2012-12-12 Daniel Colascione <dancol@dancol.org>

	* unexcw.c (fixup_executable): use posix_fallocate to ensure that
	the dumped Emacs is not a sparse file, greatly improving Cygwin
	"make bootstrap" performance.

2 files changed, 19 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 3311f7c33a3..d19b7be7395 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2012-12-12  Daniel Colascione  <dancol@dancol.org>
+
+        * unexcw.c (fixup_executable): use posix_fallocate to ensure that
+        the dumped Emacs is not a sparse file, greatly improving Cygwin
+        "make bootstrap" performance.
+
 2012-12-11  Michael Albinus  <michael.albinus@gmx.de>
 
         * inotify.c (inotify_callback): Generate an Emacs event for every
diff --git a/src/unexcw.c b/src/unexcw.c
index 8c5d574530d..7d1a72e0009 100644
--- a/src/unexcw.c
+++ b/src/unexcw.c
@@ -183,6 +183,19 @@ fixup_executable (int fd)
                 exe_header->file_optional_header.FileAlignment *
                 exe_header->file_optional_header.FileAlignment;
 
+              /* Make sure the generated bootstrap binary isn't
+               * sparse.  NT doesn't use a file cache for sparse
+               * executables, so if we bootstrap Emacs using a sparse
+               * bootstrap-emacs.exe, bootstrap takes about twenty
+               * times longer than it would otherwise.  */
+
+              ret = posix_fallocate (fd,
+                                     ( exe_header->section_header[i].s_scnptr +
+                                       exe_header->section_header[i].s_size ),
+                                     1);
+
+              assert (ret != -1);
+
               ret =
                 lseek (fd,
                        (long) (exe_header->section_header[i].s_scnptr +