fdatasync: new module

At least libvirt would like to use the lighter-weight fdatasync
on platforms where it is supported, while still guaranteeing full
sync (via the heavy-weight fsync fallback) on all platforms.

I've got an open question to the Austin Group, since the POSIX 2008
wording is self-contradictory (unlike fsync, fdatasync requires
EBADF on non-writable fds, but still mentions that read() errors
must be propagated).  I can see how fsync() would affect atime after
read() while fdatasync() can skip that, explaining why fdatasync()
might have the EBADF requirement, but on the other hand, that prevents
an implementation (like ours) where fdatasync is a straight alias of
fsync.  At any rate, glibc allows fdatasync on read-only fds.

* modules/fsync (Description): Document difference to fdatasync.
* modules/fdatasync: New module.
* m4/fdatasync.m4 (gl_FUNC_FDATASYNC): New file.
* lib/fdatasync.c (fdatasync): Likewise.
* m4/unistd_h.m4 (gl_UNISTD_H, gl_UNISTD_H_DEFAULTS): Set up
defaults.
* modules/unistd (Makefile.am): Set witnesses.
* lib/unistd.in.h (fdatasync): Declare.
* MODULES.html.sh: Document it.
* doc/posix-functions/fdatasync.texi (fdatasync): Likewise.
* modules/fdatasync-tests: New test.
* tests/test-fdatasync.c: Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>

ChangeLog

@@ -1,3 +1,19 @@
+2011-09-16  Eric Blake  <eblake@redhat.com>
+
+	fdatasync: new module
+	* modules/fsync (Description): Document difference to fdatasync.
+	* modules/fdatasync: New module.
+	* m4/fdatasync.m4 (gl_FUNC_FDATASYNC): New file.
+	* lib/fdatasync.c (fdatasync): Likewise.
+	* m4/unistd_h.m4 (gl_UNISTD_H, gl_UNISTD_H_DEFAULTS): Set up
+	defaults.
+	* modules/unistd (Makefile.am): Set witnesses.
+	* lib/unistd.in.h (fdatasync): Declare.
+	* MODULES.html.sh: Document it.
+	* doc/posix-functions/fdatasync.texi (fdatasync): Likewise.
+	* modules/fdatasync-tests: New test.
+	* tests/test-fdatasync.c: Likewise.
+
 2011-09-16  Eric Blake  <eblake@redhat.com>
 
 	test-fsync: enhance tests

MODULES.html.sh

@@ -2356,6 +2356,7 @@ func_all_modules ()
   func_module fclose
   func_module fcntl-h
   func_module fcntl
+  func_module fdatasync
   func_module flock
   func_module fopen
   func_module fprintf-posix

doc/posix-functions/fdatasync.texi

@@ -4,15 +4,15 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/fdatasync.html}
 
-Gnulib module: ---
+Gnulib module: fdatasync
 
 Portability problems fixed by Gnulib:
 @itemize
-@end itemize
-
-Portability problems not fixed by Gnulib:
-@itemize
 @item
 This function is missing on some platforms:
 MacOS X 10.5, FreeBSD 6.0, OpenBSD 3.8, Minix 3.1.8, IRIX 5.3, Solaris 2.4, mingw, MSVC 9, Interix 3.5, BeOS.
 @end itemize
+
+Portability problems not fixed by Gnulib:
+@itemize
+@end itemize

lib/fdatasync.c

@@ -0,0 +1,25 @@
+/* Emulate fdatasync on platforms that lack it.
+
+   Copyright (C) 2011 Free Software Foundation, Inc.
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+#include <unistd.h>
+
+int
+fdatasync (int fd)
+{
+  return fsync (fd);
+}

lib/unistd.in.h

@@ -484,8 +484,27 @@ _GL_WARN_ON_USE (fchownat, "fchownat is not portable - "
 #endif
 
 
-#if @GNULIB_FSYNC@
+#if @GNULIB_FDATASYNC@
 /* Synchronize changes to a file.
+   Return 0 if successful, otherwise -1 and errno set.
+   See POSIX:2001 specification
+   <http://www.opengroup.org/susv3xsh/fdatasync.html>.  */
+# if !@HAVE_FDATASYNC@
+_GL_FUNCDECL_SYS (fdatasync, int, (int fd));
+# endif
+_GL_CXXALIAS_SYS (fdatasync, int, (int fd));
+_GL_CXXALIASWARN (fdatasync);
+#elif defined GNULIB_POSIXCHECK
+# undef fdatasync
+# if HAVE_RAW_DECL_FDATASYNC
+_GL_WARN_ON_USE (fdatasync, "fdatasync is unportable - "
+                 "use gnulib module fdatasync for portability");
+# endif
+#endif
+
+
+#if @GNULIB_FSYNC@
+/* Synchronize changes, including metadata, to a file.
    Return 0 if successful, otherwise -1 and errno set.
    See POSIX:2001 specification
    <http://www.opengroup.org/susv3xsh/fsync.html>.  */

m4/fdatasync.m4

@@ -0,0 +1,14 @@
+# fdatasync.m4 serial 1
+dnl Copyright (C) 2008-2011 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_FDATASYNC],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_CHECK_FUNCS_ONCE([fdatasync])
+  if test $ac_cv_func_fdatasync = no; then
+    HAVE_FDATASYNC=0
+  fi
+])

m4/unistd_h.m4

@@ -1,4 +1,4 @@
-# unistd_h.m4 serial 58
+# unistd_h.m4 serial 59
 dnl Copyright (C) 2006-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -40,7 +40,7 @@ AC_DEFUN([gl_UNISTD_H],
 # endif
 #endif
     ]], [chown dup2 dup3 environ euidaccess faccessat fchdir fchownat
-    fsync ftruncate getcwd getdomainname getdtablesize getgroups
+    fdatasync fsync ftruncate getcwd getdomainname getdtablesize getgroups
     gethostname getlogin getlogin_r getpagesize getusershell setusershell
     endusershell group_member lchown link linkat lseek pipe pipe2 pread pwrite
     readlink readlinkat rmdir sleep symlink symlinkat ttyname_r unlink unlinkat
@@ -67,6 +67,7 @@ AC_DEFUN([gl_UNISTD_H_DEFAULTS],
   GNULIB_FACCESSAT=0;            AC_SUBST([GNULIB_FACCESSAT])
   GNULIB_FCHDIR=0;               AC_SUBST([GNULIB_FCHDIR])
   GNULIB_FCHOWNAT=0;             AC_SUBST([GNULIB_FCHOWNAT])
+  GNULIB_FDATASYNC=0;            AC_SUBST([GNULIB_FDATASYNC])
   GNULIB_FSYNC=0;                AC_SUBST([GNULIB_FSYNC])
   GNULIB_FTRUNCATE=0;            AC_SUBST([GNULIB_FTRUNCATE])
   GNULIB_GETCWD=0;               AC_SUBST([GNULIB_GETCWD])
@@ -110,6 +111,7 @@ AC_DEFUN([gl_UNISTD_H_DEFAULTS],
   HAVE_FACCESSAT=1;       AC_SUBST([HAVE_FACCESSAT])
   HAVE_FCHDIR=1;          AC_SUBST([HAVE_FCHDIR])
   HAVE_FCHOWNAT=1;        AC_SUBST([HAVE_FCHOWNAT])
+  HAVE_FDATASYNC=1;       AC_SUBST([HAVE_FDATASYNC])
   HAVE_FSYNC=1;           AC_SUBST([HAVE_FSYNC])
   HAVE_FTRUNCATE=1;       AC_SUBST([HAVE_FTRUNCATE])
   HAVE_GETDTABLESIZE=1;   AC_SUBST([HAVE_GETDTABLESIZE])

modules/fdatasync

@@ -0,0 +1,28 @@
+Description:
+fdatasync(2) function: synchronize writes to a file.
+
+Files:
+lib/fdatasync.c
+m4/fdatasync.m4
+
+Depends-on:
+fsync
+unistd
+
+configure.ac:
+gl_FUNC_FDATASYNC
+if test $HAVE_FDATASYNC = 0; then
+  AC_LIBOBJ([fdatasync])
+fi
+gl_UNISTD_MODULE_INDICATOR([fdatasync])
+
+Makefile.am:
+
+Include:
+<unistd.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Eric Blake

modules/fdatasync-tests

@@ -0,0 +1,13 @@
+Files:
+tests/test-fdatasync.c
+tests/signature.h
+tests/macros.h
+
+Depends-on:
+errno
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-fdatasync
+check_PROGRAMS += test-fdatasync

modules/fsync

@@ -1,5 +1,5 @@
 Description:
-fsync(2) function: synchronize writes to a file.
+fsync(2) function: synchronize writes, including metadata, to a file.
 
 Files:
 lib/fsync.c

modules/unistd

@@ -39,6 +39,7 @@ unistd.h: unistd.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H
 	      -e 's/@''GNULIB_FACCESSAT''@/$(GNULIB_FACCESSAT)/g' \
 	      -e 's/@''GNULIB_FCHDIR''@/$(GNULIB_FCHDIR)/g' \
 	      -e 's/@''GNULIB_FCHOWNAT''@/$(GNULIB_FCHOWNAT)/g' \
+	      -e 's/@''GNULIB_FDATASYNC''@/$(GNULIB_FDATASYNC)/g' \
 	      -e 's/@''GNULIB_FSYNC''@/$(GNULIB_FSYNC)/g' \
 	      -e 's/@''GNULIB_FTRUNCATE''@/$(GNULIB_FTRUNCATE)/g' \
 	      -e 's/@''GNULIB_GETCWD''@/$(GNULIB_GETCWD)/g' \
@@ -82,6 +83,7 @@ unistd.h: unistd.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H
 	      -e 's|@''HAVE_FACCESSAT''@|$(HAVE_FACCESSAT)|g' \
 	      -e 's|@''HAVE_FCHDIR''@|$(HAVE_FCHDIR)|g' \
 	      -e 's|@''HAVE_FCHOWNAT''@|$(HAVE_FCHOWNAT)|g' \
+	      -e 's|@''HAVE_FDATASYNC''@|$(HAVE_FDATASYNC)|g' \
 	      -e 's|@''HAVE_FSYNC''@|$(HAVE_FSYNC)|g' \
 	      -e 's|@''HAVE_FTRUNCATE''@|$(HAVE_FTRUNCATE)|g' \
 	      -e 's|@''HAVE_GETDTABLESIZE''@|$(HAVE_GETDTABLESIZE)|g' \

tests/test-fdatasync.c

@@ -0,0 +1,64 @@
+/* Test of fdatasync() function.
+   Copyright (C) 2008-2011 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (fdatasync, int, (int));
+
+#include <errno.h>
+#include <fcntl.h>
+
+#include "macros.h"
+
+int
+main (void)
+{
+  int fd;
+  const char *file = "test-fdatasync.txt";
+
+  if (fdatasync (STDOUT_FILENO) != 0)
+    {
+      ASSERT (errno == EINVAL /* POSIX */
+              || errno == ENOTSUP /* seen on MacOS X 10.5 */
+              || errno == EBADF /* seen on AIX 7.1 */
+              );
+    }
+  errno = 0;
+  ASSERT (fdatasync (-1) == -1);
+  ASSERT (errno == EBADF);
+  fd = open (file, O_WRONLY|O_CREAT|O_TRUNC, 0644);
+  ASSERT (0 <= fd);
+  ASSERT (write (fd, "hello", 5) == 5);
+  ASSERT (fdatasync (fd) == 0);
+  ASSERT (close (fd) == 0);
+#if 0
+  /* POSIX is self-contradictory on whether fdatasync must fail on
+     read-only file descriptors.  Glibc allows it, as does our
+     implementation if fsync allows it.  */
+  fd = open (file, O_RDONLY);
+  ASSERT (0 <= fd);
+  errno = 0;
+  ASSERT (fdatasync (fd) == -1);
+  ASSERT (errno == EBADF);
+  ASSERT (close (fd) == 0);
+#endif
+  ASSERT (unlink (file) == 0);
+
+  return 0;
+}