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, 64 insertions, 0 deletions

diff --git a/lib/openat-priv.h b/lib/openat-priv.h
new file mode 100644
index 00000000000..829cf7d0855
--- /dev/null
+++ b/lib/openat-priv.h
@@ -0,0 +1,64 @@
+/* Internals for openat-like functions.
+
+   Copyright (C) 2005-2006, 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 Jim Meyering */
+
+#ifndef _GL_HEADER_OPENAT_PRIV
+#define _GL_HEADER_OPENAT_PRIV
+
+#include <errno.h>
+#include <limits.h>
+#include <stdlib.h>
+
+/* Maximum number of bytes that it is safe to allocate as a single
+   array on the stack, and that is known as a compile-time constant.
+   The assumption is that we'll touch the array very quickly, or a
+   temporary very near the array, provoking an out-of-memory trap.  On
+   some operating systems, there is only one guard page for the stack,
+   and a page size can be as small as 4096 bytes.  Subtract 64 in the
+   hope that this will let the compiler touch a nearby temporary and
+   provoke a trap.  */
+#define SAFER_ALLOCA_MAX (4096 - 64)
+
+#define SAFER_ALLOCA(m) ((m) < SAFER_ALLOCA_MAX ? (m) : SAFER_ALLOCA_MAX)
+
+#if defined PATH_MAX
+# define OPENAT_BUFFER_SIZE SAFER_ALLOCA (PATH_MAX)
+#elif defined _XOPEN_PATH_MAX
+# define OPENAT_BUFFER_SIZE SAFER_ALLOCA (_XOPEN_PATH_MAX)
+#else
+# define OPENAT_BUFFER_SIZE SAFER_ALLOCA (1024)
+#endif
+
+char *openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file);
+
+/* Trying to access a BUILD_PROC_NAME file will fail on systems without
+   /proc support, and even on systems *with* ProcFS support.  Return
+   nonzero if the failure may be legitimate, e.g., because /proc is not
+   readable, or the particular .../fd/N directory is not present.  */
+#define EXPECTED_ERRNO(Errno)                   \
+  ((Errno) == ENOTDIR || (Errno) == ENOENT      \
+   || (Errno) == EPERM || (Errno) == EACCES     \
+   || (Errno) == ENOSYS /* Solaris 8 */         \
+   || (Errno) == EOPNOTSUPP /* FreeBSD */)
+
+/* Wrapper function shared among linkat and renameat.  */
+int at_func2 (int fd1, char const *file1,
+              int fd2, char const *file2,
+              int (*func) (char const *file1, char const *file2));
+
+#endif /* _GL_HEADER_OPENAT_PRIV */