erts/kernel: sendfile no longer uses async threads

This has been done because a slow client attack is possible if the
async thread pool is used. The scenario is:

Client does a request for a file and then slowly receives the file one
byte at a time. This will eventually fill the async thread pool with blocking
sendfile operations and thus starving the vm of all file operations.

If you still want to use the async threads pool for sendfile an option to
enable it has been introduced.

1 files changed, 7 insertions, 8 deletions

diff --git a/lib/kernel/src/file.erl b/lib/kernel/src/file.erl
index b5152018e0..23cf74f80f 100644
--- a/lib/kernel/src/file.erl
+++ b/lib/kernel/src/file.erl
@@ -111,7 +111,8 @@
 -type date_time() :: calendar:datetime().
 -type posix_file_advise() :: 'normal' | 'sequential' | 'random'
                            | 'no_reuse' | 'will_need' | 'dont_need'.
--type sendfile_option() :: {chunk_size, non_neg_integer()}.
+-type sendfile_option() :: {chunk_size, non_neg_integer()}
+			 | {use_threads, boolean()}.
 -type file_info_option() :: {'time', 'local'} | {'time', 'universal'} 
 			  | {'time', 'posix'}.
 %%% BIFs
@@ -1229,8 +1230,7 @@ change_time(Name, {{AY, AM, AD}, {AH, AMin, ASec}}=Atime,
 sendfile(File, _Sock, _Offet, _Bytes, _Opts) when is_pid(File) ->
     {error, badarg};
 sendfile(File, Sock, Offset, Bytes, []) ->
-    sendfile(File, Sock, Offset, Bytes, ?MAX_CHUNK_SIZE, [], [],
-	     false, false, false);
+    sendfile(File, Sock, Offset, Bytes, ?MAX_CHUNK_SIZE, [], [], []);
 sendfile(File, Sock, Offset, Bytes, Opts) ->
     ChunkSize0 = proplists:get_value(chunk_size, Opts, ?MAX_CHUNK_SIZE),
     ChunkSize = if ChunkSize0 > ?MAX_CHUNK_SIZE ->
@@ -1240,8 +1240,7 @@ sendfile(File, Sock, Offset, Bytes, Opts) ->
     %% Support for headers, trailers and options has been removed because the
     %% Darwin and BSD API for using it does not play nice with
     %% non-blocking sockets. See unix_efile.c for more info.
-    sendfile(File, Sock, Offset, Bytes, ChunkSize, [], [],
-	     false,false,false).
+    sendfile(File, Sock, Offset, Bytes, ChunkSize, [], [], Opts).
 
 %% sendfile/2
 -spec sendfile(Filename, Socket) ->
@@ -1261,17 +1260,17 @@ sendfile(Filename, Sock)  ->
 
 %% Internal sendfile functions
 sendfile(#file_descriptor{ module = Mod } = Fd, Sock, Offset, Bytes,
-	 ChunkSize, Headers, Trailers, Nodiskio, MNowait, Sync)
+	 ChunkSize, Headers, Trailers, Opts)
   when is_port(Sock) ->
     case Mod:sendfile(Fd, Sock, Offset, Bytes, ChunkSize, Headers, Trailers,
-		      Nodiskio, MNowait, Sync) of
+		      Opts) of
 	{error, enotsup} ->
 	    sendfile_fallback(Fd, Sock, Offset, Bytes, ChunkSize,
 			      Headers, Trailers);
 	Else ->
 	    Else
     end;
-sendfile(_,_,_,_,_,_,_,_,_,_) ->
+sendfile(_,_,_,_,_,_,_,_) ->
     {error, badarg}.
 
 %%%