readlink

Synopsis

#include <unistd.h>

ssize_t readlink(const char *restrict path, char *restrict buf, size_t bufsize);

Status

Implemented

Conformance

IEEE Std 1003.1-2017

Description

The readlink() function shall place the contents of the symbolic link referred to by path in the buffer buf which has size bufsize. If the number of bytes in the symbolic link is less than bufsize, the contents of the remainder of buf are unspecified. If the buf argument is not large enough to contain the link content, the first bufsize bytes shall be placed in buf.

If the value of bufsize is greater than SSIZE_MAX, the result is implementation-defined.

Upon successful completion, readlink() shall mark for update the last data access timestamp of the symbolic link.

Applications should not assume that the contents of the symbolic link placed in buf are null-terminated.

Return value

Upon successful completion, readlink() shall return the count of bytes placed in the buffer. Otherwise, it shall return a value of -1, leave the buffer unchanged, and set errno to indicate the error.

Errors

The readlink() function shall fail if:

• EACCES - Search permission is denied for a component of the path prefix of path.

• EINVAL - The path argument names a file that is not a symbolic link.

• EIO - An I/O error occurred while reading from the file system.

• ELOOP - A loop exists in symbolic links encountered during resolution of the path argument.

• ENAMETOOLONG - The length of a component of a path name is longer than the name length limit of the filesystem, which may differ from NAME_MAX (see POSIX deviations).

• 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-<slash> character and ends with one or more trailing <slash> characters and the last path name component names an existing file that is neither a directory nor a symbolic link to a directory.

The readlink() function may fail if:

• ELOOP - More than SYMLOOP_MAX symbolic links were encountered during resolution of the path argument.

• ENAMETOOLONG - The length of a path name exceeds PATH_MAX, or path name resolution of a symbolic link produced an intermediate result with a length that exceeds PATH_MAX.

POSIX deviations

The length of a path name component is not checked against NAME_MAX by libphoenix, but by the filesystem server, against the name length limit of the filesystem, which may differ from NAME_MAX. readlink() only looks the name up, so the error reported for a too-long component depends on the filesystem: jffs2 reports ENAMETOOLONG, while ext2 and dummyfs check the length only when a new directory entry is created, so the lookup of the name fails with ENOENT. Checking every component in libphoenix would require knowing the name length limit of every mounted filesystem in each process, so the check is left to the filesystem server, which knows its own limit.