Implementation status: to be implemented

Synopsis

#include <sys/stat.h>int futimens(int fd, const struct timespec times[2]);`

#include <fcntl.h>
int utimensat(int fd, const char *path, const struct timespec times[2], int flag);

#include <sys/time.h>
int utimes(const char *path, const struct timeval times[2]);

Description

The functions set file access and modification times for the file argument.

The structures used by functions are defined as follows:

struct timespec {
time_t tv_sec; /* whole seconds (valid values are >=0) */
long tv_nsec; /* nanoseconds (valid values are [0,999999999]) */
};

struct timeval {
time_t tv_sec ; /* whole seconds (valid values are >=0) */
suseconds_t tv_usec; /* microseconds */
};

Arguments:

fd - a file descriptor of the file,
path - a path to the file,
times - an array of two timespec structures. The first array member represents the date and time of last access, and the second member represents the date and time of last modification. The times in the timespec structure are measured in seconds and nanoseconds since the Epoch. The file's relevant timestamp is set to the greatest value supported by the file system that is not greater than the specified time.
flag - 0 or AT_SYMLINK_NOFOLLOW, what means that if path names a symbolic link, then the access and modification times of the symbolic link are changed rather than the file to which it refers.

The futimens() and utimensat() functions set the access and modification times of a file to the values of the times argument. The futimens() function changes the times of the file associated with the file descriptor fd. The utimensat() function changes the times of the file pointed to by the path argument, relative to the directory associated with the file descriptor fd. Both functions allow time specifications accurate to the nanosecond.

For futimens() and utimensat(), the times argument is an array of two timespec structures. The first array member represents the date and time of last access, and the second member represents the date and time of last modification. The times in the timespec structure are measured in seconds and nanoseconds since the Epoch. The file's relevant timestamp is set to the greatest value supported by the file system that is not greater than the specified time.

If the tv_nsec field of a timespec structure has the special value UTIME_NOW, the file's relevant timestamp is set to the greatest value supported by the file system that is not greater than the current time. If the tv_nsec field has the special value UTIME_OMIT, the file's relevant timestamp is not changed. In either case, the tv_sec field is ignored.

If the times argument is a null pointer, both the access and modification timestamps are set to the greatest value supported by the file system that is not greater than the current time. If utimensat() is passed a relative path in the path argument, the file to be used is relative to the directory associated with the file descriptor fd instead of the current working directory. If the access mode of the open file description associated with the file descriptor is not O_SEARCH, the function checks whether directory searches are permitted using the current permissions of the directory underlying the file descriptor. If the access mode is O_SEARCH, the function does not perform the check.

If utimensat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used.

Only a process with the effective user ID equal to the user ID of the file, or with write access to the file, or with appropriate privileges may use futimens() or utimensat() with a null pointer as the times argument or with both tv_nsec fields set to the special value UTIME_NOW. Only a process with the effective user ID equal to the user ID of the file or with appropriate privileges may use futimens() or utimensat() with a non-null times argument that does not have both tv_nsec fields set to UTIME_NOW and does not have both tv_nsec fields set to UTIME_OMIT. If both tv_nsec fields are set to UTIME_OMIT, no ownership or permissions check is performed for the file, but other error conditions may still be detected (including [EACCES] errors related to the path prefix).

Upon successful completion, futimens() and utimensat() mark the last file status change timestamp for update, with the exception that if both tv_nsec fields are set to UTIME_OMIT, the file status change timestamp need not be marked for update.

The utimes() function is equivalent to the utimensat() function with the special value AT_FDCWD as the fd argument and the flag argument set to zero, except that the times argument is a timeval structure rather than a timespec structure, and accuracy is only to the microsecond, not nanosecond, and rounding towards the nearest second may occur.

Return value

Upon successful completion, the functions return 0, otherwise the return -1 and set errno to indicate the error. If -1 is returned, the file times are not affected.

Errors

[EACCES] The times argument is a null pointer, or both tv_nsec values are UTIME_NOW, and the effective user ID of the process does not match the owner of the file and write access is denied.
[EINVAL] Either of the times argument structures specified a tv_nsec value that was neither UTIME_NOW nor UTIME_OMIT, and was a value less than zero or greater than or equal to 1000 million.
[EINVAL] A new file timestamp would be a value whose tv_sec component is not a value supported by the file system.
[EPERM] The times argument is not a null pointer, does not have both tv_nsec fields set to UTIME_NOW, does not have both tv_nsec fields set to UTIME_OMIT, the calling process' effective user ID does not match the owner of the file, and the calling process does not have appropriate privileges.
[EROFS] The file system containing the file is read-only.

The futimens() function fails if:

[EBADF] The fd argument is not a valid file descriptor.

The utimensat() function fails if:

[EACCES] The access mode of the open file description associated with fd is not O_SEARCH and the permissions of the directory underlying fd do not permit directory searches.
[EBADF] The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for reading or searching.
[ENOTDIR] The path argument is not an absolute path and fd is a file descriptor associated with a non-directory file.

The utimensat() and utimes() functions fail if:

[EACCES] Search permission is denied by a component of the path prefix.
[EINVAL] The value of the flag argument is not valid.
[ELOOP] A loop exists in symbolic links or more than {SYMLOOP_MAX} symbolic links are encountered during resolution of the path argument.
[ENAMETOOLONG] The length of a component of a pathname is longer than {NAME_MAX} or
the length of a pathname exceeds {PATH_MAX}, or
pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.
[ENOENT] A component of path does not name an existing file or path is an empty string.
[ENOTDIR]A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory, or the path argument contains at least one non- character and ends with one or more trailing characters and the last pathname component names an existing file that is neither a directory nor a symbolic link to a directory.

Implementation tasks:

  • Implement the futimens() function.
  • Implement the utimensat() function.
  • Implement the utimes() function.