Add ‘nofollow’ flag to set-file-times

This is a companion to the recent set-file-modes patch.
It adds support for a ‘nofollow’ flag to set-file-times (Bug#39773).
Like the set-file-modes patch, it needs work in the w32 port.
* admin/merge-gnulib (GNULIB_MODULES): Add futimens, utimensat.
Remove utimens.
* doc/lispref/files.texi (Changing Files):
* etc/NEWS: Mention the change.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* lisp/files.el (copy-directory):
* lisp/gnus/gnus-cloud.el (gnus-cloud-replace-file):
* lisp/net/tramp-adb.el (tramp-adb-handle-copy-file):
* lisp/net/tramp-smb.el (tramp-smb-handle-copy-file):
* lisp/tar-mode.el (tar-copy):
* test/lisp/filenotify-tests.el (file-notify-test03-events):
* test/lisp/files-tests.el:
(files-tests-file-name-non-special-set-file-times):
* test/lisp/net/tramp-tests.el (tramp-test22-file-times):
When setting file times, avoid following symbolic links
when the file is not supposed to be a symbolic link.
* lib/futimens.c, lib/utimensat.c, m4/futimens.m4, m4/utimensat.m4:
New files, copied from Gnulib.
* lisp/gnus/gnus-cloud.el (gnus-cloud-replace-file):
When creating a file that is not supposed to exist already,
use the excl flag to check this.
* lisp/net/tramp-adb.el (tramp-adb-handle-set-file-times):
* lisp/net/tramp-sh.el (tramp-sh-handle-set-file-times):
* lisp/net/tramp-sudoedit.el (tramp-sudoedit-handle-set-file-times):
Accept an optional FLAG arg that is currently ignored,
and add a FIXME comment for it.
* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-set-file-times):
* src/fileio.c (Fset_file_times):
Support an optional FLAG arg.
* src/fileio.c (Fcopy_file): Use futimens instead of set_file_times,
as it’s simpler and is a POSIX API.
* src/sysdep.c (set_file_times): Move from here ...
* src/w32.c (set_file_times): ... to here, and make it static,
since it is now used only in w32.c.  Presumably w32.c should also
add support for futimens and utimensat (the POSIX APIs, which
Emacs now uses) and it can remove fdutimens (the Gnulib API,
which Emacs no longer uses).

3 files changed, 224 insertions, 1 deletions

diff --git a/lib/futimens.c b/lib/futimens.c
new file mode 100644
index 00000000000..83fb27cb6aa
--- /dev/null
+++ b/lib/futimens.c
@@ -0,0 +1,37 @@
+/* Set the access and modification time of an open fd.
+   Copyright (C) 2009-2020 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 <https://www.gnu.org/licenses/>.  */
+
+/* written by Eric Blake */
+
+#include <config.h>
+
+#include <sys/stat.h>
+
+#include "utimens.h"
+
+/* Set the access and modification timestamps of FD to be
+   TIMESPEC[0] and TIMESPEC[1], respectively.
+   Fail with ENOSYS on systems without futimes (or equivalent).
+   If TIMESPEC is null, set the timestamps to the current time.
+   Return 0 on success, -1 (setting errno) on failure.  */
+int
+futimens (int fd, struct timespec const times[2])
+{
+  /* fdutimens also works around bugs in native futimens, when running
+     with glibc compiled against newer headers but on a Linux kernel
+     older than 2.6.32.  */
+  return fdutimens (fd, NULL, times);
+}
diff --git a/lib/gnulib.mk.in b/lib/gnulib.mk.in
index d4dc6a3df33..e90d2e39049 100644
--- a/lib/gnulib.mk.in
+++ b/lib/gnulib.mk.in
@@ -106,6 +106,7 @@
 #  fstatat \
 #  fsusage \
 #  fsync \
+#  futimens \
 #  getloadavg \
 #  getopt-gnu \
 #  gettime \
@@ -155,7 +156,7 @@
 #  timespec-sub \
 #  unlocked-io \
 #  update-copyright \
-#  utimens \
+#  utimensat \
 #  vla \
 #  warnings
 
@@ -1087,6 +1088,7 @@ gl_GNULIB_ENABLED_lchmod = @gl_GNULIB_ENABLED_lchmod@
 gl_GNULIB_ENABLED_malloca = @gl_GNULIB_ENABLED_malloca@
 gl_GNULIB_ENABLED_open = @gl_GNULIB_ENABLED_open@
 gl_GNULIB_ENABLED_strtoll = @gl_GNULIB_ENABLED_strtoll@
+gl_GNULIB_ENABLED_utimens = @gl_GNULIB_ENABLED_utimens@
 gl_LIBOBJS = @gl_LIBOBJS@
 gl_LTLIBOBJS = @gl_LTLIBOBJS@
 gltests_LIBOBJS = @gltests_LIBOBJS@
@@ -1733,6 +1735,17 @@ EXTRA_libgnu_a_SOURCES += fsync.c
 endif
 ## end   gnulib module fsync
 
+## begin gnulib module futimens
+ifeq (,$(OMIT_GNULIB_MODULE_futimens))
+
+
+EXTRA_DIST += futimens.c
+
+EXTRA_libgnu_a_SOURCES += futimens.c
+
+endif
+## end   gnulib module futimens
+
 ## begin gnulib module getdtablesize
 ifeq (,$(OMIT_GNULIB_MODULE_getdtablesize))
 
@@ -3375,13 +3388,26 @@ endif
 ## begin gnulib module utimens
 ifeq (,$(OMIT_GNULIB_MODULE_utimens))
 
+ifneq (,$(gl_GNULIB_ENABLED_utimens))
 libgnu_a_SOURCES += utimens.c
 
+endif
 EXTRA_DIST += utimens.h
 
 endif
 ## end   gnulib module utimens
 
+## begin gnulib module utimensat
+ifeq (,$(OMIT_GNULIB_MODULE_utimensat))
+
+
+EXTRA_DIST += at-func.c utimensat.c
+
+EXTRA_libgnu_a_SOURCES += at-func.c utimensat.c
+
+endif
+## end   gnulib module utimensat
+
 ## begin gnulib module verify
 ifeq (,$(OMIT_GNULIB_MODULE_verify))
 
diff --git a/lib/utimensat.c b/lib/utimensat.c
new file mode 100644
index 00000000000..63788d56480
--- /dev/null
+++ b/lib/utimensat.c
@@ -0,0 +1,160 @@
+/* Set the access and modification time of a file relative to directory fd.
+   Copyright (C) 2009-2020 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 <https://www.gnu.org/licenses/>.  */
+
+/* written by Eric Blake */
+
+#include <config.h>
+
+/* Specification.  */
+#include <sys/stat.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+
+#include "stat-time.h"
+#include "timespec.h"
+#include "utimens.h"
+
+#if HAVE_UTIMENSAT
+
+# undef utimensat
+
+/* If we have a native utimensat, but are compiling this file, then
+   utimensat was defined to rpl_utimensat by our replacement
+   sys/stat.h.  We assume the native version might fail with ENOSYS,
+   or succeed without properly affecting ctime (as is the case when
+   using newer glibc but older Linux kernel).  In this scenario,
+   rpl_utimensat checks whether the native version is usable, and
+   local_utimensat provides the fallback manipulation.  */
+
+static int local_utimensat (int, char const *, struct timespec const[2], int);
+# define AT_FUNC_NAME local_utimensat
+
+/* Like utimensat, but work around native bugs.  */
+
+int
+rpl_utimensat (int fd, char const *file, struct timespec const times[2],
+               int flag)
+{
+# if defined __linux__ || defined __sun
+  struct timespec ts[2];
+# endif
+
+  /* See comments in utimens.c for details.  */
+  static int utimensat_works_really; /* 0 = unknown, 1 = yes, -1 = no.  */
+  if (0 <= utimensat_works_really)
+    {
+      int result;
+# if defined __linux__ || defined __sun
+      struct stat st;
+      /* As recently as Linux kernel 2.6.32 (Dec 2009), several file
+         systems (xfs, ntfs-3g) have bugs with a single UTIME_OMIT,
+         but work if both times are either explicitly specified or
+         UTIME_NOW.  Work around it with a preparatory [l]stat prior
+         to calling utimensat; fortunately, there is not much timing
+         impact due to the extra syscall even on file systems where
+         UTIME_OMIT would have worked.
+
+         The same bug occurs in Solaris 11.1 (Apr 2013).
+
+         FIXME: Simplify this in 2024, when these file system bugs are
+         no longer common on Gnulib target platforms.  */
+      if (times && (times[0].tv_nsec == UTIME_OMIT
+                    || times[1].tv_nsec == UTIME_OMIT))
+        {
+          if (fstatat (fd, file, &st, flag))
+            return -1;
+          if (times[0].tv_nsec == UTIME_OMIT && times[1].tv_nsec == UTIME_OMIT)
+            return 0;
+          if (times[0].tv_nsec == UTIME_OMIT)
+            ts[0] = get_stat_atime (&st);
+          else
+            ts[0] = times[0];
+          if (times[1].tv_nsec == UTIME_OMIT)
+            ts[1] = get_stat_mtime (&st);
+          else
+            ts[1] = times[1];
+          times = ts;
+        }
+#  ifdef __hppa__
+      /* Linux kernel 2.6.22.19 on hppa does not reject invalid tv_nsec
+         values.  */
+      else if (times
+               && ((times[0].tv_nsec != UTIME_NOW
+                    && ! (0 <= times[0].tv_nsec
+                          && times[0].tv_nsec < TIMESPEC_HZ))
+                   || (times[1].tv_nsec != UTIME_NOW
+                       && ! (0 <= times[1].tv_nsec
+                             && times[1].tv_nsec < TIMESPEC_HZ))))
+        {
+          errno = EINVAL;
+          return -1;
+        }
+#  endif
+# endif
+      result = utimensat (fd, file, times, flag);
+      /* Linux kernel 2.6.25 has a bug where it returns EINVAL for
+         UTIME_NOW or UTIME_OMIT with non-zero tv_sec, which
+         local_utimensat works around.  Meanwhile, EINVAL for a bad
+         flag is indeterminate whether the native utimensat works, but
+         local_utimensat will also reject it.  */
+      if (result == -1 && errno == EINVAL && (flag & ~AT_SYMLINK_NOFOLLOW))
+        return result;
+      if (result == 0 || (errno != ENOSYS && errno != EINVAL))
+        {
+          utimensat_works_really = 1;
+          return result;
+        }
+    }
+  /* No point in trying openat/futimens, since on Linux, futimens is
+     implemented with the same syscall as utimensat.  Only avoid the
+     native utimensat due to an ENOSYS failure; an EINVAL error was
+     data-dependent, and the next caller may pass valid data.  */
+  if (0 <= utimensat_works_really && errno == ENOSYS)
+    utimensat_works_really = -1;
+  return local_utimensat (fd, file, times, flag);
+}
+
+#else /* !HAVE_UTIMENSAT */
+
+# define AT_FUNC_NAME utimensat
+
+#endif /* !HAVE_UTIMENSAT */
+
+/* Set the access and modification timestamps of FILE to be
+   TIMESPEC[0] and TIMESPEC[1], respectively; relative to directory
+   FD.  If flag is AT_SYMLINK_NOFOLLOW, change the times of a symlink,
+   or fail with ENOSYS if not possible.  If TIMESPEC is null, set the
+   timestamps to the current time.  If possible, do it without
+   changing the working directory.  Otherwise, resort to using
+   save_cwd/fchdir, then utimens/restore_cwd.  If either the save_cwd
+   or the restore_cwd fails, then give a diagnostic and exit nonzero.
+   Return 0 on success, -1 (setting errno) on failure.  */
+
+/* AT_FUNC_NAME is now utimensat or local_utimensat.  */
+#define AT_FUNC_F1 lutimens
+#define AT_FUNC_F2 utimens
+#define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
+#define AT_FUNC_POST_FILE_PARAM_DECLS , struct timespec const ts[2], int flag
+#define AT_FUNC_POST_FILE_ARGS        , ts
+#include "at-func.c"
+#undef AT_FUNC_NAME
+#undef AT_FUNC_F1
+#undef AT_FUNC_F2
+#undef AT_FUNC_USE_F1_COND
+#undef AT_FUNC_POST_FILE_PARAM_DECLS
+#undef AT_FUNC_POST_FILE_ARGS