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, 8 insertions, 10 deletions

diff --git a/src/filelock.c b/src/filelock.c
index f21240f8340..228fe98e8c7 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -390,12 +390,14 @@ current_lock_owner (lock_info_type *owner, char *lfname)
   lock_info_type local_owner;
   intmax_t n;
   char *at, *dot, *colon;
-  char readlink_buf[READLINK_BUFSIZE];
-  char *lfinfo = emacs_readlink (lfname, readlink_buf);
+  Lisp_Object lfinfo_object = emacs_readlinkat (AT_FDCWD, lfname);
+  char *lfinfo;
+  struct gcpro gcpro1;
 
   /* If nonexistent lock file, all is well; otherwise, got strange error. */
-  if (!lfinfo)
+  if (NILP (lfinfo_object))
     return errno == ENOENT ? 0 : -1;
+  lfinfo = SSDATA (lfinfo_object);
 
   /* Even if the caller doesn't want the owner info, we still have to
      read it to determine return value.  */
@@ -407,12 +409,9 @@ current_lock_owner (lock_info_type *owner, char *lfname)
   at = strrchr (lfinfo, '@');
   dot = strrchr (lfinfo, '.');
   if (!at || !dot)
-    {
-      if (lfinfo != readlink_buf)
-        xfree (lfinfo);
-      return -1;
-    }
+    return -1;
   len = at - lfinfo;
+  GCPRO1 (lfinfo_object);
   owner->user = xmalloc (len + 1);
   memcpy (owner->user, lfinfo, len);
   owner->user[len] = 0;
@@ -445,8 +444,7 @@ current_lock_owner (lock_info_type *owner, char *lfname)
   owner->host[len] = 0;
 
   /* We're done looking at the link info.  */
-  if (lfinfo != readlink_buf)
-    xfree (lfinfo);
+  UNGCPRO;
 
   /* On current host?  */
   if (STRINGP (Fsystem_name ())