Re: [gold] RFC: Add options for controlling mmap and fallocate of output file

[Cary Coutant <ccoutant at google dot com>]

> I think you need a test for fallocate.

Here's a revised patch...

-cary


2012-06-06  Cary Coutant  <ccoutant@google.com>

	* configure.ac: Add check for fallocate.
	* configure: Regenerate.
	* config.in: Regenerate.

	* options.h (class General_options): Add --mmap-output-file and
	--posix-fallocate options.
	* output.cc: (posix_fallocate): Remove; replace with...
	(gold_fallocate): New function.
	(Output_file::map_no_anonymous): Call gold_fallocate.
	(Output_file::map): Check --mmap-output-file option.


commit 3688e1b5f721139bcb0e6acc5af036c8a1a25a60
Author: Cary Coutant <ccoutant@google.com>
Date:   Tue Jun 5 17:00:35 2012 -0700

    Add --mmap-output-file and --posix-fallocate options.

diff --git a/gold/configure.ac b/gold/configure.ac
index a2c4875..fdea629 100644
--- a/gold/configure.ac
+++ b/gold/configure.ac
@@ -499,7 +499,7 @@ AC_LANG_PUSH(C++)
 AC_CHECK_HEADERS(tr1/unordered_set tr1/unordered_map)
 AC_CHECK_HEADERS(ext/hash_map ext/hash_set)
 AC_CHECK_HEADERS(byteswap.h)
-AC_CHECK_FUNCS(mallinfo posix_fallocate readv sysconf times)
+AC_CHECK_FUNCS(mallinfo posix_fallocate fallocate readv sysconf times)
 AC_CHECK_DECLS([basename, ffs, asprintf, vasprintf, snprintf,
vsnprintf, strverscmp, strndup, memmem])

 # Use of ::std::tr1::unordered_map::rehash causes undefined symbols
diff --git a/gold/options.h b/gold/options.h
index b244bd5..6463b80 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -889,6 +889,10 @@ class General_options
   DEFINE_string(m, options::EXACTLY_ONE_DASH, 'm', "",
                 N_("Set GNU linker emulation; obsolete"), N_("EMULATION"));

+  DEFINE_bool(mmap_output_file, options::TWO_DASHES, '\0', true,
+              N_("Map the output file for writing (default)."),
+              N_("Do not map the output file for writing."));
+
   DEFINE_bool(print_map, options::TWO_DASHES, 'M', false,
 	      N_("Write map file on standard output"), NULL);
   DEFINE_string(Map, options::ONE_DASH, '\0', NULL, N_("Write map file"),
@@ -939,6 +943,11 @@ class General_options
                  N_("Pass an option to the plugin"), N_("OPTION"));
 #endif

+  DEFINE_bool(posix_fallocate, options::TWO_DASHES, '\0', true,
+              N_("Use posix_fallocate to reserve space in the output file"
+		 " (default)."),
+              N_("Use fallocate or ftruncate to reserve space."));
+
   DEFINE_bool(preread_archive_symbols, options::TWO_DASHES, '\0', false,
               N_("Preread archive symbols when multi-threaded"), NULL);

diff --git a/gold/output.cc b/gold/output.cc
index 2236916..99890eb 100644
--- a/gold/output.cc
+++ b/gold/output.cc
@@ -111,20 +111,6 @@ extern "C" void *gold_mremap(void *, size_t, size_t, int);
 # define MREMAP_MAYMOVE 1
 #endif

-#ifndef HAVE_POSIX_FALLOCATE
-// A dummy, non general, version of posix_fallocate.  Here we just set
-// the file size and hope that there is enough disk space.  FIXME: We
-// could allocate disk space by walking block by block and writing a
-// zero byte into each block.
-static int
-posix_fallocate(int o, off_t offset, off_t len)
-{
-  if (ftruncate(o, offset + len) < 0)
-    return errno;
-  return 0;
-}
-#endif // !defined(HAVE_POSIX_FALLOCATE)
-
 // Mingw does not have S_ISLNK.
 #ifndef S_ISLNK
 # define S_ISLNK(mode) 0
@@ -133,6 +119,27 @@ posix_fallocate(int o, off_t offset, off_t len)
 namespace gold
 {

+// A wrapper around posix_fallocate.  If we don't have posix_fallocate,
+// or the --no-posix-fallocate option is set, we try the fallocate
+// system call directly.  If that fails, we use ftruncate to set
+// the file size and hope that there is enough disk space.
+
+static int
+gold_fallocate(int o, off_t offset, off_t len)
+{
+#ifdef HAVE_POSIX_FALLOCATE
+  if (parameters->options().posix_fallocate())
+    return ::posix_fallocate(o, offset, len);
+#endif // defined(HAVE_POSIX_FALLOCATE)
+#ifdef HAVE_FALLOCATE
+  if (::fallocate(o, 0, offset, len) == 0)
+    return 0;
+#endif // defined(HAVE_FALLOCATE)
+  if (::ftruncate(o, offset + len) < 0)
+    return errno;
+  return 0;
+}
+
 // Output_data variables.

 bool Output_data::allocated_sizes_are_fixed;
@@ -5014,7 +5021,7 @@ Output_file::map_no_anonymous(bool writable)
   // but that would be a more significant performance hit.
   if (writable)
     {
-      int err = ::posix_fallocate(o, 0, this->file_size_);
+      int err = gold_fallocate(o, 0, this->file_size_);
       if (err != 0)
        gold_fatal(_("%s: %s"), this->name_, strerror(err));
     }
@@ -5041,7 +5048,8 @@ Output_file::map_no_anonymous(bool writable)
 void
 Output_file::map()
 {
-  if (this->map_no_anonymous(true))
+  if (parameters->options().mmap_output_file()
+      && this->map_no_anonymous(true))
     return;

   // The mmap call might fail because of file system issues: the file