b4

A guide for b4, a tool used to apply and send Linux kernel patch series through mailing lists.

In plain words
What is it for?
Applying patches from lore, preparing and sending revisions, managing cover letters and changelogs, collecting recipients, and safely working with stg.
Why use it?
It explains the workflow and warns about commands that can interfere with stg, a Git patch-stack tool, or hide patches from b4.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/chucklever/cel-kdev/b4
Any agent
npx skills add chucklever/cel-kdev --skill b4
Clone the repo
git clone --depth 1 https://github.com/chucklever/cel-kdev

Made for: Claude Code, Codex.

Per session 99 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,323 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00099 $0.03323
Opus 5 $0.00049 $0.01662
Sonnet 5 $0.00020 $0.00665
Haiku 4.5 $0.00010 $0.00332

Measured yesterday against content hash b82738574103, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

b4 scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugin/cel-kdev/skills/b4/SKILL.md · 314 lines

How it starts

The opening of the file, as written. The whole thing — 314 lines — stays where its author put it; the contents beside it link to each section on GitHub.

b4 for kernel patch workflows

CRITICAL: stg interaction hazards

These b4 operations corrupt the stg stack. Never use them when stg is active on the branch.

Prohibited Why Replacement
b4 am <msgid> Runs git am, which moves HEAD behind stg's back b4 am -l -o /tmp/series.mbx <msgid> then stg import -M /tmp/series.mbx; a maintainer intake adds a step between the two (see "Applying patches from lore")
b4 trailers -u Rebases commits to insert collected tags, breaking stg metadata Avoid; run stg repair immediately after if unavoidable

Check whether stg is active before choosing a command path. See the stg skill for the two-step activation check.

What b4 sees

b4 discovers the series as commits between the enrolled fork-point and HEAD:

fork-point (e.g., origin/master)
  |
  + patch-a          <- applied stg patch, visible to b4
  + patch-b          <- applied stg patch, visible to b4
  > patch-c          <- HEAD, visible to b4
  - patch-d          <- unapplied, in refs/stacks/ only
  - patch-e          <- unapplied, NOT visible to b4
                        => stg push -a before b4 send

Unapplied patches exist only in stg metadata and are invisible to b4. Apply all patches with stg push -a before running b4 send or b4 prep --format-patch.

Applying patches from lore

Task Command
Apply a series by message-id b4 am <msgid>
Apply a series, write mbox only b4 am -o <dir> <msgid>
Apply as stg patches b4 am -l -o /tmp/series.mbx <msgid> then stg import -M /tmp/series.mbx
Cherry-pick specific patches (1-indexed, comma-separated, ranges ok) b4 am -P 1-2,4 <msgid>
Show series diff between versions b4 diff <msgid>
Retrieve thread as mbox b4 mbox <msgid>

The stg-import row is two steps, but a maintainer intake interposes a third between them. Read "The maintainer intake edit" below before importing.

<msgid> can be a Message-Id, a lore URL, or a lore search query.

Read the full file on GitHub · 314 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 314 lines · 99 tokens per session scan A b82738574103

Subscribe to this mod's changes

b4 is a skill published in the GitHub repository chucklever/cel-kdev (2 stars, last pushed 4d ago), licensed MIT. It adds 99 tokens to every session and 3,323 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Related

Other skills, from other repositories

systematic-debugging

Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes.

obra/superpowers · 21 tokens

next-cache-components-adoption

Turn on Cache Components in a Next.js app and resolve the blocking routes it surfaces. Use when the user wants to enable, adopt, or migrate to Cache Components, flip the cacheComponents flag, work through a flood of blocking-prerender / instant validation errors, run the cache-components-instant-false codemod, or…

vercel/next.js · 95 tokens

babysit-pr

Babysit a GitHub pull request after creation by continuously polling review comments, CI checks/workflow runs, and mergeability state until the PR is merged/closed or user help is required. Diagnose failures, retry likely flaky failures up to 3 times, auto-fix/push branch-related issues when appropriate, and keep…

openai/codex · 114 tokens

imagegen

Generate or edit raster images when the task benefits from AI-created bitmap visuals such as photos, illustrations, textures, sprites, mockups, or transparent-background cutouts. Use when Codex should create a brand-new image, transform an existing image, or derive visual variants from references, and the output…

openai/codex · 113 tokens

cpu-profile-analysis

Analyze V8/Chrome CPU profiles (.cpuprofile) and DevTools trace files (Trace-.json). Use when: profiling performance, investigating slow functions, comparing code paths, finding bottlenecks, analyzing timeToRequest, understanding call trees from sampling profiler data, analyzing layout/paint/rendering, investigating…

microsoft/vscode · 71 tokens

next-cache-components-optimizer

Drive a Next.js route to instant navigation by setting up an agentic loop, under Cache Components / PPR, on initial load (hard navigation) and client-side navigation (soft navigation). Encode the goal as a failing @next/playwright instant() e2e and work it to green, one verified route at a time; the shipped test then…

vercel/next.js · 170 tokens