Add support for Flow Dissector programs

[tamird]

This picks up from #802.

I've addressed comments in a separate commit to somwhat ease review; this will
be squashed before merging.

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[mergify]

Hey @alessandrod, this pull request changes the Aya Public API and requires your review.

[dave-tucker]

Reviewed 14 of 14 files at r1, 4 of 4 files at r2, all commit messages.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @alessandrod)

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aya/src/programs/flow_dissector.rs line 95 at r2 (raw file):

                .insert(FlowDissectorLink::new(FdLink::new(link_fd)))
        } else {
            todo!("support attachment via BPF_PROG_ATTACH")

rather than marking TODO, can we add the implementation here? ISTR linking to one that could be basically copy/pasted from another program type with similar attach semantics - you'd just need to change a couple of constants.

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test/integration-ebpf/src/test.rs line 51 at r2 (raw file):

#[flow_dissector]
pub fn test_flow(_ctx: FlowDissectorContext) -> u32 {
    // TODO: write an actual flow dissector. See tools/testing/selftests/bpf/progs/bpf_flow.c in the

I'm torn, I'd prefer a program here vs. a TODO.
Without a program written to exercise the aya-ebpf API it's hard to know if we have enough implemented to support a trivial example. For Aya userspace, this doesn't matter so much since you could bring a program written in C.

That said I can see value in merging what we have to encourage others to contribute or give us feedback on what's missing.

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aya-ebpf-macros/src/lib.rs line 571 at r2 (raw file):

/// pub fn dissect(_ctx: FlowDissectorContext) -> u32 {
///     // TODO: do something useful here.
///     return 0

perhaps return one of the constants described in the doc here instead?
BPF_FLOW_DISSECTOR_CONTINUE?

[tamird]

Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @alessandrod and @dave-tucker)

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aya/src/programs/flow_dissector.rs line 95 at r2 (raw file):

Previously, dave-tucker (Dave Tucker) wrote…

rather than marking TODO, can we add the implementation here? ISTR linking to one that could be basically copy/pasted from another program type with similar attach semantics - you'd just need to change a couple of constants.

Ok, done, I think.

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aya-ebpf-macros/src/lib.rs line 571 at r2 (raw file):

Previously, dave-tucker (Dave Tucker) wrote…

perhaps return one of the constants described in the doc here instead?
BPF_FLOW_DISSECTOR_CONTINUE?

Done.

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test/integration-ebpf/src/test.rs line 51 at r2 (raw file):

Previously, dave-tucker (Dave Tucker) wrote…

I'm torn, I'd prefer a program here vs. a TODO.
Without a program written to exercise the aya-ebpf API it's hard to know if we have enough implemented to support a trivial example. For Aya userspace, this doesn't matter so much since you could bring a program written in C.

That said I can see value in merging what we have to encourage others to contribute or give us feedback on what's missing.

That's basically where I am with it :/

[dave-tucker]

one small nit, but happy for this to merge either way.

Reviewable status: 8 of 14 files reviewed, 3 unresolved discussions (waiting on @alessandrod)

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aya/src/programs/flow_dissector.rs line 104 at r4 (raw file):

                netns_fd,
                BPF_FLOW_DISSECTOR,
                CgroupAttachMode::Single,

nit. This could be CgroupAttachMode::default() which I think better captures the intent - we don't actually care about the value here.

[tamird]

Reviewable status: 8 of 14 files reviewed, 2 unresolved discussions (waiting on @alessandrod and @dave-tucker)

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aya/src/programs/flow_dissector.rs line 104 at r4 (raw file):

Previously, dave-tucker (Dave Tucker) wrote…

nit. This could be CgroupAttachMode::default() which I think better captures the intent - we don't actually care about the value here.

Done!