Define ‘symlinkat’ wrapper when supported.

* configure.ac: Detect whether ‘symlinkat’ exists.
* libguile/filesys.c (scm_symlinkat): Define a Scheme binding
  when it exists.
* libguile/filesys.h: Make the binding part of the public C API.
* doc/ref/posix.texi (File System): Document the binding.
* test-suite/tests/filesys.test ("symlinkat"): Test it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

configure.ac

@@ -517,7 +517,7 @@ AC_CHECK_HEADERS([crt_externs.h])
 #
 AC_CHECK_FUNCS([DINFINITY DQNAN cexp chsize clog clog10 ctermid         \
   fesetround ftime ftruncate fchown fchmod fchdir readlinkat		\
-  getcwd geteuid getsid							\
+  symlinkat getcwd geteuid getsid							\
   gettimeofday getuid getgid gmtime_r ioctl lstat mkdir mkdtemp mknod   \
   nice readlink rmdir setegid seteuid                            \
   setuid setgid setpgid setsid sigaction siginterrupt stat64  \

doc/ref/posix.texi

@@ -909,6 +909,12 @@ Create a symbolic link named @var{newpath} with the value (i.e., pointing to)
 @var{oldpath}.  The return value is unspecified.
 @end deffn
 
+@deffn {Scheme Procedure} symlinkat dir oldpath newpath
+@deffnx {C Function} scm_symlinkat (dir, oldpath, newpath)
+Like @code{symlink}, but resolve @var{newpath} relative to
+the directory referred to by the file port @var{dir}.
+@end deffn
+
 @deffn {Scheme Procedure} mkdir path [mode]
 @deffnx {C Function} scm_mkdir (path, mode)
 Create a new directory named by @var{path}.  If @var{mode} is omitted

libguile/filesys.c

@@ -1032,6 +1032,29 @@ SCM_DEFINE (scm_symlink, "symlink", 2, 0, 0,
 #undef FUNC_NAME
 #endif /* HAVE_SYMLINK */
 
+#ifdef HAVE_SYMLINKAT
+SCM_DEFINE (scm_symlinkat, "symlinkat", 3, 0, 0,
+            (SCM dir, SCM oldpath, SCM newpath),
+            "Like @code{symlink}, but resolve @var{newpath} relative\n"
+            "to the directory referred to by the file port @var{dir}.")
+#define FUNC_NAME s_scm_symlinkat
+{
+  int val;
+  int fdes;
+
+  SCM_VALIDATE_OPFPORT (SCM_ARG1, dir);
+  fdes = SCM_FPORT_FDES (dir);
+  STRING2_SYSCALL (oldpath, c_oldpath,
+		   newpath, c_newpath,
+		   val = symlinkat (c_oldpath, fdes, c_newpath));
+  scm_remember_upto_here_1 (dir);
+  if (val != 0)
+    SCM_SYSERROR;
+  return SCM_UNSPECIFIED;
+}
+#undef FUNC_NAME
+#endif /* HAVE_SYMLINKAT */
+
 /* Static helper function for choosing between readlink
    and readlinkat. */
 static int

libguile/filesys.h

@@ -62,6 +62,7 @@ SCM_API SCM scm_select (SCM reads, SCM writes, SCM excepts, SCM secs, SCM msecs)
 SCM_API SCM scm_fcntl (SCM object, SCM cmd, SCM value);
 SCM_API SCM scm_fsync (SCM object);
 SCM_API SCM scm_symlink (SCM oldpath, SCM newpath);
+SCM_API SCM scm_symlinkat (SCM dir, SCM oldpath, SCM newpath);
 SCM_API SCM scm_readlink (SCM path);
 SCM_API SCM scm_lstat (SCM str);
 SCM_API SCM scm_copy_file (SCM oldfile, SCM newfile);

test-suite/tests/filesys.test

@@ -367,3 +367,30 @@
 
   (false-if-exception (delete-file (test-symlink)))
   (false-if-exception (delete-file (test-file))))
+
+(with-test-prefix "symlinkat"
+  (pass-if-equal "create" (test-file)
+    (unless (defined? 'symlinkat)
+      (throw 'unsupported))
+    (call-with-port
+     (open "." O_RDONLY)
+     (lambda (port)
+       (symlinkat port (test-file) (test-symlink))
+       (readlink (test-symlink)))))
+  (false-if-exception (delete-file (test-symlink)))
+
+  (pass-if-exception "not a port" exception:wrong-type-arg
+    (unless (defined? 'symlinkat)
+      (throw 'unsupported))
+    (symlinkat "bogus" (test-file) (test-symlink)))
+
+  (pass-if-exception "not a file port" exception:wrong-type-arg
+    (unless (defined? 'symlinkat)
+      (throw 'unsupported))
+    (symlinkat (open-input-string "") (test-file) (test-symlink)))
+
+  (pass-if-exception "closed port" exception:wrong-type-arg
+    (unless (defined? 'symlinkat)
+      (throw 'unsupported))
+    (symlinkat (call-with-port (open "." O_RDONLY) identity)
+               (test-file) (test-symlink))))