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readlinkat - read value of a symbolic link relative to a directory file descriptor
#include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> int readlinkat(int dirfd, const char *pathname, char *buf, size_t bufsiz); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): readlinkat(): Since glibc 2.10: _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L Before glibc 2.10: _ATFILE_SOURCE
The readlinkat() system call operates in exactly the same way as readlink(2), except for the differences described in this manual page. If the pathname given in pathname is relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd (rather than relative to the current working directory of the calling process, as is done by readlink(2) for a relative pathname). If pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted relative to the current working directory of the calling process (like readlink(2)). If pathname is absolute, then dirfd is ignored. Since Linux 2.6.39, pathname can be an empty string, in which case the call operates on the file referred to by dirfd (which may have been obtained using the open(2) O_PATH flag). In this case, dirfd can refer to any type of file, not just a directory.
On success, readlinkat() returns the number of bytes placed in buf. On error, -1 is returned and errno is set to indicate the error.
The same errors that occur for readlink(2) can also occur for readlinkat(). The following additional errors can occur for readlinkat(): EBADF dirfd is not a valid file descriptor. ENOTDIR pathname is relative and dirfd is a file descriptor referring to a file other than a directory.
readlinkat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.
See openat(2) for an explanation of the need for readlinkat().
openat(2), readlink(2), path_resolution(7)
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