blkpath

Resolve the underlying block device path from a file path or file descriptor.

Overview

This crate provides a reliable way to determine which block device underlies a given file or directory. It uses a multi-step resolution strategy:

1. First, it uses the stat system call to get the device ID (major:minor numbers)
2. Then, it looks up the device path via /sys/dev/block/{major}:{minor}
3. If that fails, it falls back to parsing /proc/self/mountinfo

Installation

Add blkpath to your Cargo.toml:

[dependencies]
blkpath = "0.1"

Or install the CLI tool:

cargo install blkpath

Usage

Library Usage

Use the ResolveDevice trait to resolve device paths from Path or File:

use blkpath::ResolveDevice;
use std::path::Path;

fn main() -> Result<(), blkpath::DeviceResolveError> {
    let path = Path::new("/home");
    let device = path.resolve_device()?;
    println!("Device: {}", device.display());
    Ok(())
}

You can also use it with file descriptors:

use blkpath::ResolveDevice;
use std::fs::File;

fn main() -> Result<(), blkpath::DeviceResolveError> {
    let file = File::open("/home")?;
    let device = file.resolve_device()?;
    println!("Device: {}", device.display());
    Ok(())
}

Or use the convenience functions:

use blkpath::{resolve_device, resolve_device_from_file};
use std::path::Path;
use std::fs::File;

fn main() -> Result<(), blkpath::DeviceResolveError> {
    // From path
    let device = resolve_device(Path::new("/home"))?;
    println!("Device: {}", device.display());

    // From file
    let file = File::open("/home")?;
    let device = resolve_device_from_file(&file)?;
    println!("Device: {}", device.display());

    Ok(())
}

CLI Usage

# Get the block device for a path
blkpath /home
# Output: /dev/sda1

# Get help
blkpath --help

How It Works

The resolution process works as follows:

1. Stat the file/path: Get the device ID (major:minor numbers) from file metadata
2. Sysfs lookup: Check /sys/dev/block/{major}:{minor} for the device symlink
3. Mountinfo fallback: If sysfs fails, parse /proc/self/mountinfo to find the mount source

This multi-step approach ensures reliability across different Linux configurations and container environments.

Requirements

• Linux operating system
• Access to /sys/dev/block/ or /proc/self/mountinfo