Linux System Programming note 8 ——File and Directory Management

1. The Stat Family

#include <sys/types.h>

#include <sys/stat.h>

#include <unistd.h>

int stat(const char *path, struct stat *buf);

int fstat(int fd, struct stat *buf);

int lstat(const char *path, struct stat *buf);

struct stat{

     dev_t st_dev;

     ino_t  st_ino;

     mode_t st_mode;

     nlink_t st_nlink;

     uid_t st_uid;

     gid_t st_gid;

     dev_t st_rdev;

     off_t st_size;

     blksize_t st_blksize;

     blkcnt_t st_blocks;

     time_t st_atime;

     time_t st_mtime;

     time_t st_ctime;

};

2. Permissions

#include <sys/types.h>

#include <sys/stat.h>

int chmod(const char *path, mode_t mode);

int fchmod(int fd, mode_t mode);

3. Ownership

#include <sys/types.h>

#include <unistd.h>

int chown(const char *path, uid_t owner, gid_t group);

int lchown(const char *path, uid_t owner, gid_t group);

int fchown(int fd, uid_t owner, gid_t group);

4. Extended attribute namespaces

system

security

trusted

user

5. Retrieving an extended attribute

#include <sys/types.h>

#inlcude <attr/xattr.h>

ssize_t getxattr(const char *path, const char *key, void *value, size_t size);

ssize_t lgetxattr(const char *path, const char *key, void *value, size_t size);

ssize_t fgetxattr(int fd, const char *key, void *value, size_t size);

6. Setting an extended attribute

#include <sys/types.h>

#include <attr/xattr.h>

int setxattr(const char *path, const char *key, const void *value, size_t size, int flags);

int lsetxattr(const char *path, const char *key, const void *value, size_t size, int flags);

int fsetxattr(int fd, const char *key, const void *value, size_t size, int flags);

7. Listing the extended attributes on a file

#include <sys/types.h>

#include <attr/xattr.h>

ssize_t listxattr(const char *path, char *list, size_t size);

ssize_t llistxattr(const char *path, char *list, size_t size);

ssize_t flistxattr(int fd, char *list, size_t size);

8. Removing an extended attribute

#include <sys/types.h>

#include <attr/xattr.h>

int removexattr(const char *path, const char *key);

int lremovexattr(const char *path, chost char *key);

int fremovexattr(int fd, const char *key);

9. Obtaining the current working directory

#include <unistd.h>

char *getcwd(char *buf, size_t size);

#define _GNU_SOURCE

#include <unistd.h>

char *get_current_dir_name(void);

#define _XOPEN_SOURCE_EXTENDED     /* or _BSD_SOURCE */

#include <unistd.h>

char *getwd(char *buf);

10. Changing the current working directory

#include <unistd.h>

int chdir(const char *path);

int fchdir(int fd);

11. Creating Directories

#include <sys/stat.h>

#include <sys/types.h>

int mkdir(const char *path, mode_t mode);

12. Removing Directories

#include <unistd.h>

int rmdir (const char *path);

13. Reading a Directory's Contents

#include <sys/types.h>

#include <dirent.h>

DIR *opendir(cosnt char *name);

To obtain the file descriptor behind a given directory stream:

#define _BSD_SOURCE /* or _SVID_SOURCE */

#include <sys/types.h>

#include <dirent.h>

int dirfd(DIR *dir);

14. Reading from a directory stream

#include <sys/types.h>

#include <dirent.h>

struct dirent *readdir(DIR *dir);

struct dirent{

     ino_t d_ino;

     off_t d_off;

     unsigned short d_reclen;

     unsigned char d_type;

     char d_name[256];

};

15. Closing the directory stream

#include <sys/types.h>

#include <dirent.h>

int closedir(DIR *dir);

16. System call for reading directory contents

#include <unistd.h>

#include <sys/types.h>

#include <linux/dirent.h>

#include <linux/unistd.h>

#incllude <errno.h>

/*

 * Not defined for user space: need to 

 * use the _syscall3() macro to access

 */

int readdir(unsigned int fd, struct dirent *dirp, unsigned int count);

int getdents(unsigned int fd, struct dirent *dirp, unsigned int count);

You do not want to use these system calls! They are obtuse and not portable.

17. Hard Links

#include <unistd.h>

int link(const char *oldpath, const char *new path);

18. Symbolic Links

#include <unistd.h>

int symlink(const char *oldpath, const char *newpath);

19. Unlinking

#include <unistd.h>

int unlink(const char *pathname);

20. Moving 

#include <stdio.h>

int rename(const char *oldpath, const char *newpath);

21. Monitoring File Events

21.1 Initializing inotify

#include <sys/inotify.h>

int inotify_init1(int flags);

The flags parameter is usually 0, but may be a bitwise OR of the following flags:

IN_CLOEXEC

IN_NONBLOCK

errno:

EMFILE

ENFILE

ENOMEN

example:

int fd;

fd = inotify_init1(0);

if (fd == -1){

     perror("inotify_init1");

     exit(EXIT_FAILURE);

}

21.2 Watches

#include <sys/inotify>

int inotify_add_watch(int fd, const char *path, uint32_t mask);

mask:

IN_ACCESS

IN_MODIFY

IN_ATTRIB

IN_CLOSE_WRITE

IN_CLOSE_NOWRITE

IN_OPEN

IN_MOVED_FROM

IN_MOVED_TO

IN_CREATE

IN_DELETE

IN_DELETE_SELF

IN_MOVE_SELF

The following events are also definedm grouping two or more events into a single value:

IN_ALL_EVENTS

IN_CLOSE

IN_MOVE

21.3 inotify Events

#include <sys/inotify.h>

struct inotify_event{}

     int wd;

     uint32_t mask;

     uint32_t cookie;

     uint32_t len;

     char name[];

};

21.4 Reading inotify events

21.5 Advanced inotify events

IN_IGNORED

IN_ISDIR

IN_Q_OVERFLOW

IN_UNMOUNT

21.6 Removing an inotify Watch

#include <inotify.h>

int inotify_rm_watch(int fd, uint32_t wd);

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