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

3 files changed, 9 insertions, 1 deletions

diff --git a/nt/ChangeLog b/nt/ChangeLog
index 8b8628db1e2..b2a481354bc 100644
--- a/nt/ChangeLog
+++ b/nt/ChangeLog
@@ -1,3 +1,9 @@
+2013-02-01  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Use fdopendir, fstatat and readlinkat, for efficiency (Bug#13539).
+        * inc/sys/stat.h (fstatat):
+        * inc/unistd.h (readlinkat): New decls.
+
 2013-01-28  Eli Zaretskii  <eliz@gnu.org>
 
         * inc/dirent.h (opendir): Update prototype.
diff --git a/nt/inc/sys/stat.h b/nt/inc/sys/stat.h
index 45689d24776..c356283c04b 100644
--- a/nt/inc/sys/stat.h
+++ b/nt/inc/sys/stat.h
@@ -110,6 +110,7 @@ _CRTIMP int __cdecl __MINGW_NOTHROW	fstat (int, struct stat*);
 _CRTIMP int __cdecl __MINGW_NOTHROW     chmod (const char*, int);
 _CRTIMP int __cdecl __MINGW_NOTHROW     stat (const char*, struct stat*);
 _CRTIMP int __cdecl __MINGW_NOTHROW     lstat (const char*, struct stat*);
+_CRTIMP int __cdecl __MINGW_NOTHROW     fstatat (int, char const *,
+                                                 struct stat *, int);
 
 #endif  /* INC_SYS_STAT_H_ */
-
diff --git a/nt/inc/unistd.h b/nt/inc/unistd.h
index 9c8a64d5ed2..3fd9289d83d 100644
--- a/nt/inc/unistd.h
+++ b/nt/inc/unistd.h
@@ -12,6 +12,7 @@
    and whose prototypes are usually found in unistd.h on POSIX
    platforms.  */
 extern ssize_t readlink (const char *, char *, size_t);
+extern ssize_t readlinkat (int, const char *, char *, size_t);
 extern int symlink (char const *, char const *);
 extern int setpgid (pid_t, pid_t);
 extern pid_t getpgrp (void);