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, 61 insertions, 0 deletions

diff --git a/m4/fdopendir.m4 b/m4/fdopendir.m4
new file mode 100644
index 00000000000..b7be78324dc
--- /dev/null
+++ b/m4/fdopendir.m4
@@ -0,0 +1,61 @@
+# serial 10
+# See if we need to provide fdopendir.
+
+dnl Copyright (C) 2009-2013 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.
+
+# Written by Eric Blake.
+
+AC_DEFUN([gl_FUNC_FDOPENDIR],
+[
+  AC_REQUIRE([gl_DIRENT_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  dnl FreeBSD 7.3 has the function, but failed to declare it.
+  AC_CHECK_DECLS([fdopendir], [], [HAVE_DECL_FDOPENDIR=0], [[
+#include <dirent.h>
+    ]])
+  AC_CHECK_FUNCS_ONCE([fdopendir])
+  if test $ac_cv_func_fdopendir = no; then
+    HAVE_FDOPENDIR=0
+  else
+    AC_CACHE_CHECK([whether fdopendir works],
+      [gl_cv_func_fdopendir_works],
+      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <dirent.h>
+#include <fcntl.h>
+#include <unistd.h>
+#if !HAVE_DECL_FDOPENDIR
+extern
+# ifdef __cplusplus
+"C"
+# endif
+DIR *fdopendir (int);
+#endif
+]], [int result = 0;
+     int fd = open ("conftest.c", O_RDONLY);
+     if (fd < 0) result |= 1;
+     if (fdopendir (fd)) result |= 2;
+     if (close (fd)) result |= 4;
+     return result;])],
+         [gl_cv_func_fdopendir_works=yes],
+         [gl_cv_func_fdopendir_works=no],
+         [case "$host_os" in
+                    # Guess yes on glibc systems.
+            *-gnu*) gl_cv_func_fdopendir_works="guessing yes" ;;
+                    # If we don't know, assume the worst.
+            *)      gl_cv_func_fdopendir_works="guessing no" ;;
+          esac
+         ])])
+    case "$gl_cv_func_fdopendir_works" in
+      *yes) ;;
+      *)
+        REPLACE_FDOPENDIR=1
+        ;;
+    esac
+  fi
+])