iovisor/bcc

helper for memmem()

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#471 opened on Mar 31, 2016

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enhancementhelp wantedprio:medium

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Description

Protocol such as DNS or IPv6 are hard to filter with cBPF because important parts are relative to floating offset, since BPF disallows loops and has relatively narrow registers, we have to unroll them and scan message with a lot of branches, burning the instruction limit.

Proposal

Provide kernel helper such as memmem(off_from, off_to, pattern) where offsets (R0, R1) are relative to packet payload, and pattern (R2) is a b/h/w/dw, and returned value would be offset in packet where the match occured or packet length (no occurence).

Contributor guide

Research direction
Study existing BPF kernel helpers (e.g., bpf skb load bytes) and kernel memory scanning functions. Design a memmem helper that takes relative offsets and a pattern, returns offset or packet length. Implement in kernel/bpf/helpers.c and expose via bpf helper defs.h.
Tech stack
c
Domain
networking
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
CBPF programmingLinux kernel internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30