libc: add freadlink(3)

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D56365

include/unistd.h

@@ -518,6 +518,7 @@ int	 execvpe(const char *, char * const *, char * const *);
 int	 feature_present(const char *);
 int	 fchroot(int);
 char	*fflagstostr(u_long);
+ssize_t	 freadlink(int fd, char *buf, size_t bufsize);
 int	 getdomainname(char *, int);
 int	 getentropy(void *, size_t);
 int	 getgrouplist(const char *, gid_t, gid_t *, int *);

lib/libc/gen/Makefile.inc

@@ -56,6 +56,7 @@ SRCS+= \
 	fmtmsg.c \
 	fnmatch.c \
 	fpclassify.c \
+	freadlink.c \
 	frexp.c \
 	fstab.c \
 	ftok.c \

lib/libc/gen/Symbol.map

@@ -475,6 +475,7 @@ FBSD_1.8 {
 };
 
 FBSD_1.9 {
+	freadlink;
 	posix_spawn_file_actions_addchdir;
 	posix_spawn_file_actions_addfchdir;
 	posix_spawnattr_getexecfd_np;

lib/libc/gen/freadlink.c

@@ -0,0 +1,16 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2026 The FreeBSD Foundation
+ *
+ * This software were developed by Konstantin Belousov <kib@FreeBSD.org>
+ * under sponsorship from the FreeBSD Foundation.
+ */
+
+#include <unistd.h>
+
+ssize_t
+freadlink(int fd, char *buf, size_t bufsize)
+{
+	return (readlinkat(fd, "", buf, bufsize));
+}