Crate duende_ublk 

duende-ublk - ublk device lifecycle management

This crate provides tools for managing ublk (userspace block device) lifecycle, particularly for swap-critical daemons that need to clean up orphaned devices.

Problem: Orphaned ublk Devices

When a ublk daemon crashes or is killed, the kernel may retain device state even after the /dev/ublkbN block device disappears. This causes:

• “File exists” errors when creating new devices
• Device ID conflicts
• System requires reboot to clear stale state

Solution

use duende_ublk::{UblkControl, cleanup_orphaned_devices};

fn main() -> Result<(), duende_ublk::Error> {
    // Clean up any orphaned devices from previous crashes
    let cleaned = cleanup_orphaned_devices()?;
    println!("Cleaned {} orphaned devices", cleaned);

    // Now safe to create new devices
    Ok(())
}

Kernel Interface

This crate uses io_uring URING_CMD to communicate with the ublk kernel driver. Linux 6.0+ is required.

Structs

UblkControl

ublk control device handle

UblkCtrlCmd

Control command payload (32 bytes) - matches kernel ublksrv_ctrl_cmd

UblkCtrlCmdExt

Extended control command for io_uring 128-byte SQE (80 bytes total)

UblkCtrlDevInfo

Device info structure (64 bytes) - matches kernel ublksrv_ctrl_dev_info

Enums

Error

Errors that can occur during ublk operations

Constants

UBLK_CTRL_DEV

Path to ublk control device

Functions

block_device_exists

Check if a block device exists for a given device ID.

block_device_path

Build the block device path for a device ID.

build_device_command

Build a command structure for a device operation.

build_get_info_command

Build a command structure for getting device info.

char_device_path

Build the character device path for a device ID.

cleanup_orphaned_devices

Clean up all orphaned ublk devices

control_device_available

Check if the ublk control device is available.

detect_orphaned_devices

Detect orphaned ublk devices

detect_orphans_in_dir

Detect orphaned devices in a given directory (for testing).

interpret_command_result

Interpret a command result code.

parse_char_device_id

Parse a ublk character device name to extract the device ID.