Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+SCSI subsystem documentation
+============================
+The Linux Documentation Project (LDP) maintains a document describing
+the SCSI subsystem in the Linux kernel (lk) 2.4 series. See:
+http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO . The LDP has single
+and multiple page HTML renderings as well as postscript and pdf.
+It can also be found at:
+http://web.archive.org/web/*/http://www.torque.net/scsi/SCSI-2.4-HOWTO
+
+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 (and "autoclean")
+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), cdrom driver (sr_mod.o),
+tape driver ** (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.
+
+
+** There is a variant of the st driver for controlling OnStream tape
+   devices. Its module name is osst.o .
+