Overview

Installable file system entry points are called by the kernel as a result 
of action taken through the published standard file I/O application 
programming interface in OS/2 Version 2.0. 

Installable file systems are installed as OS/2 dynamic link library 
modules . Unlike device drivers, they may include any number of segments, 
all of which will remain after initialization, unless the FSD itself takes 
some action to free them. 

An FSD exports FS entries to the OS/2 kernel using standard PUBLIC 
declarations. Each FS entry is called directly. The OS/2 kernel manages 
the association between internal data structures and FSDs. 

When a file system service is required, OS/2 assembles an argument list, 
and calls the appropriate FS entry for the relevant FSD. If a back-level 
FSD is loaded, the OS/2 kernel assures that all arguments passed and all 
structures passed are understood by the FSD. 

Application program interfaces that are unsupported by an FSD receive an 
UNSUPPORTED FUNCTION error from the FSD. 

Certain routines, for example, FS_PROCESSNAME, may provide no processing, 
no processing is needed, or processing does not make sense. These routines 
return no error, not ERROR_NOT_SUPPORTED.