Use fdopendir, fstatat and readlinkat, for efficiency.

On my host, this speeds up directory-files-and-attributes by a
factor of 3, when applied to Emacs's src directory.
These functions are standardized by POSIX and are common these
days; fall back on a (slower) gnulib implementation if the host
is too old to supply them.
* .bzrignore: Add lib/dirent.h.
* lib/Makefile.am (libgnu_a_SOURCES): Add openat-die.c, save-cwd.c.
* lib/careadlinkat.c, lib/careadlinkat.h: Merge from gnulib,
incorporating: 2013-01-29 careadlinkat: do not provide careadlinkatcwd.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* lib/dirent.in.h, lib/fdopendir.c, lib/fstatat.c, lib/openat-priv.h:
* lib/openat-proc.c, lib/openat.h, m4/dirent_h.m4, m4/fdopendir.m4:
* m4/fstatat.m4: New files, from gnulib.
* lib/openat-die.c, lib/save-cwd.c, lib/save-cwd.h: New files.
These last three are specific to Emacs and are not copied from gnulib.
They are simpler than the gnulib versions and are tuned for Emacs.
* admin/merge-gnulib (GNULIB_MODULES): Add fdopendir, fstatat, readlinkat.
(GNULIB_TOOL_FLAGS): Do not avoid at-internal, openat-h.
Avoid dup, open, opendir.
* nt/inc/sys/stat.h (fstatat):
* nt/inc/unistd.h (readlinkat): New decls.
* src/conf_post.h (GNULIB_SUPPORT_ONLY_AT_FDCWD): Remove.
* src/dired.c: Include <fcntl.h>.
(open_directory): New function, which uses open and fdopendir
rather than opendir.  DOS_NT platforms still use opendir, though.
(directory_files_internal, file_name_completion): Use it.
(file_attributes): New function, with most of the old Ffile_attributes.
(directory_files_internal, Ffile_attributes): Use it.
(file_attributes, file_name_completion_stat): First arg is now fd,
not dir name.  All uses changed.  Use fstatat rather than lstat +
stat.
(file_attributes): Use emacs_readlinkat rather than Ffile_symlink_p.
* src/fileio.c: Include <allocator.h>, <careadlinkat.h>.
(emacs_readlinkat): New function, with much of the old
Ffile_symlink_p, but with an fd argument for speed.
It uses readlinkat rather than careadlinkatcwd, so that it
need not assume the working directory.
(Ffile_symlink_p): Use it.
* src/filelock.c (current_lock_owner): Use emacs_readlinkat
rather than emacs_readlink.
* src/lisp.h (emacs_readlinkat): New decl.
(READLINK_BUFSIZE, emacs_readlink): Remove.
* src/sysdep.c: Do not include <allocator.h>, <careadlinkat.h>.
(emacs_norealloc_allocator, emacs_readlink): Remove.
This stuff is moved to fileio.c.
* src/w32.c (fstatat, readlinkat): New functions.
(careadlinkat): Don't check that fd == AT_FDCWD.
(careadlinkatcwd): Remove; no longer needed.

Fixes: debbugs:13539

1 files changed, 135 insertions, 0 deletions

diff --git a/lib/fstatat.c b/lib/fstatat.c
new file mode 100644
index 00000000000..845c171fb45
--- /dev/null
+++ b/lib/fstatat.c
@@ -0,0 +1,135 @@
+/* Work around an fstatat bug on Solaris 9.
+
+   Copyright (C) 2006, 2009-2013 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/>.  */
+
+/* Written by Paul Eggert and Jim Meyering.  */
+
+/* If the user's config.h happens to include <sys/stat.h>, let it include only
+   the system's <sys/stat.h> here, so that orig_fstatat doesn't recurse to
+   rpl_fstatat.  */
+#define __need_system_sys_stat_h
+#include <config.h>
+
+/* Get the original definition of fstatat.  It might be defined as a macro.  */
+#include <sys/types.h>
+#include <sys/stat.h>
+#undef __need_system_sys_stat_h
+
+#if HAVE_FSTATAT
+static int
+orig_fstatat (int fd, char const *filename, struct stat *buf, int flags)
+{
+  return fstatat (fd, filename, buf, flags);
+}
+#endif
+
+/* Write "sys/stat.h" here, not <sys/stat.h>, otherwise OSF/1 5.1 DTK cc
+   eliminates this include because of the preliminary #include <sys/stat.h>
+   above.  */
+#include "sys/stat.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+
+#if HAVE_FSTATAT && HAVE_WORKING_FSTATAT_ZERO_FLAG
+
+# ifndef LSTAT_FOLLOWS_SLASHED_SYMLINK
+#  define LSTAT_FOLLOWS_SLASHED_SYMLINK 0
+# endif
+
+/* fstatat should always follow symbolic links that end in /, but on
+   Solaris 9 it doesn't if AT_SYMLINK_NOFOLLOW is specified.
+   Likewise, trailing slash on a non-directory should be an error.
+   These are the same problems that lstat.c and stat.c address, so
+   solve it in a similar way.
+
+   AIX 7.1 fstatat (AT_FDCWD, ..., 0) always fails, which is a bug.
+   Work around this bug if FSTATAT_AT_FDCWD_0_BROKEN is nonzero.  */
+
+int
+rpl_fstatat (int fd, char const *file, struct stat *st, int flag)
+{
+  int result = orig_fstatat (fd, file, st, flag);
+  size_t len;
+
+  if (LSTAT_FOLLOWS_SLASHED_SYMLINK || result != 0)
+    return result;
+  len = strlen (file);
+  if (flag & AT_SYMLINK_NOFOLLOW)
+    {
+      /* Fix lstat behavior.  */
+      if (file[len - 1] != '/' || S_ISDIR (st->st_mode))
+        return 0;
+      if (!S_ISLNK (st->st_mode))
+        {
+          errno = ENOTDIR;
+          return -1;
+        }
+      result = orig_fstatat (fd, file, st, flag & ~AT_SYMLINK_NOFOLLOW);
+    }
+  /* Fix stat behavior.  */
+  if (result == 0 && !S_ISDIR (st->st_mode) && file[len - 1] == '/')
+    {
+      errno = ENOTDIR;
+      return -1;
+    }
+  return result;
+}
+
+#else /* ! (HAVE_FSTATAT && HAVE_WORKING_FSTATAT_ZERO_FLAG) */
+
+/* On mingw, the gnulib <sys/stat.h> defines 'stat' as a function-like
+   macro; but using it in AT_FUNC_F2 causes compilation failure
+   because the preprocessor sees a use of a macro that requires two
+   arguments but is only given one.  Hence, we need an inline
+   forwarder to get past the preprocessor.  */
+static int
+stat_func (char const *name, struct stat *st)
+{
+  return stat (name, st);
+}
+
+/* Likewise, if there is no native 'lstat', then the gnulib
+   <sys/stat.h> defined it as stat, which also needs adjustment.  */
+# if !HAVE_LSTAT
+#  undef lstat
+#  define lstat stat_func
+# endif
+
+/* Replacement for Solaris' function by the same name.
+   <http://www.google.com/search?q=fstatat+site:docs.sun.com>
+   First, try to simulate it via l?stat ("/proc/self/fd/FD/FILE").
+   Failing that, simulate it via save_cwd/fchdir/(stat|lstat)/restore_cwd.
+   If either the save_cwd or the restore_cwd fails (relatively unlikely),
+   then give a diagnostic and exit nonzero.
+   Otherwise, this function works just like Solaris' fstatat.  */
+
+# define AT_FUNC_NAME fstatat
+# define AT_FUNC_F1 lstat
+# define AT_FUNC_F2 stat_func
+# define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
+# define AT_FUNC_POST_FILE_PARAM_DECLS , struct stat *st, int flag
+# define AT_FUNC_POST_FILE_ARGS        , st
+# 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
+
+#endif /* !HAVE_FSTATAT */