Improve make-temp-file performance on local files

For the motivation behind this patch, please see Bug#28023 and:
http://emacshorrors.com/posts/make-temp-name.html
Although, given the recent changes to Tramp, the related security
problem in make-temp-file is already fixed, make-temp-file still has
several unnecessary system calls.  In the typical case on GNU/Linux,
this patch replaces 8 syscalls (symlink, open, close, readlinkat, uname,
getpid, unlink, umask) by 2 (open, close).
* admin/merge-gnulib (GNULIB_MODULES): Add tempname, now
that Emacs is using it directly.
* configure.ac (AUTO_DEPEND): Remove AC_SYS_LONG_FILE_NAMES;
no longer needed.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* lisp/files.el (files--make-magic-temp-file): Rename from
make-temp-file.
(make-temp-file): Use make-temp-file-internal for
non-magic file names.
* src/fileio.c: Include tempname.h.
(make_temp_name_tbl, make_temp_name_count)
(make_temp_name_count_initialized_p, make_temp_name): Remove.
(Fmake_temp_file_internal): New function.
(Fmake_temp_name): Use it.
* src/filelock.c (get_boot_time): Use Fmake_temp_file_internal
instead of make_temp_name.

10 files changed, 63 insertions, 157 deletions

diff --git a/admin/CPP-DEFINES b/admin/CPP-DEFINES
index cead305aee1..10b558d1ada 100644
--- a/admin/CPP-DEFINES
+++ b/admin/CPP-DEFINES
@@ -205,7 +205,6 @@ HAVE_LIBXML2
 HAVE_LIBXMU
 HAVE_LOCALTIME_R
 HAVE_LOCAL_SOCKETS
-HAVE_LONG_FILE_NAMES
 HAVE_LONG_LONG_INT
 HAVE_LRAND48
 HAVE_LSTAT
diff --git a/admin/merge-gnulib b/admin/merge-gnulib
index a16d7fa53ea..7eca64305de 100755
--- a/admin/merge-gnulib
+++ b/admin/merge-gnulib
@@ -39,8 +39,8 @@ GNULIB_MODULES='
   manywarnings memrchr minmax mkostemp mktime nstrftime
   pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat
   sig2str socklen stat-time std-gnu11 stdalign stddef stdio
-  stpcpy strtoimax symlink sys_stat
-  sys_time time time_r time_rz timegm timer-time timespec-add timespec-sub
+  stpcpy strtoimax symlink sys_stat sys_time
+  tempname time time_r time_rz timegm timer-time timespec-add timespec-sub
   update-copyright unlocked-io utimens
   vla warnings
 '
diff --git a/configure.ac b/configure.ac
index 9f80620a807..86d5b3e94f9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1779,9 +1779,6 @@ if test "$GCC" = yes && test "$ac_enable_autodepend" = yes; then
 fi
 AC_SUBST(AUTO_DEPEND)
 
-dnl checks for operating system services
-AC_SYS_LONG_FILE_NAMES
-
 #### Choose a window system.
 
 ## We leave window_system equal to none if
diff --git a/lib/gnulib.mk.in b/lib/gnulib.mk.in
index c5df3f42e47..30986b4ed7f 100644
--- a/lib/gnulib.mk.in
+++ b/lib/gnulib.mk.in
@@ -21,7 +21,7 @@
 # the same distribution terms as the rest of that program.
 #
 # Generated by gnulib-tool.
-# Reproduce by: gnulib-tool --import --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=close --avoid=dup --avoid=fchdir --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=open --avoid=openat-die --avoid=opendir --avoid=raise --avoid=save-cwd --avoid=select --avoid=setenv --avoid=sigprocmask --avoid=stat --avoid=stdarg --avoid=stdbool --avoid=threadlib --avoid=tzset --avoid=unsetenv --avoid=utime --avoid=utime-h --gnu-make --makefile-name=gnulib.mk.in --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt binary-io byteswap c-ctype c-strcase careadlinkat close-stream count-leading-zeros count-one-bits count-trailing-zeros crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 d-type diffseq dtoastr dtotimespec dup2 environ execinfo explicit_bzero faccessat fcntl fcntl-h fdatasync fdopendir filemode filevercmp flexmember fstatat fsync getloadavg getopt-gnu gettime gettimeofday gitlog-to-changelog ignore-value intprops largefile lstat manywarnings memrchr minmax mkostemp mktime nstrftime pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat sig2str socklen stat-time std-gnu11 stdalign stddef stdio stpcpy strtoimax symlink sys_stat sys_time time time_r time_rz timegm timer-time timespec-add timespec-sub unlocked-io update-copyright utimens vla warnings
+# Reproduce by: gnulib-tool --import --lib=libgnu --source-base=lib --m4-base=m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --avoid=close --avoid=dup --avoid=fchdir --avoid=fstat --avoid=malloc-posix --avoid=msvc-inval --avoid=msvc-nothrow --avoid=open --avoid=openat-die --avoid=opendir --avoid=raise --avoid=save-cwd --avoid=select --avoid=setenv --avoid=sigprocmask --avoid=stat --avoid=stdarg --avoid=stdbool --avoid=threadlib --avoid=tzset --avoid=unsetenv --avoid=utime --avoid=utime-h --gnu-make --makefile-name=gnulib.mk.in --conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files alloca-opt binary-io byteswap c-ctype c-strcase careadlinkat close-stream count-leading-zeros count-one-bits count-trailing-zeros crypto/md5 crypto/sha1 crypto/sha256 crypto/sha512 d-type diffseq dtoastr dtotimespec dup2 environ execinfo explicit_bzero faccessat fcntl fcntl-h fdatasync fdopendir filemode filevercmp flexmember fstatat fsync getloadavg getopt-gnu gettime gettimeofday gitlog-to-changelog ignore-value intprops largefile lstat manywarnings memrchr minmax mkostemp mktime nstrftime pipe2 pselect pthread_sigmask putenv qcopy-acl readlink readlinkat sig2str socklen stat-time std-gnu11 stdalign stddef stdio stpcpy strtoimax symlink sys_stat sys_time tempname time time_r time_rz timegm timer-time timespec-add timespec-sub unlocked-io update-copyright utimens vla warnings
 
 
 MOSTLYCLEANFILES += core *.stackdump
@@ -904,7 +904,6 @@ gl_GNULIB_ENABLED_euidaccess = @gl_GNULIB_ENABLED_euidaccess@
 gl_GNULIB_ENABLED_getdtablesize = @gl_GNULIB_ENABLED_getdtablesize@
 gl_GNULIB_ENABLED_getgroups = @gl_GNULIB_ENABLED_getgroups@
 gl_GNULIB_ENABLED_strtoll = @gl_GNULIB_ENABLED_strtoll@
-gl_GNULIB_ENABLED_tempname = @gl_GNULIB_ENABLED_tempname@
 gl_LIBOBJS = @gl_LIBOBJS@
 gl_LTLIBOBJS = @gl_LTLIBOBJS@
 gltests_LIBOBJS = @gltests_LIBOBJS@
@@ -2701,10 +2700,8 @@ endif
 ## begin gnulib module tempname
 ifeq (,$(OMIT_GNULIB_MODULE_tempname))
 
-ifneq (,$(gl_GNULIB_ENABLED_tempname))
 libgnu_a_SOURCES += tempname.c
 
-endif
 EXTRA_DIST += tempname.h
 
 endif
diff --git a/lisp/files.el b/lisp/files.el
index 0fe7f9c522a..19573cdf7b2 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -1407,6 +1407,15 @@ You can then use `write-region' to write new data into the file.
 If DIR-FLAG is non-nil, create a new empty directory instead of a file.
 
 If SUFFIX is non-nil, add that at the end of the file name."
+  (let ((absolute-prefix (expand-file-name prefix temporary-file-directory)))
+    (if (find-file-name-handler absolute-prefix 'write-region)
+        (files--make-magic-temp-file prefix dir-flag suffix)
+      (make-temp-file-internal absolute-prefix
+                               (if dir-flag t) (or suffix "")))))
+
+(defun files--make-magic-temp-file (prefix &optional dir-flag suffix)
+  "Implement (make-temp-file PREFIX DIR-FLAG SUFFIX).
+This implementation works on magic file names."
   ;; Create temp files with strict access rights.  It's easy to
   ;; loosen them later, whereas it's impossible to close the
   ;; time-window of loose permissions otherwise.
diff --git a/m4/gnulib-comp.m4 b/m4/gnulib-comp.m4
index 69d77229bf7..d1089860e19 100644
--- a/m4/gnulib-comp.m4
+++ b/m4/gnulib-comp.m4
@@ -387,6 +387,7 @@ AC_DEFUN([gl_INIT],
   AC_PROG_MKDIR_P
   gl_SYS_TYPES_H
   AC_PROG_MKDIR_P
+  gl_FUNC_GEN_TEMPNAME
   gl_HEADER_TIME_H
   gl_TIME_R
   if test $HAVE_LOCALTIME_R = 0 || test $REPLACE_LOCALTIME_R = 1; then
@@ -424,7 +425,6 @@ AC_DEFUN([gl_INIT],
   gl_gnulib_enabled_03e0aaad4cb89ca757653bd367a6ccb7=false
   gl_gnulib_enabled_6099e9737f757db36c47fa9d9f02e88c=false
   gl_gnulib_enabled_strtoll=false
-  gl_gnulib_enabled_tempname=false
   gl_gnulib_enabled_682e609604ccaac6be382e4ee3a4eaec=false
   func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b ()
   {
@@ -560,13 +560,6 @@ AC_DEFUN([gl_INIT],
       gl_gnulib_enabled_strtoll=true
     fi
   }
-  func_gl_gnulib_m4code_tempname ()
-  {
-    if ! $gl_gnulib_enabled_tempname; then
-      gl_FUNC_GEN_TEMPNAME
-      gl_gnulib_enabled_tempname=true
-    fi
-  }
   func_gl_gnulib_m4code_682e609604ccaac6be382e4ee3a4eaec ()
   {
     if ! $gl_gnulib_enabled_682e609604ccaac6be382e4ee3a4eaec; then
@@ -612,9 +605,6 @@ AC_DEFUN([gl_INIT],
   if test $REPLACE_LSTAT = 1; then
     func_gl_gnulib_m4code_dosname
   fi
-  if test $HAVE_MKOSTEMP = 0; then
-    func_gl_gnulib_m4code_tempname
-  fi
   if test $HAVE_READLINKAT = 0; then
     func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b
   fi
@@ -644,7 +634,6 @@ AC_DEFUN([gl_INIT],
   AM_CONDITIONAL([gl_GNULIB_ENABLED_03e0aaad4cb89ca757653bd367a6ccb7], [$gl_gnulib_enabled_03e0aaad4cb89ca757653bd367a6ccb7])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_6099e9737f757db36c47fa9d9f02e88c], [$gl_gnulib_enabled_6099e9737f757db36c47fa9d9f02e88c])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_strtoll], [$gl_gnulib_enabled_strtoll])
-  AM_CONDITIONAL([gl_GNULIB_ENABLED_tempname], [$gl_gnulib_enabled_tempname])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_682e609604ccaac6be382e4ee3a4eaec], [$gl_gnulib_enabled_682e609604ccaac6be382e4ee3a4eaec])
   # End of code from modules
   m4_ifval(gl_LIBSOURCES_LIST, [
diff --git a/src/buffer.c b/src/buffer.c
index 0d0f43e937b..2d508f35cf6 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1085,7 +1085,6 @@ is first appended to NAME, to speed up finding a non-existent buffer.  */)
     genbase = name;
   else
     {
-      /* Note fileio.c:make_temp_name does random differently.  */
       char number[sizeof "-999999"];
       int i = XFASTINT (Frandom (make_number (999999)));
       AUTO_STRING_WITH_LEN (lnumber, number, sprintf (number, "-%d", i));
diff --git a/src/fileio.c b/src/fileio.c
index 31fd84512e1..b7e3b71a475 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -97,6 +97,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <allocator.h>
 #include <careadlinkat.h>
 #include <stat-time.h>
+#include <tempname.h>
 
 #include <binary-io.h>
 
@@ -655,149 +656,67 @@ In Unix-syntax, this function just removes the final slash.  */)
   return val;
 }
 
-static const char make_temp_name_tbl[64] =
-{
-  'A','B','C','D','E','F','G','H',
-  'I','J','K','L','M','N','O','P',
-  'Q','R','S','T','U','V','W','X',
-  'Y','Z','a','b','c','d','e','f',
-  'g','h','i','j','k','l','m','n',
-  'o','p','q','r','s','t','u','v',
-  'w','x','y','z','0','1','2','3',
-  '4','5','6','7','8','9','-','_'
-};
-
-static unsigned make_temp_name_count, make_temp_name_count_initialized_p;
-
-/* Value is a temporary file name starting with PREFIX, a string.
+DEFUN ("make-temp-file-internal", Fmake_temp_file_internal,
+       Smake_temp_file_internal, 3, 3, 0,
+       doc: /* Generate a new file whose name starts with PREFIX, a string.
+Return the name of the generated file.  If DIR-FLAG is zero, do not
+create the file, just its name.  Otherwise, if DIR-FLAG is non-nil,
+create an empty directory.  The file name should end in SUFFIX.
 
-   The Emacs process number forms part of the result, so there is
-   no danger of generating a name being used by another process.
-   In addition, this function makes an attempt to choose a name
-   which has no existing file.  To make this work, PREFIX should be
-   an absolute file name.
+Signal an error if the file could not be created.
 
-   BASE64_P means add the pid as 3 characters in base64
-   encoding.  In this case, 6 characters will be added to PREFIX to
-   form the file name.  Otherwise, if Emacs is running on a system
-   with long file names, add the pid as a decimal number.
-
-   This function signals an error if no unique file name could be
-   generated.  */
-
-Lisp_Object
-make_temp_name (Lisp_Object prefix, bool base64_p)
+This function does not grok magic file names.  */)
+  (Lisp_Object prefix, Lisp_Object dir_flag, Lisp_Object suffix)
 {
-  Lisp_Object val, encoded_prefix;
-  ptrdiff_t len;
-  printmax_t pid;
-  char *p, *data;
-  char pidbuf[INT_BUFSIZE_BOUND (printmax_t)];
-  int pidlen;
-
-  CHECK_STRING (prefix);
-
-  /* VAL is created by adding 6 characters to PREFIX.  The first
-     three are the PID of this process, in base 64, and the second
-     three are incremented if the file already exists.  This ensures
-     262144 unique file names per PID per PREFIX.  */
-
-  pid = getpid ();
-
-  if (base64_p)
-    {
-      pidbuf[0] = make_temp_name_tbl[pid & 63], pid >>= 6;
-      pidbuf[1] = make_temp_name_tbl[pid & 63], pid >>= 6;
-      pidbuf[2] = make_temp_name_tbl[pid & 63], pid >>= 6;
-      pidlen = 3;
-    }
-  else
+  bool make_temp_name = EQ (dir_flag, make_number (0));
+  CHECK_STRING (suffix);
+  if (!make_temp_name)
+    prefix = Fexpand_file_name (prefix, Vtemporary_file_directory);
+
+  Lisp_Object encoded_prefix = ENCODE_FILE (prefix);
+  Lisp_Object encoded_suffix = ENCODE_FILE (suffix);
+  ptrdiff_t prefix_len = SBYTES (encoded_prefix);
+  ptrdiff_t suffix_len = SBYTES (encoded_suffix);
+  if (INT_MAX < suffix_len)
+    args_out_of_range (prefix, suffix);
+  int nX = 6;
+  Lisp_Object val = make_uninit_string (prefix_len + nX + suffix_len);
+  char *data = SSDATA (val);
+  memcpy (data, SSDATA (encoded_prefix), prefix_len);
+  memset (data + prefix_len, 'X', nX);
+  memcpy (data + prefix_len + nX, SSDATA (encoded_suffix), suffix_len);
+  int kind = (NILP (dir_flag) ? GT_FILE
+              : make_temp_name ? GT_NOCREATE
+              : GT_DIR);
+  int fd = gen_tempname (data, suffix_len, O_BINARY | O_CLOEXEC, kind);
+  if (fd < 0 || (NILP (dir_flag) && emacs_close (fd) != 0))
     {
-#ifdef HAVE_LONG_FILE_NAMES
-      pidlen = sprintf (pidbuf, "%"pMd, pid);
-#else
-      pidbuf[0] = make_temp_name_tbl[pid & 63], pid >>= 6;
-      pidbuf[1] = make_temp_name_tbl[pid & 63], pid >>= 6;
-      pidbuf[2] = make_temp_name_tbl[pid & 63], pid >>= 6;
-      pidlen = 3;
-#endif
-    }
-
-  encoded_prefix = ENCODE_FILE (prefix);
-  len = SBYTES (encoded_prefix);
-  val = make_uninit_string (len + 3 + pidlen);
-  data = SSDATA (val);
-  memcpy (data, SSDATA (encoded_prefix), len);
-  p = data + len;
-
-  memcpy (p, pidbuf, pidlen);
-  p += pidlen;
-
-  /* Here we try to minimize useless stat'ing when this function is
-     invoked many times successively with the same PREFIX.  We achieve
-     this by initializing count to a random value, and incrementing it
-     afterwards.
-
-     We don't want make-temp-name to be called while dumping,
-     because then make_temp_name_count_initialized_p would get set
-     and then make_temp_name_count would not be set when Emacs starts.  */
-
-  if (!make_temp_name_count_initialized_p)
-    {
-      make_temp_name_count = time (NULL);
-      make_temp_name_count_initialized_p = 1;
-    }
-
-  while (1)
-    {
-      unsigned num = make_temp_name_count;
-
-      p[0] = make_temp_name_tbl[num & 63], num >>= 6;
-      p[1] = make_temp_name_tbl[num & 63], num >>= 6;
-      p[2] = make_temp_name_tbl[num & 63], num >>= 6;
-
-      /* Poor man's congruential RN generator.  Replace with
-         ++make_temp_name_count for debugging.  */
-      make_temp_name_count += 25229;
-      make_temp_name_count %= 225307;
-
-      if (!check_existing (data))
+      static char const kind_message[][32] =
         {
-          /* We want to return only if errno is ENOENT.  */
-          if (errno == ENOENT)
-            return DECODE_FILE (val);
-          else
-            /* The error here is dubious, but there is little else we
-               can do.  The alternatives are to return nil, which is
-               as bad as (and in many cases worse than) throwing the
-               error, or to ignore the error, which will likely result
-               in looping through 225307 stat's, which is not only
-               dog-slow, but also useless since eventually nil would
-               have to be returned anyway.  */
-            report_file_error ("Cannot create temporary name for prefix",
-                               prefix);
-          /* not reached */
-        }
+          [GT_FILE] = "Creating file with prefix",
+          [GT_DIR] = "Creating directory with prefix",
+          [GT_NOCREATE] = "Creating file name with prefix"
+        };
+      report_file_error (kind_message[kind], prefix);
     }
+  return DECODE_FILE (val);
 }
 
 
 DEFUN ("make-temp-name", Fmake_temp_name, Smake_temp_name, 1, 1, 0,
        doc: /* Generate temporary file name (string) starting with PREFIX (a string).
-The Emacs process number forms part of the result, so there is no
-danger of generating a name being used by another Emacs process
-\(so long as only a single host can access the containing directory...).
 
 This function tries to choose a name that has no existing file.
 For this to work, PREFIX should be an absolute file name, and PREFIX
 and the returned string should both be non-magic.
 
-There is a race condition between calling `make-temp-name' and creating the
-file, which opens all kinds of security holes.  For that reason, you should
-normally use `make-temp-file' instead.  */)
+There is a race condition between calling `make-temp-name' and
+later creating the file, which opens all kinds of security holes.
+For that reason, you should normally use `make-temp-file' instead.  */)
   (Lisp_Object prefix)
 {
-  return make_temp_name (prefix, 0);
+  return Fmake_temp_file_internal (prefix, make_number (0),
+                                   empty_unibyte_string);
 }
 
 DEFUN ("expand-file-name", Fexpand_file_name, Sexpand_file_name, 1, 2, 0,
@@ -6168,6 +6087,7 @@ This includes interactive calls to `delete-file' and
   defsubr (&Sfile_name_as_directory);
   defsubr (&Sdirectory_name_p);
   defsubr (&Sdirectory_file_name);
+  defsubr (&Smake_temp_file_internal);
   defsubr (&Smake_temp_name);
   defsubr (&Sexpand_file_name);
   defsubr (&Ssubstitute_in_file_name);
diff --git a/src/filelock.c b/src/filelock.c
index dd8cb28c425..3d6941695ae 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -206,14 +206,11 @@ get_boot_time (void)
                                             WTMP_FILE, counter);
           if (! NILP (Ffile_exists_p (tempname)))
             {
-              /* The utmp functions on mescaline.gnu.org accept only
-                 file names up to 8 characters long.  Choose a 2
-                 character long prefix, and call make_temp_file with
-                 second arg non-zero, so that it will add not more
-                 than 6 characters to the prefix.  */
-              filename = Fexpand_file_name (build_string ("wt"),
-                                            Vtemporary_file_directory);
-              filename = make_temp_name (filename, 1);
+              /* The utmp functions on older systems accept only file
+                 names up to 8 bytes long.  Choose a 2 byte prefix, so
+                 the 6-byte suffix does not make the name too long.  */
+              filename = Fmake_temp_file_internal (build_string ("wt"), Qnil,
+                                                   empty_unibyte_string);
               CALLN (Fcall_process, build_string ("gzip"), Qnil,
                      list2 (QCfile, filename), Qnil,
                      build_string ("-cd"), tempname);
diff --git a/src/lisp.h b/src/lisp.h
index 25be5c0ceea..48cf3b30709 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4014,7 +4014,6 @@ extern bool file_directory_p (const char *);
 extern bool file_accessible_directory_p (Lisp_Object);
 extern void init_fileio (void);
 extern void syms_of_fileio (void);
-extern Lisp_Object make_temp_name (Lisp_Object, bool);
 
 /* Defined in search.c.  */
 extern void shrink_regexp_cache (void);