| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ============================ |
| SCSI subsystem documentation |
| ============================ |
| |
| The Linux Documentation Project (LDP) maintains a document describing |
| the SCSI subsystem in the Linux kernel (lk) 2.4 series. See: |
| https://www.tldp.org/HOWTO/SCSI-2.4-HOWTO . The LDP has single |
| and multiple page HTML renderings as well as postscript and pdf. |
| |
| Notes on using modules in the SCSI subsystem |
| ============================================ |
| The SCSI support in the Linux kernel can be modularized in a number of |
| different ways depending upon the needs of the end user. To understand |
| your options, we should first define a few terms. |
| |
| The scsi-core (also known as the "mid level") contains the core of SCSI |
| support. Without it you can do nothing with any of the other SCSI drivers. |
| The SCSI core support can be a module (scsi_mod.o), or it can be built into |
| the kernel. If the core is a module, it must be the first SCSI module |
| loaded, and if you unload the modules, it will have to be the last one |
| unloaded. In practice the modprobe and rmmod commands |
| will enforce the correct ordering of loading and unloading modules in |
| the SCSI subsystem. |
| |
| The individual upper and lower level drivers can be loaded in any order |
| once the SCSI core is present in the kernel (either compiled in or loaded |
| as a module). The disk driver (sd_mod.o), CD-ROM driver (sr_mod.o), |
| tape driver [1]_ (st.o) and SCSI generics driver (sg.o) represent the upper |
| level drivers to support the various assorted devices which can be |
| controlled. You can for example load the tape driver to use the tape drive, |
| and then unload it once you have no further need for the driver (and release |
| the associated memory). |
| |
| The lower level drivers are the ones that support the individual cards that |
| are supported for the hardware platform that you are running under. Those |
| individual cards are often called Host Bus Adapters (HBAs). For example the |
| aic7xxx.o driver is used to control all recent SCSI controller cards from |
| Adaptec. Almost all lower level drivers can be built either as modules or |
| built into the kernel. |
| |
| .. [1] There is a variant of the st driver for controlling OnStream tape |
| devices. Its module name is osst.o . |
