alessandrocarminati / -systemd_add_lun

This systemd add-in for Buildroot optimizes boot times in systems by selectively scanning a specified LUN within a SCSI chain, bypassing the default comprehensive scan.

systemd Add-in for Buildroot

Introduction

This project aims to optimize the boot time within a system by providing a systemd add-in for Buildroot. The specific focus of this module is to enumerate a particular LUN within a SCSI chain containing multiple devices. By leveraging systemd capabilities and configuring the kernel arguments appropriately, this module efficiently scans the intended LUN, reducing boot time by avoiding unnecessary device scans.

Purpose

In systems, especially embedded environments utilizing Buildroot, optimizing boot time is critical for efficient operation. Default method involve the Linux kernel scanning all devices within a SCSI chain during boot, which can lead to significant delays. This project addresses this issue by introducing a systemd add-in that intelligently scans only the intended LUN, leaving other devices for later enumeration.

Functionality

The key functionalities of this systemd add-in include:

• Enumerating a specific LUN within a SCSI chain.
• Utilizing the scsi_mod.scan=manual kernel argument to prevent automatic scanning of all devices in the chain.
• Use fake kernel arguments (host2scan, channel2scan, target2scan, lun2scan) to specify the controller, channel, target, and intended LUN for scanning.

Usage

To use this systemd add-in effectively, follow these steps:

• Ensure that the scsi_mod.scan=manual kernel argument is used to prevent the kernel from scanning all devices in the SCSI chain.
• Pass the following fake kernel arguments:
  • host2scan: Specify the controller where the scan will be performed.
  • channel2scan: Specify the channel for scanning.
  • target2scan: Specify the SCSI target for scanning.
  • lun2scan: Specify the intended LUN for scanning.
• Integrate the provided systemd add-in into your Buildroot project.
• Configure systemd to execute the add-in during boot.
• Use init.sh to initialize the two buildroot packages

Directories

The project contain two directories:

• systemd_add_lun is the prototype directory where the actual scan is performed by a bash script
• systemd_add_lun_q is the directory containing the c version of the script for quicker activation.