Operating System Hebrew University Spring 2004 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);

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

oflag O_RDONLY O_WRONLY O_RDWR O_APPEND O_TRUNC O_NONBLOCK O_SYNC

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)

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

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

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

Lseek –file size Extends file size in kernel Zero fills

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

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

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

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

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);

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)

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 */ }

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

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

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

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

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