There are many SCSI related modules. The mid and upper level modules are listed below:
scsi_mod.o
sd_mod.o
sr_mod.o
st.o [osst.o]
sg.o
Notice that the first 3 have "_mod" appended to their normal driver names. Lower level drivers tend to use the name (or an abbreviation) of the HBA's manufacturer (e.g. advansys) plus optionally the chip number of the major controller chip (e.g. sym53c8xx for symbios controllers based on the NCR 53c8?? family of chips).
All SCSI modules depend on the mid level. This means if the SCSI mid
level is not built into the kernel and if scsi_mod.o
has not already been loaded then a command like modprobe st
will cause the scsi_mod.o module to be loaded. There
could well be other dependencies, for example modprobe sr_mod
will also cause the cdrom module to be loaded if it hasn't been
already. Also if the SCSI mid level is a module, then all other SCSI
subsystem drivers must be modules (this is enforced by the kernel build
configuration tools).
Modules can be loaded with the modprobe <module_name>
command which will try to load any modules that the
nominated <module_name> depends on.
Also <module_name> does not need the trailing ".o" extension which
is assumed if not given. The insmod <module_name>
command will also try
and load <module_name> but without first loading modules it depends on.
Rules for how modules can cause other modules to be loaded (with
appropriate parameters appended) are usually placed in the file
/etc/modules.conf. [Note that in earlier Linux kernels
this file was often called /etc/conf.modules.]
For further information about the format of this file try
man modules.conf.
Any module can have its allowable command line parameters queried with this command: modinfo -p <module_name>.
When upper level drivers are initialized and if there are no hosts active
then the mid level will attempt to load a module called "scsi_hostadapter".
An "alias" can then be used to associate "scsi_hostadapter" with the actual
name of the lower level (adapter) driver.
For example, a line like "alias scsi_hostadapter aic7xxx" in the
/etc/modules.conf file would cause the aic7xxx module
to be loaded (if there were no lower level drivers already active).
[4]
There is a special relationship between the module parameter "scsi_hostadapter" and the initrd file system. For more information see man initrd and man mkinitrd. [5]
[4]
There is a sequencing issue here if the root file system is on the SCSI
device controlled by the lower level (adapter) driver to be loaded since
it contains the /etc/modules.conf file. Also there
is the issue of how the boot loader obtains the initial kernel image from
a SCSI device (often from the (master) boot record). The latter is usually
taken care of by the system's or adapter card's BIOS.
[5]
An example of using mkinitrd: assume the root
partition is on a SCSI disk connected to a controller from
Adaptec that requires the aic7xxx driver. After
building a kernel with the aic7xxx driver specified as a module then
load the image into the normal place (probably in the
/boot directory). Next make sure a line like
"alias scsi_hostadapter aic7xxx" is in the /etc/modules.conf
file. Then from the /boot directory
execute a line like mkinitrd /boot/initrd-2.4.5.img 2.4.5
(this assumes lk 2.4.5 is being build). This should result in the
file initrd-2.4.5.img being created. The
/etc/lilo.conf should then have a section added
looking something like this:
image=/boot/vmlinuz-2.4.5
label=linux
initrd=/boot/initrd-2.4.5.img
read-only
root=/dev/sda7
The following should also be selected in the kernel configuration:
CONFIG_BLK_DEV_RAM=y CONFIG_BLK_DEV_RAM_SIZE=4096 CONFIG_BLK_DEV_INITRD=y
See also Documentation/initrd.txt.