Agent skill

Writing Char Drivers

by mohitmishra786 in mohitmishra786/low-level-dev-skills

Character driver skill for Linux kernel char devices. An agent skill from mohitmishra786/low-level-dev-skills.

MITAuto-check passedDevelopment

Install Writing Char Drivers

skills CLI

$ npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install mohitmishra786/low-level-dev-skills writing-char-drivers --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/mohitmishra786/low-level-dev-skills.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/kernel-dev/writing-char-drivers .claude/skills/writing-char-drivers && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "writing-char-drivers" agent skill from https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers into .claude/skills/writing-char-drivers/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-char-drivers", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install mohitmishra786/low-level-dev-skills writing-char-drivers --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/mohitmishra786/low-level-dev-skills.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/kernel-dev/writing-char-drivers .agents/skills/writing-char-drivers && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "writing-char-drivers" agent skill from https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers into .agents/skills/writing-char-drivers/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-char-drivers", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install mohitmishra786/low-level-dev-skills writing-char-drivers --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/mohitmishra786/low-level-dev-skills.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/kernel-dev/writing-char-drivers .cursor/skills/writing-char-drivers && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "writing-char-drivers" agent skill from https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers into .cursor/skills/writing-char-drivers/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-char-drivers", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/mohitmishra786/low-level-dev-skills.git --path skills/kernel-dev/writing-char-drivers

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install mohitmishra786/low-level-dev-skills writing-char-drivers --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/mohitmishra786/low-level-dev-skills.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/kernel-dev/writing-char-drivers .gemini/skills/writing-char-drivers && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "writing-char-drivers" agent skill from https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers into .gemini/skills/writing-char-drivers/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-char-drivers", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install mohitmishra786/low-level-dev-skills writing-char-drivers

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/mohitmishra786/low-level-dev-skills.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/kernel-dev/writing-char-drivers .github/skills/writing-char-drivers && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "writing-char-drivers" agent skill from https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers into .github/skills/writing-char-drivers/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-char-drivers", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install mohitmishra786/low-level-dev-skills writing-char-drivers --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/mohitmishra786/low-level-dev-skills.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/kernel-dev/writing-char-drivers .opencode/skills/writing-char-drivers && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "writing-char-drivers" agent skill from https://github.com/mohitmishra786/low-level-dev-skills/tree/main/skills/kernel-dev/writing-char-drivers into .opencode/skills/writing-char-drivers/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "writing-char-drivers", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: writing-char-drivers
GitHub stars: 252
Token cost: ~1.1k tokens
SKILL.md length: 184 words
Files: 1
Skills in repo: 138
Repo updated: Jun 27, 2026
First seen: Oct 7, 2026
Licence: MIT

At a glance

Character driver skill for Linux kernel char devices. An agent skill from mohitmishra786/low-level-dev-skills.

Works in 6 steps: Char device registration → Safe userspace I/O → ioctl pattern → …
Implementing fileoperations
SKILL.md covers Purpose, When to Use, Workflow and Common Problems, plus 1 more section
Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md

What it does

Writing Char Drivers is an agent skill from mohitmishra786/low-level-dev-skills. Character driver skill for Linux kernel char devices. Use when implementing fileoperations, cdev, copytouser, ioctl, or mmap for userspace interfaces. Activates on queries about char device, cdev, fileoperations, copyfromuser, ioctl, or kernel mmap.

Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development. It works with Linux. The repository describes itself as: A curated suite of AI agent skills for systems and low-level programming with C/C++, Rust, and Zig toolchains, covering compilers, debuggers, profilers, build systems…. The licence is MIT.

When your agent uses it

Implementing fileoperations
Mmap for userspace interfaces

Example prompts

“/writing-char-drivers”

Workflow steps

6 steps, taken from the step headings in SKILL.md.

Char device registration
Safe userspace I/O
ioctl pattern
mmap (device memory)
poll / async I/O
Agent usage

What it can do on your machine

Read from SKILL.md and the folder at commit bdc5847. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md (its code samples are c).
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Writing Char Drivers loads about 1.1k tokens when it runs. Until then it costs about 69 tokens; SKILL.md has 184 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~69
When it runs · the whole SKILL.md, loaded when a task matches: ~1.1k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from mohitmishra786/low-level-dev-skills at commit bdc5847, republished under its MIT licence (© mohitmishra786). 184 words, ~1,075 tokens.

Download SKILL.mdSave it as .claude/skills/writing-char-drivers/SKILL.md (or your agent's skills folder).

name: writing-char-drivers
description: Character driver skill for Linux kernel char devices. Use when implementing file_operations, cdev, copy_to_user, ioctl, or mmap for userspace interfaces. Activates on queries about char device, cdev, file_operations, copy_from_user, ioctl, or kernel mmap.

Writing Character Drivers

Purpose

Guide agents through Linux character device implementation: struct file_operations, cdev registration, safe userspace copies, ioctl design, and basic mmap — focused depth beyond skills/kernel/device-drivers.

When to Use

Exposing hardware to /dev/mydev
Implementing read/write/poll from kernel
Defining ioctl commands with type-safe macros
Mapping device MMIO to userspace (carefully)

Workflow

1. Char device registration

#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>

#define MY_MAJOR 0   /* 0 = dynamic alloc */
#define MY_MINOR 0

static dev_t devno;
static struct cdev my_cdev;
static struct class *class;

static const struct file_operations my_fops = {
    .owner          = THIS_MODULE,
    .open           = my_open,
    .release        = my_release,
    .read           = my_read,
    .write          = my_write,
    .unlocked_ioctl = my_ioctl,
    .llseek         = no_llseek,
};

static int __init my_init(void)
{
    int ret = alloc_chrdev_region(&devno, MY_MINOR, 1, "mydev");
    if (ret)
        return ret;

    cdev_init(&my_cdev, &my_fops);
    ret = cdev_add(&my_cdev, devno, 1);
    if (ret)
        goto err_cdev;

    class = class_create("mydev");
    device_create(class, NULL, devno, NULL, "mydev");
    return 0;

err_cdev:
    unregister_chrdev_region(devno, 1);
    return ret;
}

Modern drivers often use devm_* variants inside probe.

2. Safe userspace I/O

static ssize_t my_read(struct file *filp, char __user *buf,
                       size_t count, loff_t *ppos)
{
    char kbuf[128];
    ssize_t len;

    if (*ppos >= sizeof(kbuf))
        return 0;
    len = min(count, sizeof(kbuf) - *ppos);
    memcpy(kbuf, "data", 4);
    if (copy_to_user(buf, kbuf + *ppos, len))
        return -EFAULT;
    *ppos += len;
    return len;
}

Never dereference __user pointers directly.

3. ioctl pattern

#include <linux/ioctl.h>

#define MY_IOC_MAGIC 'k'
#define MY_IOC_RESET  _IO(MY_IOC_MAGIC, 0)
#define MY_IOC_SET    _IOW(MY_IOC_MAGIC, 1, int)

static long my_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
    switch (cmd) {
    case MY_IOC_RESET:
        return 0;
    case MY_IOC_SET: {
        int val;
        if (copy_from_user(&val, (void __user *)arg, sizeof(val)))
            return -EFAULT;
        return 0;
    }
    default:
        return -ENOTTY;
    }
}

Use _IOWR with fixed-size structs; prefer compat_ioctl on bi-arch.

4. mmap (device memory)

static int my_mmap(struct file *filp, struct vm_area_struct *vma)
{
    unsigned long size = vma->vm_end - vma->vm_start;
    phys_addr_t phys = device_phys_base;

    vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
    return remap_pfn_range(vma, vma->vm_start, phys >> PAGE_SHIFT,
                           size, vma->vm_page_prot);
}

Prefer mmap of DMA buffers only with explicit size limits and permission checks.

5. poll / async I/O

Implement poll + wake_up_interruptible for blocking reads; use fasync_helper for SIGIO.

6. Agent usage

/writing-char-drivers Add unlocked_ioctl SET_SPEED to existing platform driver

Common Problems

Symptom	Cause	Fix
`-EFAULT`	Bad user pointer	Validate `access_ok` (older) / rely on `copy_*`
`ENOTTY`	Wrong ioctl magic	Match userspace `ioctl.h`
Major conflict	Static major taken	Use `alloc_chrdev_region`
mmap SIGSEGV	Cached mapping to device	`pgprot_noncached`
Sleep in ioctl	Holding spinlock	Drop lock before blocking

skills/kernel-dev/platform-device-model — probe context
skills/kernel/device-drivers — full driver lifecycle
skills/kernel/kernel-concurrency — locking in file ops
skills/kernel-dev/kernel-debugging-advanced — trace ioctl path
skills/low-level-programming/linux-kernel-modules — module boilerplate

Files

Just SKILL.md in skills/kernel-dev/writing-char-drivers of mohitmishra786/low-level-dev-skills.

Open the folder on GitHubat commit bdc5847

Compare with similar skills

Writing Char Drivers next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Writing Char Drivers compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Writing Char Drivers this skillmohitmishra786/low-level-dev-skills	252	—	~1.1k	Automated safety check: Pass	MIT	3 mo ago
Update .NET OS Packagesdotnet/core	22k	—	~2.3k	Automated safety check: Pass	MIT	2 days ago
Cut Releasejfernandez/bpftop	2.7k	—	~2k	Automated safety check: Pass	Apache-2.0	1 mo ago
Native Feel Cross Platform Desktopyetone/native-feel-skill	1.9k	1 repos	~1.5k	Automated safety check: Pass	MIT	4 mo ago
PlotJuggler 4 Perf ProfilingPlotJuggler/PlotJuggler	6.2k	—	~1.6k	Automated safety check: Notes	MPL-2.0	10 days ago
ONNX Runtime Source Buildmicrosoft/onnxruntime	22k	—	~1.4k	Automated safety check: Pass	MIT	today

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Questions about Writing Char Drivers

What does Writing Char Drivers do?

Character driver skill for Linux kernel char devices. An agent skill from mohitmishra786/low-level-dev-skills. Writing Char Drivers is an agent skill from mohitmishra786/low-level-dev-skills. Character driver skill for Linux kernel char devices.

When should I use Writing Char Drivers?

Writing Char Drivers fits situations like: implementing fileoperations; mmap for userspace interfaces.

How do I install Writing Char Drivers in Claude Code?

Run `npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a claude-code`. Or copy the skill folder (skills/kernel-dev/writing-char-drivers in mohitmishra786/low-level-dev-skills) into .claude/skills/writing-char-drivers in your project. Claude Code loads it when a task matches its description.

How do I install Writing Char Drivers in Codex?

Run `npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a codex`. Or copy the skill folder (skills/kernel-dev/writing-char-drivers in mohitmishra786/low-level-dev-skills) into .agents/skills/writing-char-drivers in your project. Codex loads it when a task matches its description.

Can I use Writing Char Drivers in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add mohitmishra786/low-level-dev-skills --skill writing-char-drivers -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/writing-char-drivers, .gemini/skills/writing-char-drivers, .github/skills/writing-char-drivers and .opencode/skills/writing-char-drivers in your project.

What does Writing Char Drivers need to run?

SKILL.md names no scripts, command-line tools or credentials: Writing Char Drivers is instructions for the agent only.

Does Writing Char Drivers access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Writing Char Drivers safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Writing Char Drivers use?

Writing Char Drivers is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Writing Char Drivers use?

About 1.1k tokens (SKILL.md is roughly 4.3k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Writing Char Drivers?

Skills that share tags, products or a category with Writing Char Drivers: Update .NET OS Packages (dotnet/core, 22k stars), Cut Release (jfernandez/bpftop, 2.7k stars), Native Feel Cross Platform Desktop (yetone/native-feel-skill, 1.9k stars) and PlotJuggler 4 Perf Profiling (PlotJuggler/PlotJuggler, 6.2k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Writing Char Drivers?

mohitmishra786 (a GitHub user) maintains it in mohitmishra786/low-level-dev-skills, which has 252 GitHub stars. The repository holds 138 skills in this directory. The repository was last updated on June 27, 2026.

Source: mohitmishra786/low-level-dev-skills on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Writing Char Drivers

Facts

At a glance

What it does

When your agent uses it

Example prompts

Workflow steps

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Writing Character Drivers

Purpose

When to Use

Workflow

1. Char device registration

2. Safe userspace I/O

3. ioctl pattern

4. mmap (device memory)

5. poll / async I/O

6. Agent usage

Common Problems

Related Skills

Files

Compare with similar skills

Similar skills

More from mohitmishra786/low-level-dev-skills

Related

Questions about Writing Char Drivers