Development and Implementation of a File System for Gannet Virtual ...

B. File System API
Application Program Interfaces listed below, taken from POSIX standard interface
(Lewine 1991).
1. open() : Opens a file if the file exists or creates a new file does not exist.
Arguments:
int open(const char *path, mode_t oflag);
Path : Pointer to path of the file to open.
oflag : Symbolic flags (Permission bits if a file is created)
Returns:
A file descriptor or -1 on error.
Description:
The open() function establishes a connection between a file and a file descriptor.
The file descriptor is a small integer that is used by I/O functions to reference
the file. The path argument points to the pathname for the file. The oflag
argument is the bitwise inclusive OR of the values of symbolic constants. The
programmer must specify exactly one of the following three symbols:
O_RDONLY : Open for reading only.
O_WRONLY : Open for writing only.
2. creat()—Creates a new file or rewrites an existing one.
Arguments:
int creat(const char *path, mode_t mode);
path : Pointer to path of the file to be created.
mode : Permission bits for the new file.
Returns:
A file descriptor or -1 on error.
Description:
It opens a file for writing. If the file does not exist, it is created with the
permission bits set from mode and the owner and group IDs are set from the
effective user and group ID of the calling process. The file descriptor returned by
creat() may be used only for writing.
3. read() : Reads from a file.
Arguments:
size_t read(int fildes, void *buf, unsigned int nbyte);
fildes :File descriptor open for reading.
buf : Pointer to the place where the data should be read.
63