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

2 files changed, 11 insertions, 4 deletions

diff --git a/admin/ChangeLog b/admin/ChangeLog
index 5da0bf0c67d..76ac11446a3 100644
--- a/admin/ChangeLog
+++ b/admin/ChangeLog
@@ -1,3 +1,10 @@
+2013-02-01  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Use fdopendir, fstatat and readlinkat, for efficiency (Bug#13539).
+        * merge-gnulib (GNULIB_MODULES): Add fdopendir, fstatat, readlinkat.
+        (GNULIB_TOOL_FLAGS): Do not avoid at-internal, openat-h.
+        Avoid dup, open, opendir.
+
 2013-01-15  Dmitry Antipov  <dmantipov@yandex.ru>
 
         * coccinelle/xsave.cocci: Semantic patch to adjust users of
diff --git a/admin/merge-gnulib b/admin/merge-gnulib
index f3509d98b85..e90e2e23b29 100755
--- a/admin/merge-gnulib
+++ b/admin/merge-gnulib
@@ -29,9 +29,9 @@ GNULIB_MODULES='
   alloca-opt c-ctype c-strcase
   careadlinkat close-stream crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512
   dtoastr dtotimespec dup2 environ execinfo faccessat
-  fcntl-h filemode getloadavg getopt-gnu gettime gettimeofday
+  fcntl-h fdopendir filemode fstatat getloadavg getopt-gnu gettime gettimeofday
   ignore-value intprops largefile lstat
-  manywarnings mktime pselect pthread_sigmask putenv readlink
+  manywarnings mktime pselect pthread_sigmask putenv readlink readlinkat
   sig2str socklen stat-time stdalign stdarg stdbool stdio
   strftime strtoimax strtoumax symlink sys_stat
   sys_time time timer-time timespec-add timespec-sub unsetenv utimens
@@ -39,10 +39,10 @@ GNULIB_MODULES='
 '
 
 GNULIB_TOOL_FLAGS='
-  --avoid=at-internal
+  --avoid=dup
   --avoid=errno --avoid=fchdir --avoid=fcntl --avoid=fstat
   --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow
-  --avoid=openat-die --avoid=openat-h
+  --avoid=open --avoid=openat-die --avoid=opendir
   --avoid=raise
   --avoid=save-cwd --avoid=select --avoid=sigprocmask --avoid=sys_types
   --avoid=threadlib