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Linux Pass-Through Driver and Process Signal Handling

IP.com Disclosure Number: IPCOM000031509D
Original Publication Date: 2004-Sep-27
Included in the Prior Art Database: 2004-Sep-27
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Abstract

Since the Linux SCSI generic (sg) driver does not provide the SCSI reserve and the SCSI release functions, it will cause data integrity problem for its applications in the Storage Area Network (SAN) environment. The Tivoli Storage Management (TSM) supports the SCSI reserve and the SCSI release functions in its Linux pass-through driver. The TSM Linux pass-through driver can monitor some system signals such as SIGILL, SIGABRT and so on. Once trapping one of these system signals, the TSM Linux pass-through driver will release the SCSI devices which were reserved early. This signal monitoring function guarantees the SCSI devices can be released before the system crash occurs. Therefore, adding the SCSI reserve and the SCSI release functions can guarantee no data integrity problem will happen and devices can be released all the time.

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Linux Pass-Through Driver and Process Signal Handling

1. Introduction:

In general, most SCSI generic drivers in operating systems provide mechanisms to reserve and release devices for SCSI generic driver applications. This mechanism is very important for the SCSI generic driver application on storage area network (SAN) environments.

The Linux SCSI generic (sg) driver in the Linux operating system does not provide reserve/release mechanism for its applications. If there is no such reserve/release mechanism in the Linux SCSI generic driver, it will cause problems for the SCSI generic driver applications running on SAN environments.

There are three major problems.

First, if no reserve function, the SCSI generic driver will allow all of its applications from different hosts to control the same storage device on a SAN environment simultaneously. Under this condition, data on the storage device can be lost or damaged since permitting the storage device to be accessed by different applications from different hosts on the same SAN environment at the same time can result in data being overwritten or deleted.

Second, if no release function, the SCSI generic driver will not release the storage devices reserved by its applications when these applications hang, abort or crash. Under this circumstance, all reserved storage devices on the SAN environment will be locked and not allow those applications from different hosts on the same SAN access until someone does power off/on for these reserved devices. This situation limits the maximum device usage on the SAN and loses the ability to easily control devices in the SAN environment.

Third, the failover mechanism is not supported by all of the SCSI tape devices. Hence the failover mechanism cannot help to overcome the above drawbacks of the Linux SCSI generic driver running on SCSI tape devices in a SAN environment.

2. Approach:

Major Ideas:

Adding reserve/release device mechanisms to the SCSI generic driver applications.

Tracking the signal of the application's process running on the Linux operating system.

Releasing reserved devices trapping a signal like SIGILL or SIGABRT.

Implementation:

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The Tivoli Storage Management (TSM) server is one of applications of the Linux SCSI generic driver. The TSM pass-through driver is a part of the TSM server and is embedded in the TSM server. The TSM pass-through driver receives device usage requests from the TSM server, builds corresponding SCSI commands and then sends these commands to the Linux SCSI generic driver. The TSM pass-through driver is running in kernel user space and can control SCSI tape devices on the SAN environment via the Linux SCSI generic driver.

Before using a SCSI device, the TSM pass-through driver sends this command via the Linux SCSI generic driver to the SCSI device to reserve this SCSI devic...