Driver and module initialization
The Linux SCSI Generic (sg) HOWTO
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Chapter 10. Driver and module initialization

The size of the default reserved buffer can be specified when the sg driver is loaded. If it is built into the kernel then use: 
    sg_def_reserved_size=<n>
on the boot line (only supported in 2.4 kernels).

If sg is a module, it can be loaded with modprobe in either manner: 
    modprobe sg
    modprobe sg def_reserved_size=<n>
In the second case "<n>" is an integer (non negative). The default value is the value of the SG_DEF_RESERVED_SIZE defined in sg.h . This is currently 32768.

If sg is a module, it can be unloaded with rmmod like this: 
    rmmod sg
However if there is a file descriptor still open with the sg driver (or there is an outstanding request awaiting a response) then the sg module is considered to be busy and can't be unloaded.

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Mmap-ed IO Sg and the "proc" file system