This month, I’m going to talk about writing a driver for a simple SCSI controller under Linux. The Linux kernel SCSI layer does most of the work for SCSI device handling, so a simple SCSI driver is relatively painless to write. For more advanced devices, however, the kernel’s SCSI code is actually too clever — there are plans afoot to streamline it and solve these problems.
This month, I’m going to talk about writing a driver for a simple SCSI controller under Linux. The Linux kernel SCSI layer does most of the work for SCSI device handling, so a simple SCSI driver is relatively painless to write. For more advanced devices, however, the kernel’s SCSI code is actually too clever — there are plans afoot to streamline it and solve these problems.
The job of a SCSI driver is different than that of a block device driver. The upper layers of the SCSI code handle CD-ROMs, disks and other devices. Requests from these upper layers are turned into SCSI command blocks before they are fed to your driver. This means your SCSI driver need only worry about low-level SCSI requests and not about other aspects of the kernel device structure.
In order to illustrate SCSI drivers I’m going to invent a SCSI controller that has a simple command interface. Sadly, this is rarely the case for real devices. However, our imaginary SCSI controller will make the examples much easier to follow. This should be enough to get you started — dealing with the complexities of a particular piece of hardware would take up more space than this column allows.
Overall Driver Structure
A Linux SCSI driver contains seven main functions:
* The detect function is called by the SCSI layer when the driver is initialized. It is responsible for scanning…
Please log in to view this content.
Not Yet a Member?
Register with LinuxMagazine.com and get free access to the entire archive, including:
