scsi.rst 2.3 KB

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  1. .. SPDX-License-Identifier: GPL-2.0
  2. ============================
  3. SCSI subsystem documentation
  4. ============================
  5. The Linux Documentation Project (LDP) maintains a document describing
  6. the SCSI subsystem in the Linux kernel (lk) 2.4 series. See:
  7. http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO . The LDP has single
  8. and multiple page HTML renderings as well as postscript and pdf.
  9. It can also be found at:
  10. http://web.archive.org/web/%2E/http://www.torque.net/scsi/SCSI-2.4-HOWTO
  11. Notes on using modules in the SCSI subsystem
  12. ============================================
  13. The scsi support in the linux kernel can be modularized in a number of
  14. different ways depending upon the needs of the end user. To understand
  15. your options, we should first define a few terms.
  16. The scsi-core (also known as the "mid level") contains the core of scsi
  17. support. Without it you can do nothing with any of the other scsi drivers.
  18. The scsi core support can be a module (scsi_mod.o), or it can be built into
  19. the kernel. If the core is a module, it must be the first scsi module
  20. loaded, and if you unload the modules, it will have to be the last one
  21. unloaded. In practice the modprobe and rmmod commands (and "autoclean")
  22. will enforce the correct ordering of loading and unloading modules in
  23. the SCSI subsystem.
  24. The individual upper and lower level drivers can be loaded in any order
  25. once the scsi core is present in the kernel (either compiled in or loaded
  26. as a module). The disk driver (sd_mod.o), cdrom driver (sr_mod.o),
  27. tape driver [1]_ (st.o) and scsi generics driver (sg.o) represent the upper
  28. level drivers to support the various assorted devices which can be
  29. controlled. You can for example load the tape driver to use the tape drive,
  30. and then unload it once you have no further need for the driver (and release
  31. the associated memory).
  32. The lower level drivers are the ones that support the individual cards that
  33. are supported for the hardware platform that you are running under. Those
  34. individual cards are often called Host Bus Adapters (HBAs). For example the
  35. aic7xxx.o driver is used to control all recent SCSI controller cards from
  36. Adaptec. Almost all lower level drivers can be built either as modules or
  37. built into the kernel.
  38. .. [1] There is a variant of the st driver for controlling OnStream tape
  39. devices. Its module name is osst.o .