Do not reopen temporary files

The current callers of mkostemp close the file descriptor and then
re-open it with fopen.  It seemed better to me to continue to use the
already-opened file descriptor, so this patch rearranges the code a
little in order to do so.  It takes care to ensure that the files are
only unlinked after the file descriptor in question is closed, as
before.

gdb/ChangeLog
2018-10-27  Tom Tromey  <tom@tromey.com>

	* unittests/scoped_fd-selftests.c (test_to_file): New function.
	(run_tests): Call test_to_file.
	* dwarf-index-write.c (write_psymtabs_to_index): Do not reopen
	temporary files.
	* common/scoped_fd.h (scoped_fd::to_file): New method.

4 files changed, 65 insertions, 29 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c6a5635..346d9c6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,13 @@
 2018-10-27  Tom Tromey  <tom@tromey.com>
 
+	* unittests/scoped_fd-selftests.c (test_to_file): New function.
+	(run_tests): Call test_to_file.
+	* dwarf-index-write.c (write_psymtabs_to_index): Do not reopen
+	temporary files.
+	* common/scoped_fd.h (scoped_fd::to_file): New method.
+
+2018-10-27  Tom Tromey  <tom@tromey.com>
+
 	* unittests/scoped_mmap-selftests.c (test_normal): Use
 	gdb_mkostemp_cloexec.
 	* unittests/scoped_fd-selftests.c (test_destroy, test_release):
diff --git a/gdb/common/scoped_fd.h b/gdb/common/scoped_fd.h
index c2125bd..d20e18a 100644
--- a/gdb/common/scoped_fd.h
+++ b/gdb/common/scoped_fd.h
@@ -21,6 +21,7 @@
 #define SCOPED_FD_H
 
 #include <unistd.h>
+#include "filestuff.h"
 
 /* A smart-pointer-like class to automatically close a file descriptor.  */
 
@@ -43,6 +44,18 @@ public:
     return fd;
   }
 
+  /* Like release, but return a gdb_file_up that owns the file
+     descriptor.  On success, this scoped_fd will be released.  On
+     failure, return NULL and leave this scoped_fd in possession of
+     the fd.  */
+  gdb_file_up to_file (const char *mode) noexcept
+  {
+    gdb_file_up result (fdopen (m_fd, mode));
+    if (result != nullptr)
+      m_fd = -1;
+    return result;
+  }
+
   int get () const noexcept
   {
     return m_fd;
diff --git a/gdb/dwarf-index-write.c b/gdb/dwarf-index-write.c
index e07bda9..8a4c1c7 100644
--- a/gdb/dwarf-index-write.c
+++ b/gdb/dwarf-index-write.c
@@ -1566,23 +1566,21 @@ write_psymtabs_to_index (struct dwarf2_per_objfile *dwarf2_per_objfile,
 			   ? INDEX5_SUFFIX : INDEX4_SUFFIX));
   gdb::char_vector filename_temp = make_temp_filename (filename);
 
-  gdb::optional<scoped_fd> out_file_fd
-    (gdb::in_place, gdb_mkostemp_cloexec (filename_temp.data (), O_BINARY));
-  if (out_file_fd->get () == -1)
+  /* Order matters here; we want FILE to be closed before
+     FILENAME_TEMP is unlinked, because on MS-Windows one cannot
+     delete a file that is still open.  So, we wrap the unlinker in an
+     optional and emplace it once we know the file name.  */
+  gdb::optional<gdb::unlinker> unlink_file;
+  scoped_fd out_file_fd (gdb_mkostemp_cloexec (filename_temp.data (),
+					       O_BINARY));
+  if (out_file_fd.get () == -1)
     perror_with_name (("mkstemp"));
 
-  FILE *out_file = gdb_fopen_cloexec (filename_temp.data (), "wb").release ();
+  gdb_file_up out_file = out_file_fd.to_file ("wb");
   if (out_file == nullptr)
     error (_("Can't open `%s' for writing"), filename_temp.data ());
 
-  /* Order matters here; we want FILE to be closed before FILENAME_TEMP is
-     unlinked, because on MS-Windows one cannot delete a file that is
-     still open.  (Don't call anything here that might throw until
-     file_closer is created.)  We don't need OUT_FILE_FD anymore, so we might
-     as well close it now.  */
-  out_file_fd.reset ();
-  gdb::unlinker unlink_file (filename_temp.data ());
-  gdb_file_up close_out_file (out_file);
+  unlink_file.emplace (filename_temp.data ());
 
   if (index_kind == dw_index_kind::DEBUG_NAMES)
     {
@@ -1590,45 +1588,45 @@ write_psymtabs_to_index (struct dwarf2_per_objfile *dwarf2_per_objfile,
 				+ basename + DEBUG_STR_SUFFIX);
       gdb::char_vector filename_str_temp = make_temp_filename (filename_str);
 
-      gdb::optional<scoped_fd> out_file_str_fd
-	(gdb::in_place, gdb_mkostemp_cloexec (filename_str_temp.data (),
-					      O_BINARY));
-      if (out_file_str_fd->get () == -1)
+      /* As above, arrange to unlink the file only after the file
+	 descriptor has been closed.  */
+      gdb::optional<gdb::unlinker> unlink_file_str;
+      scoped_fd out_file_str_fd
+	(gdb_mkostemp_cloexec (filename_str_temp.data (), O_BINARY));
+      if (out_file_str_fd.get () == -1)
         perror_with_name (("mkstemp"));
 
-      FILE *out_file_str
-	= gdb_fopen_cloexec (filename_str_temp.data (), "wb").release ();
+      gdb_file_up out_file_str = out_file_str_fd.to_file ("wb");
       if (out_file_str == nullptr)
 	error (_("Can't open `%s' for writing"), filename_str_temp.data ());
 
-      out_file_str_fd.reset ();
-      gdb::unlinker unlink_file_str (filename_str_temp.data ());
-      gdb_file_up close_out_file_str (out_file_str);
+      unlink_file_str.emplace (filename_str_temp.data ());
 
       const size_t total_len
-	= write_debug_names (dwarf2_per_objfile, out_file, out_file_str);
-      assert_file_size (out_file, filename_temp.data (), total_len);
+	= write_debug_names (dwarf2_per_objfile, out_file.get (),
+			     out_file_str.get ());
+      assert_file_size (out_file.get (), filename_temp.data (), total_len);
 
       /* We want to keep the file .debug_str file too.  */
-      unlink_file_str.keep ();
+      unlink_file_str->keep ();
 
       /* Close and move the str file in place.  */
-      close_out_file_str.reset ();
+      out_file_str.reset ();
       if (rename (filename_str_temp.data (), filename_str.c_str ()) != 0)
 	perror_with_name (("rename"));
     }
   else
     {
       const size_t total_len
-	= write_gdbindex (dwarf2_per_objfile, out_file);
-      assert_file_size (out_file, filename_temp.data (), total_len);
+	= write_gdbindex (dwarf2_per_objfile, out_file.get ());
+      assert_file_size (out_file.get (), filename_temp.data (), total_len);
     }
 
   /* We want to keep the file.  */
-  unlink_file.keep ();
+  unlink_file->keep ();
 
   /* Close and move the file in place.  */
-  close_out_file.reset ();
+  out_file.reset ();
   if (rename (filename_temp.data (), filename.c_str ()) != 0)
 	perror_with_name (("rename"));
 }
diff --git a/gdb/unittests/scoped_fd-selftests.c b/gdb/unittests/scoped_fd-selftests.c
index fb6a0d6..6a9c727 100644
--- a/gdb/unittests/scoped_fd-selftests.c
+++ b/gdb/unittests/scoped_fd-selftests.c
@@ -65,12 +65,29 @@ test_release ()
   SELF_CHECK (close (fd) == 0 || errno != EBADF);
 }
 
+/* Test that the file descriptor can be converted to a FILE *.  */
+static void
+test_to_file ()
+{
+  char filename[] = "scoped_fd-selftest-XXXXXX";
+
+  ::scoped_fd sfd (gdb_mkostemp_cloexec (filename));
+  SELF_CHECK (sfd.get () >= 0);
+
+  unlink (filename);
+  
+  gdb_file_up file = sfd.to_file ("rw");
+  SELF_CHECK (file != nullptr);
+  SELF_CHECK (sfd.get () == -1);
+}
+
 /* Run selftests.  */
 static void
 run_tests ()
 {
   test_destroy ();
   test_release ();
+  test_to_file ();
 }
 
 } /* namespace scoped_fd */