Reading a Directory

DIR *opendir(char *name);	Opens a directory and returns a handle that allows you to read the directory. Returns NULL if an error occurs.
struct dirent *readdir(DIR *d);	Reads one entry from a directory. A struct dirent contains the field d_name.

readdir.c

Reading an Inode

int stat(char *pathname, struct stat *buffer)

Reads information about a file from an inode and places it into a struct stat. Returns -1 on failure.

struct stat fields

st_dev>	ID of device contaning file
st_ino	The inode number
st_mode	The file mode (including file type)
st_nlink	The number of hard links to the file
st_uid	The uid of the file owner
st_gid	The gid of the file group
st_rdev	The device ID for a special file
st_blksize	The preferred blocksize for I/O
st_blocks	The number of disk blocks allocated for the file
st_atim	Last access time
st_mtim	Last modified time
st_ctim	Last status change time

Decoding Modes

The file type is encoded in the leftmost 4 bits of the sixteen bit mode. The header file defines the following bitmasks:

S_IFMT	mask for the type field
S_IFSOCK	unix domain socket
S_IFLNK	symbolic link
S_IFREG	regular file
S_IFBLK	block device
S_IFDIR	directory
S_IFCHR	character device
S_IFIFO	FIFO

For example, if sb is a struct stat, we can do something based on the file type like this:

switch (sb.st_mode & S_IFMT) {
case S_IFREG: ... ; break;
case S_IFSOCK: ... ; break;
case S_IFDIR: ... ; break;
case S_IFSOCK: ... ; break;
...
}

To test for a single type, there is another collection of macros. For example, we could use S_ISDIR(sb.st_mode) to test for a directory.

S_ISSOCK	unix domain socket
S_ISLNK	symbolic link
S_ISREG	regular file
S_ISBLK	block device
S_ISDIR	directory
S_ISCHR	character device
S_ISFIFO	FIFO

Protection Bit Masks

S_ISUID	setuid bit
S_ISGID	setgid bit
S_ISVTX	sticky bit
S_IRWXU	Owner RWX
S_IRUSR	Owner R
S_IWUSR	Owner W
S_IXUSR	Owner X
S_IRWXG	Group RWX
S_IRGRP	Group R
S_IWGRP	Group W
S_IXGRP	Group X
S_IRWXO	Others RWX
S_IROTH	Others R
S_IWOTH	Others W
S_IXOTH	Others X

For example, to test whether owner write permission is on, we could do

if (sb.st_mode & S_IWUSR) { ... }

User Information

struct passwd *getpwnam(char *name);
struct passwd *getpwuid(uid_t uid);

struct passwd fields

pw_name	username
pw_passwd	password
pw_uid	user ID
pw_gid	group ID
pw_gecos	user information
pw_dir	home directory
pw_shell	shell program

struct timespec Fields

time_t tv_sec	time in seconds
time_t tv_nsec	remainder time in nanoseconds

The function c_time can be applied to a time_t to give a string that is a human readable representation of the time.

fileinfo.c