Implement file:sendfile

Allow Erlang code to use sendfile() where available by wrapping it as
file:sendfile/4 and file:sendfile/2.

sendfile(2) - Linux man page:
"sendfile() copies data between one file descriptor and another.
Because this copying is done within the kernel, sendfile() is more
efficient than the combination of read(2) and write(2), which would
require transferring data to and from user space."

2 files changed, 65 insertions, 1 deletions

diff --git a/lib/kernel/src/file.erl b/lib/kernel/src/file.erl
index 706c60caaf..fba9a86e95 100644
--- a/lib/kernel/src/file.erl
+++ b/lib/kernel/src/file.erl
@@ -41,7 +41,7 @@
 	 pread/2, pread/3, pwrite/2, pwrite/3,
 	 read_line/1,
 	 position/2, truncate/1, datasync/1, sync/1,
-	 copy/2, copy/3]).
+	 copy/2, copy/3, sendfile/4, sendfile/2]).
 %% High level operations
 -export([consult/1, path_consult/2]).
 -export([eval/1, eval/2, path_eval/2, path_eval/3, path_open/3]).
@@ -335,6 +335,62 @@ raw_write_file_info(Name, #file_info{} = Info) ->
 	    Error
     end.
 
+%% sendfile/5
+%% TODO: add more guards? export sendfile/5?
+-spec sendfile(File, Sock, Offset, Bytes, ChunkSize)
+	      -> {'ok', non_neg_integer()} | {'error', posix()} when
+      File::io_device(), Sock::port() | integer(),
+      Offset::non_neg_integer(), Bytes::non_neg_integer(),
+      ChunkSize::non_neg_integer().
+sendfile(File, Sock, Offset, Bytes, ChunkSize) when is_integer(Sock)
+						    andalso is_pid(File) ->
+    R = file_request(File, {sendfile, Sock, Offset, Bytes, ChunkSize}),
+    wait_file_reply(File, R);
+sendfile(File, Sock, Offset, Bytes, ChunkSize) when is_port(Sock)
+						    andalso is_pid(File) ->
+    {ok, SockFD} = prim_inet:getfd(Sock),
+    sendfile(File, SockFD, Offset, Bytes, ChunkSize);
+sendfile(#file_descriptor{module = Module} = Handle, Sock,
+	 Offset, Bytes, ChunkSize) when is_integer(Sock) ->
+    Module:sendfile(Handle, Sock, Offset, Bytes, ChunkSize);
+sendfile(#file_descriptor{module = _Module} = Handle, Sock,
+	 Offset, Bytes, ChunkSize) when is_port(Sock) ->
+    {ok, SockFD} = prim_inet:getfd(Sock),
+    sendfile(Handle, SockFD, Offset, Bytes, ChunkSize);
+sendfile(_, _, _, _, _) ->
+    {error, badarg}.
+
+-define(SENDFILE_CHUNK_LIMIT, 2147483648).	% 2GB
+
+%% Limit chunksize to work around 4 byte off_t/size_t limits
+sendfile_chunksize(Bytes, Limit) ->
+    case Bytes >= Limit of
+	true -> Limit - 1;
+	false -> Bytes
+    end.
+
+-spec sendfile(File, Sock, Offset, Bytes)
+	      -> {'ok', non_neg_integer()} | {'error', posix()} when
+      File::io_device(), Sock::port() | integer(),
+      Offset::non_neg_integer(), Bytes::non_neg_integer().
+sendfile(File, Sock, Offset, Bytes) ->
+    ChunkSize = sendfile_chunksize(Bytes, ?SENDFILE_CHUNK_LIMIT),
+    sendfile(File, Sock, Offset, Bytes, ChunkSize).
+
+%% sendfile/2
+%% TODO: add guards?
+-spec sendfile(File, Sock) -> {'ok', non_neg_integer()} | {'error', posix()}
+				  when File::name(), Sock::port().
+sendfile(File, Sock) ->
+    Offset = 0,
+    {ok, #file_info{size = Bytes}} = read_file_info(File),
+    %% TODO: use file:open/2 and file:read_file_info/1 instead of local calls?
+    {ok, Fd} = open(File, [read, raw, binary]),
+    ChunkSize = sendfile_chunksize(Bytes, ?SENDFILE_CHUNK_LIMIT),
+    Res = sendfile(Fd, Sock, Offset, Bytes, ChunkSize),
+    ok = close(Fd),
+    Res.
+
 %%%-----------------------------------------------------------------
 %%% File io server functions.
 %%% They operate on a single open file.
diff --git a/lib/kernel/src/file_io_server.erl b/lib/kernel/src/file_io_server.erl
index 14da9c1a55..78d3d24394 100644
--- a/lib/kernel/src/file_io_server.erl
+++ b/lib/kernel/src/file_io_server.erl
@@ -249,6 +249,14 @@ file_request(close,
 file_request({position,At}, 
 	     #state{handle=Handle,buf=Buf}=State) ->
     std_reply(position(Handle, At, Buf), State);
+file_request({sendfile,DestFD,Offset,Bytes,ChunkSize},
+	     #state{handle=Handle}=State) ->
+    case ?PRIM_FILE:sendfile(Handle, DestFD, Offset, Bytes, ChunkSize) of
+	{error,_}=Reply ->
+	    {stop,normal,Reply,State};
+	Reply ->
+	    {reply,Reply,State}
+    end;
 file_request(truncate, 
 	     #state{handle=Handle}=State) ->
     case ?PRIM_FILE:truncate(Handle) of