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File System API

File System API. Operating System Hebrew University Spring 2004. RTFM. Man pages Advanced Programming in the Unix Environment by Stevens. open. #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int open(const char *pathname, int oflag, mode_t mode);.

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File System API

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  1. File System API Operating System Hebrew University Spring 2004

  2. RTFM • Man pages • Advanced Programming in the Unix Environment by Stevens

  3. open #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int open(const char *pathname, int oflag, mode_t mode);

  4. open - errno #include <errno.h> extern int errno; EEXIST, EISDIR, EACCES, ENAMETOOLONG, ENOENT, ENOTDIR, ENXIO, ENODEV, EROFS, ETXTBSY, EFAULT, ELOOP, ENOSPC, ENOMEM, EMFILE, ENFILE

  5. oflag O_RDONLY O_WRONLY O_RDWR O_APPEND O_TRUNC O_NONBLOCK O_SYNC

  6. creat #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int creat(const char *pathname, mode_t mode) == open(pathname, O_WRONLY | O_CREAT | O_TRUNC, mode)

  7. close #include <unistd.h> int close(int filedes)

  8. lseek #include <sys/types.h> #include <unistd.h> off_t lseek(int filedes, off_t offset, int whence)

  9. lseek -- whence SEEK_SET SEEK_CUR SEEK_END ----- Currpos = lseek(fd, 0, SEEK_CUR) Currpos = -1, errno = EPIPE, cannot seek fd

  10. Lseek –file size • Extends file size in kernel • Zero fills

  11. read #include <unistd.h> ssize_t read(int filedes, void *buff, size_t nbytes) Ssize_t = signed integer, size_t = unsigned int Ssize = 0 && errno = EAGAIN = non-block

  12. write #include <unistd.h> ssize_t write(int filedes, const void *buff, size_t nbytes)

  13. Sharing files • Kernel structures • Dup #include <unistd.h> int dup(int filedes);

  14. fcntl #include <sys/types.h> #include <unistd.h> #include <fcntl.h> int fcntl(int filedes, int cmd) F_DUPFD, F_GETFL (O_RDONLY,…)

  15. links • Soft and hard #include <unistd.h> int link(const char *existingpath, const char *newpath) int symlink(const char *actualpath, const char *newpath); int unlink(const char *pathname); int remove(const char *pathname); int rename (const char *oldname, const char *newname);

  16. stat, fstat, lstat #include <sys/types.h> #include <sys/stat.h> int stat(const char *pathname, struct stat *buf) int fstat(int filedes, struct stat *buf) int lstat(const char *pathname, struct stat *buf)

  17. struct stat Struct stat { mode_t st_mode; /* file type and mode (permissions) */ ino_t st_ino; /* serial number */ dev_t st_dev; /* device number (file system) */ dev_t st_rdev; /* device number for special files */ nlink_t st_nlink; /* number of links */ uid_t st_uid; /* user ID of owner */ gid_t st_gid; /* group ID of owner */ off_t st_size; /* size in bytes for regular files */ time_t st_atime; /* last access */ time_t st_mtime; /* last modified */ time_t st_ctime; /* last file status change */ long st_blksize; /* best I/O block size */ long st_blocks; /* number of 512-byte blocks allocated */ }

  18. st_mode ST_ISREG(m) ST_ISDIR(m) ST_ISCHR(m) ST_ISBLK(m) ST_ISFIFO(m) ST_ISLNK(m) – symbolic ST_ISSOCK(m)

  19. File permissions • srwxsrwxtrwx • setuid, setgid, sticky • To access • must have x in all directories in path • r and x in directories are different • Must have wx in dir to create files • To delete, must have wx in dir, file is irrelevent

  20. umask #include <sys/types.h> #include <sys/stat.h> Mode_t umask(mode_t cmask) S_IRUSR, S_IWUSR, S_IXUSR (grp, oth)

  21. chmod #include <sys/types.h> #include <sys/stat.h> int chmod(const char *pathname, mode_t mode) • must be owner to change mode

  22. chown #include <sys/types.h> #include <unistd.h> int chown(const char *pathname, uid_t owner, gid_t group); lchown – does not follow link

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