Kernel Options for Accessing Drives

When you configure your kernel for removable devices, you might need to check in several locations for appropriate device drivers. If you configure your Linux kernel by issuing the make xconfig command in the Linux source code directory (generally /usr/src/linux), you deal with two windows, which are shown in Figure 6.3. The first is the Linux Kernel Configuration window, which lists various broad classes of drivers and configuration options, such as General setup and Block devices. The second is the window you get when you click on any of these

Chapter 6

options, such as the General setup window in Figure 6.3. It's here that you set the options for your specific removable devices, although you set options for specific devices in several different windows.

Figure 6.3

Open a specific kernel option's window, such as the General setup window, by clicking its matched button in the Linux Kernel Configuration window.

Figure 6.3

Open a specific kernel option's window, such as the General setup window, by clicking its matched button in the Linux Kernel Configuration window.

If you configure your kernel using a non-GUI tool, such as make menuconfig or make config, you make the same selections, but you use a text-based configuration tool, rather than the windows shown in Figure 6.3.

In most cases, you have a choice between three options for each device:

• Y Builds the driver into the main Linux kernel file. The driver will always be ready and available, but will also always consume at least some RAM.

• M Builds the driver as a separate module file, which you can load and unload as you see fit. This option saves RAM, but causes a slight delay when accessing files, especially if you don't configure your system to automatically load kernel modules as needed. This option isn't available for all devices, although it is for most.

• N Omits the driver from the kernel. You won't be able to use this device or feature.

Kernel Options for Floppies

Because of its simplicity, there's not much to be said about the options for floppy disks. On x86 computers, you must answer Y or M to the Normal PC floppy disk support option in the Block devices area to use the built-in floppy disk port. I generally use the modular compilation option to save a small amount of RAM, because I don't use floppies at all times.

Part II

If you have an external USB floppy, check the section on kernel options for USB devices. If you want to use an LS-120 drive to read conventional floppies, you do so through whatever interface your LS-120 drive uses.

Kernel Options for EIDE/ATAPI Drives

EIDE/ATAPI options are in the Block devices area. There are several options you might need or want to activate, in order to use an EIDE/ATAPI removable disk:

• Enhanced IDE/MFM/RLL disk/cdrom/tape/floppy support This option must be set to Y or M to use EIDE/ATAPI devices of any sort. If you boot from an EIDE hard disk, it must be set to Y. If you use a SCSI hard disk but have an EIDE removable disk, you can set it to M if you like.

• Include IDE/ATA-2 DISK support You must set this option to Y or M to use removable disks. Like the main EIDE support, this option must be Y if you boot from an EIDE hard disk, but can be either Y or M if you boot from a SCSI hard disk.

• Include IDE/ATAPI FLOPPY support You must activate this option (Y or M) to use a removable EIDE disk.

• EIDE chipset options Assorted options on the Block devices window relate to the specific EIDE chipset you use, either on your motherboard or on an add-on card. To get the best performance, you should activate appropriate options.

Kernel Options for SCSI Drives

SCSI options reside in one or two setup windows available from the Linux Kernel Configuration window. In the 2.2.x-series kernels, these options are spread across the SCSI support and SCSI low-level drivers items; in 2.3.x and 2.4.x kernels, the SCSI low-level drivers item has been moved into the SCSI support window as a sub-option. The options required for removable drives are:

• SCSI support You must activate SCSI support. A Y response is required if you boot from a SCSI hard disk, but M is adequate if you boot from an EIDE disk.

• SCSI disk support Like SCSI support, SCSI disk support is required, and must be Y only if you boot from a SCSI hard disk.

• SCSI low-level drivers You must locate and activate the driver for the SCSI host adapter used by the removable disk drive. (See Chapter 9, "SCSI Host Adapters," for more information on SCSI host adapters.) If you boot from a SCSI hard disk, this option must be set to Y; otherwise it can be Y or M.

Chapter 6

Kernel Options for Parallel Port Drives 6

Parallel-interfaced devices use a wide variety of drivers, many of which are tied to specific r products. Options which you might need include O

• General setup, Parallel port support This option is required for all parallel port L removable disks, as well as all other devices that attach to parallel ports. Although you D should be able to answer either Y or M to this option, I recommend Y, because so much S depends on it and I've encountered cases where the kernel module auto-loader has problems with the parallel-port drivers.

• General setup, PC-style hardware If you use an x86 PC, respond Y or M to this option. If you use some other architecture, you might need to select another option, such as Support foreign hardware.

• General setup, Use FIFO/DMA if available Although not strictly required, answering Y to this option has the potential to improve performance, or at least reduce the CPU overhead when you access a parallel-interfaced disk drive.

• Block devices, Parallel port IDE device support This option is required (Y or M) for many such devices, but not for all them.

• Block devices, Parallel port IDE disks This option is used to support parallel-interfaced devices that use IDE without using the ATAPI protocols. If you're uncertain about it, build this support, at least as a module.

• Block devices, Parallel port ATAPI disks This option is like the previous one, but incorporates ATAPI protocols for devices that use them. Again, if you're uncertain, include this support.

• Specific block devices Below the last couple of options are a number of drivers for specific devices, such as the MicroSolutions backpack protocol. You must select at least one of these devices to use an IDE-style parallel port drive. If you don't see your device listed, try doing a search on for help, or simply select all the devices. The file /usr/src/linux/Documentation/paride.txt can also be helpful in determining what driver to select.

• SCSI low-level drivers, IOMEGA parallel port (ppa - older drives) Activate this option if you have an older parallel-port-interfaced Iomega Zip drive. You do not need the parallel-port IDE drivers for this device.

• SCSI low-level drivers, IOMEGA parallel port (imm - newer drives) Use this driver if you have a newer Zip Plus drive with a cable labeled "Auto Detect." You don't need parallel-port IDE drivers for this device.

If you have a SCSI hard disk and a parallel-port Iomega Zip drive, I recommend building the Iomega parallel-port drivers as a module and the driver for your main SCSI host adapter into the kernel. This guarantees that the kernel won't become confused and try to boot from the Zip drive instead of the SCSI boot disk.

When you use a parallel-interfaced device, how you access the drive depends on the sub-variety of interface used, SCSI or IDE. An Iomega Zip drive turns up as an ordinary SCSI device, whereas the IDE drives use special device files. The file

/usr/src/linux/Documentation/paride.txt contains a script you can run to create appropriate device files, if they don't already exist on your system. (Most distributions include these device files.)

Kernel Options for USB Drives

USB kernel options are changing rapidly with the 2.3.x Linux kernels, and will probably vary somewhat from what I describe here for the 2.4.x kernels. If you want to use USB devices with a 2.2.x kernel, you must use a very recent 2.2.x kernel or apply a set of patches to add USB support to the older kernel. Options relevant to USB removable disks include

• USB drivers, Support for USB This option is required to use any USB devices.

• USB chipsets Two USB low-level drivers exist, UHCI and OHCI. You must select whichever one is appropriate for your computer.

• USB drivers, USB SCSI (mass storage) This option includes support for some USB disk devices, treating them as if they were SCSI disks.

• SCSI options The Linux USB support for disk devices relies upon SCSI drivers, so you must activate SCSI drivers as if you were using a SCSI host adapter. You don't need to use drivers in the SCSI menu for any particular SCSI host adapter, however.

Linux kernel support for USB storage devices is weak in the 2.2.x and 2.3.x kernels, but is rapidly improving. With any luck, the support will be reliable early in the 2.4.x series kernels. For the latest information, check

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