp-tools/lib/libxdp/libxdp.c
	if (num_new_progs > MAX_DISPATCHER_ACTIONS)
		return ERR_PTR(-E2BIG);

	pr_debug("Generating multi-prog dispatcher for %zu programs\n",
		 num_new_progs);

May I suggest adding a debug (or error) message to indicate the limit? It would make it easier for the user to understand the error :)

On a side node: Has anyone tried increasing MAX_DISPATCHER_ACTIONS? I imagine there's a good reason for the limit to be low, but I haven't found any discussion about it.

[tohojo]

Good point about the error message - we should improve that. How are you loading the programs? Using xdp-loader, or through the libxdp API?

As for the reason for the maximum of 10 programs, well, I picked that somewhat arbitrarily when first writing that code. Didn't really expect anyone to hit the limit as there's a certain element of diminishing returns the more programs you load (performance-wise). What's you use case for loading that many programs? :)