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0 pointsjusticezyx4y ago0 comments

I need to double verify when was the bounded loop patch got into the kernel, I suppose it's 5.6 as you mentioned above.

What I actually was thinking is that one can write C code and ask the compiler to unroll it.

``` pragma(unroll) for (..., i < 100; ++I) { parsing code } ```

Also the other comment note the stake bookkeeping for HTTP to maintain the state when the parsing spans multiple packets, assuming here we are talking about XDP probes.

One quick idea is to use BPF_TABLE(, uint128_t, some data structure) I haven't tested if uint128_t is OK as key type. And the data structure in the value needs more thoughts. Roughly I am thinking turn any state bookkeeping into some BPF tables, and keyed through whatever data that matches the context. This probably means uint128_t as Ipve/6 address, and a nested map with key as the port. Or combined v4 IP & port.

It'll be interesting. I suppose the code from Isovalent will eventually be open sourced. Or is it already so? Haven't checked yet.

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tptacek4y ago

Bounded loops are 5.3. I'm just saying that after like 9 months of development following their introduction, it remained tricky to get the verifier to accept loops with seemingly obvious bounds. I know the feature works (I did ultimately get some loops working!) but I could not have straightforwardly ported userland C code to do it.

You've always been able to unroll loops, but of course you're chewing up code space doing that.

I don't know what BPF_TABLE is (I think it's a BCC-ism?) but BPF hash maps can take 16 byte keys. But notice that you're now writing something that looks nothing at all like Node's HTTP parser.

I'm not doubting that they did this work. I just want to know what it ends up looking like!

justicezyxOP4y ago

Oh nice, we haven't tried bounded loop, because our product is committed to support as old as 4.13.

BPF_TABLE is BCC.

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