= Implementation and design of the file system layer =

Unlike in monolitic designs, the file system functionality is spread across
several layers in HelenOS:

 * [#FSDesignLibc standard library support],
 * [#FSDesignVFS VFS server],
 * [#FSDesignFS set of individual file system servers], and
 * [#FSDesignLibFS libfs library].

== Standard library support == #FSDesignLibc

The standard library translates more or less POSIX file system requests made by 
the user application to the VFS server frontend protocol and passes them to
''VFS''. The library emulates some calls such as ''opendir()'', ''readdir()'', 
''rewinddir()'' and ''closedir()'' using other calls. In this case these will
be ''open()'', ''read()'', ''lseek()'' and ''close()''.

The VFS server accepts only absolute file paths and so the standard library 
takes care of providing the ''getcwd()'' and ''chdir()'' interfaces. It also
translates all relative paths to absolute. Passing absolute paths may not be
always optimal, but it simplifies the design of the VFS server and the libfs
algorithms. In addition, thanks to this feature, the ''dot-dot'' file path
components can be processed lexically, which leads to further simplifications.

The standard library forwards all other requests, which it is unable to handle 
itslef, to the VFS server and does not contribute to the file system
functionality by any other means. Each file system request forwarded to VFS
is composed of one or more IPC phone calls.