Set attach type during load for BPF_PROG_TYPE_CGROUP_SKB

[nak3]

As per title, this patch sets expected_attach_type during load.

Fix #262

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[dave-tucker]

@nak3 Thanks for the PR!

Does the current behaviour cause an issue (other than misleading strace output)?
Since CgroupSkb programs can be attached in either direction, and you have to provide a direction on attach anyway,, I guess this change is just cosmetic?

I'm not against the change at all... I just want to understand the motivation.

[alessandrod]

this should use map()

[nak3]

Thank you! updated.

[nak3]

Hi @dave-tucker

Yes, one very small issue is caused. (Sorry I should explain it in the linked issue.)
As Kernel code allows only Egress to use the return values (2 or 3), currently attach type "Egress" causes the following error:

#[cgroup_skb(name="cgroup_skb_tmp", attach="egress")]
pub fn cgroup_skb_tmp(ctx: SkBuffContext) -> i32 {
    3
}

this (return 3) causes the following error:

Error: the BPF_PROG_LOAD syscall failed. Verifier output: func#0 @0
0: R1=ctx(id=0,off=0,imm=0) R10=fp0
0: (b7) r0 = 3                        ; R0_w=inv3
1: (95) exit
At program exit the register R0 has value (0x3; 0x0) should have been in (0x0; 0x1)
verification time 10 usec
stack depth 0
processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0


Caused by:
    Invalid argument (os error 22)

After applied this patch, the return value 2 or 3 for Egress is allowed.