readlinkat()
Place the contents of a symbolic link found at a given location into a buffer
Synopsis:
#include <fcntl.h>
int readlinkat( int dirfd,
const char* pathname,
char* buf,
size_t bufsize );
Arguments:
- dirfd
- A file descriptor that indicates the base directory for relative filepaths. The pathname given in pathname
is resolved by appending it to the directory associated with dirfd.
You can set this argument to AT_FDCWD to use the current working directory as the base directory.
Note:The QNX OS implementation of the *at() functions differ from the POSIX standards. You must use a file descriptor obtained from an open() or openat() call with the O_DIRECTORY flag set, rather than the O_SEARCH flag on POSIX. Otherwise, the function fails and sets errno to ENOTDIR.
If pathname specifies an absolute path, dirfd has no effect.
- pathname
- The name of the symbolic link.
- buf
- A pointer to a buffer where the function can store the contents of the symbolic link (i.e., the path linked to).
- bufsize
- The size of the buffer.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The readlinkat() function places the contents of the symbolic link named by pathname into the buffer pointed to by buf, which has a size of bufsize. The pathname argument can contain an absolute or relative path. In the latter case, the dirfd argument is used to resolve the pathname, as explained in this argument's description (above).
The function checks if directory searches are permitted using the current permissions of the directory underlying the file descriptor.
QNX OS has no concept of a path operation (open(), readlink(), etc.) that references a path relative to an already open file descriptor (for a directory), as far as the filesystem resource manager is concerned. Therefore, it's not possible to eliminate the race inherent in looking up a pathname with multiple intervening directories or symbolic links. However, readlinkat() can still be used for maintaining a per-thread current working directory, using file descriptors maintained by the application.
The contents of the returned symbolic link don't include a NULL terminator. Their length must be determined from the stat structure returned by lstat(), or by the return value of the readlinkat() call.
If readlinkat() is successful, up to bufsize bytes from the contents of the symbolic link are placed in buf.
Returns:
The number of bytes placed in the buffer, or -1 if an error occurs (errno is set).
Errors:
- EACCES
- Search permission is denied on a component of the path prefix, or you don't have permission to search the directory underlying dirfd.
- EBADF
- The pathname argument does not specify an absolute path and the dirfd argument is neither AT_FDCWD nor a valid file descriptor open for reading.
- EINVAL
- The file named in path isn't a symbolic link.
- EIO
- An I/O error occurred while reading from the filesystem.
- ELOOP
- During resolution of the path argument, a loop was found in the symbolic links or more than SYMLOOP_MAX symbolic links were encountered.
- ENAMETOOLONG
- The length of the path string exceeds PATH_MAX, or the resolution of a symbolic link within path produced a result longer than PATH_MAX.
- ENOENT
- The named file doesn't exist, or path is an empty string.
- ENOTDIR
- One of the following is true:
- A component of the path prefix names an existing file that is neither a directory nor a symbolic link to one.
- The pathname argument contains at least one non-slash character, ends with at least one slash character (/), and the last component names an existing file that is neither a directory nor a symbolic link to one.
- The pathname argument is not absolute and fd is associated with a non-directory file.
- The file descriptor in dirfd was created without O_DIRECTORY set.
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |