datapath: Introduce helpers for __ctx_is checks

[brb]

In the datapath we have a few __ctx_is checks:

> git grep '__ctx_is =='
bpf/include/bpf/ctx/common.h:    return __ctx_is == __ctx_xdp;
bpf/include/bpf/helpers.h:#if __ctx_is == __ctx_skb
bpf/lib/edt.h:#if defined(ENABLE_BANDWIDTH_MANAGER) && __ctx_is == __ctx_skb
bpf/lib/identity.h:#if __ctx_is == __ctx_skb
bpf/lib/identity.h:#endif /* __ctx_is == __ctx_skb */
bpf/lib/nodeport.h:#if __ctx_is == __ctx_skb
bpf/lib/overloadable.h:#if __ctx_is == __ctx_skb
bpf/lib/pcap.h:# define capture_enabled (__ctx_is == __ctx_xdp)
bpf/lib/proxy.h:#if !(__ctx_is == __ctx_skb)
bpf/lib/qm.h:#if defined(RESET_QUEUES) && __ctx_is == __ctx_skb

For the sake of readability, we should introduce ctx_is_{skb,xdp}() helpers, and replace the ifdef's with the if statements.

[SamrathPalSingh]

/assign

[brb]

@SamrathPalSingh Are you still interested in working on this issue?

[spacewander]

Hi @brb, I am interested in it.

For the sake of readability, we should introduce ctx_is_{skb,xdp}() helpers, and replace the ifdef's with the if statements.

Do you mean ctx_is_skb macro? There is a guard macro in

cilium/bpf/include/bpf/helpers.h

Lines 27 to 31 in ac326f8

	#if __ctx_is == __ctx_skb
	# include "helpers_skb.h"
	#else
	# include "helpers_xdp.h"
	#endif

A runtime if with function call may not support including different files.

[brb]

Hi @spacewander . I meant the following:

bool ctx_is_skb() {
    return __ctx_is == __ctx_skb
}

And then replace #if __ctx_is == __ctx_skb with if ctx_is_skb() { .... Same goes for the XDP.

[spacewander]

Yes. But this doesn't allow selecting #include <file> dynamically, as shown in #23008 (comment).
Do we need to keep that pattern unchanged?

[brb]

Do we need to keep that pattern unchanged?

Ah, I see. Yep, let's keep it unchanged.