Merge branch 'sv/file-osync/OTP-11498'

* sv/file-osync/OTP-11498:
  Add sync option to file:open/2

Conflicts:
	erts/preloaded/ebin/prim_file.beam

3 files changed, 26 insertions, 1 deletions

diff --git a/lib/kernel/doc/src/file.xml b/lib/kernel/doc/src/file.xml
index 1118a8feee..0a4dd3ba47 100644
--- a/lib/kernel/doc/src/file.xml
+++ b/lib/kernel/doc/src/file.xml
@@ -826,6 +826,16 @@
           <item>
             <p><c>File</c> must be <c>iodata()</c>. Returns an <c>fd()</c> which lets the <c>file</c> module operate on the data in-memory as if it is a file.</p>
           </item>
+          <tag><c>sync</c></tag>
+          <item>
+            <p>On platforms that support it, enables the POSIX <c>O_SYNC</c> synchronous I/O flag or its platform-dependent
+            equivalent (e.g., <c>FILE_FLAG_WRITE_THROUGH</c> on Windows) so that writes to the file block until the data has
+            been physically written to disk. Be aware, though, that the exact semantics of this flag differ from platform to
+            platform; for example, neither Linux nor Windows guarantees that all file metadata are also written before the call
+            returns. For precise semantics, check the details of your platform's documentation. On platforms with no
+            support for POSIX <c>O_SYNC</c> or equivalent, use of the <c>sync</c> flag causes <c>open</c> to return
+            <c>{error, enotsup}</c>.</p>
+          </item>
         </taglist>
         <p>Returns:</p>
         <taglist>
diff --git a/lib/kernel/src/file.erl b/lib/kernel/src/file.erl
index 5c0f3b7ceb..b5152018e0 100644
--- a/lib/kernel/src/file.erl
+++ b/lib/kernel/src/file.erl
@@ -95,7 +95,8 @@
                       Delay :: non_neg_integer()}
 		   | 'delayed_write' | {'read_ahead', Size :: pos_integer()}
 		   | 'read_ahead' | 'compressed'
-		   | {'encoding', unicode:encoding()}.
+		   | {'encoding', unicode:encoding()}
+		   | sync.
 -type deep_list() :: [char() | atom() | deep_list()].
 -type name()      :: string() | atom() | deep_list().
 -type name_all()  :: string() | atom() | deep_list() | (RawFilename :: binary()).
diff --git a/lib/kernel/test/file_SUITE.erl b/lib/kernel/test/file_SUITE.erl
index e4c8f0ffaf..c75639ae7e 100644
--- a/lib/kernel/test/file_SUITE.erl
+++ b/lib/kernel/test/file_SUITE.erl
@@ -805,6 +805,20 @@ new_modes(Config) when is_list(Config) ->
     ?line {ok, [$\[]} = ?FILE_MODULE:read(Fd6, 1),
     ?line ok = ?FILE_MODULE:close(Fd6),
 
+    %% write and sync
+    case ?FILE_MODULE:open(Name1, [write, sync]) of
+	{ok, Fd7} ->
+	    ok = io:write(Fd7, Marker),
+	    ok = io:put_chars(Fd7, ".\n"),
+	    ok = ?FILE_MODULE:close(Fd7),
+	    {ok, Fd8} = ?FILE_MODULE:open(Name1, [read]),
+	    {ok, Marker} = io:read(Fd8, prompt),
+	    ok = ?FILE_MODULE:close(Fd8);
+	{error, enotsup} ->
+	    %% for platforms that don't support the sync option
+	    ok
+    end,
+
     ?line [] = flush(),
     ?line test_server:timetrap_cancel(Dog),
     ok.