RTEMS 4.6.1 On-Line Library

Mapping of Generic System Calls to Filesystem Specific Functions

RTEMS Filesystem Design Guide

5.3.1: Mapping of Generic System Calls to Filesystem Specific Functions

The list of generic system calls includes the routines open(), read(), write(), close(), etc..

The Files and Directories section of the POSIX Application Programs Interface specifies a set of functions with calling arguments that are used to gain access to the information in a filesystem. To the application program, these functions allow access to information in any mounted filesystem without explicit knowledge of the filesystem type or the filesystem mount configuration. The following are functions that are provided to the application:

access()
chdir()
chmod()
chown()
close()
closedir()
fchmod()
fcntl()
fdatasync()
fpathconf()
fstat()
fsync()
ftruncate()
link()
lseek()
mkdir()
mknod()
mount()
open()
opendir()
pathconf()
read()
readdir()
rewinddir()
rmdir()
rmnod()
scandir()
seekdir()
stat()
telldir()
umask()
unlink()
unmount()
utime()
write()

The filesystem's type as well as the node type within the filesystem determine the nature of the processing that must be performed for each of the functions above. The RTEMS filesystem provides a framework that allows new filesystem to be developed and integrated without alteration to the basic framework.

To provide the functional switching that is required, each of the POSIX file and directory functions have been implemented as a shell function. The shell function adheres to the POSIX interface standard. Within this functional shell, filesystem and node type information is accessed which is then used to invoke the appropriate filesystem and node type specific routine to process the POSIX function call.

RTEMS Filesystem Design Guide