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File 2602-erts-Limit-the-automatic-max-buffer-for-UDP-to-2-16.patch of Package erlang (Revision 66a224e208ffe9ee89602bad56a74dfa)

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From a9d361b4be7d6329bedd7b37d454c1abf4f27233 Mon Sep 17 00:00:00 2001
From: Lukas Larsson <lukas@erlang.org>
Date: Thu, 21 Jun 2018 11:00:25 +0200
Subject: [PATCH 2/2] erts: Limit the automatic max buffer for UDP to 2^16

There is no reason to have a larger buffer than this as
the recvmsg call will never return more data.

OTP-15206
---
 erts/emulator/drivers/common/inet_drv.c |  9 ++++++++-
 lib/kernel/doc/src/inet.xml             | 19 ++++++++++---------
 lib/kernel/test/gen_udp_SUITE.erl       | 12 ++++++++++--
 3 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/erts/emulator/drivers/common/inet_drv.c b/erts/emulator/drivers/common/inet_drv.c
index 833befefd1..2048d0f625 100644
--- a/erts/emulator/drivers/common/inet_drv.c
+++ b/erts/emulator/drivers/common/inet_drv.c
@@ -1549,6 +1549,8 @@ static void *realloc_wrapper(void *current, ErlDrvSizeT size){
 # define LOAD_ASSOC_ID LOAD_UINT
 # define LOAD_ASSOC_ID_CNT LOAD_UINT_CNT
 # define SCTP_ANC_BUFF_SIZE INET_DEF_BUFFER/2 /* XXX: not very good... */
+#else
+# define IS_SCTP(desc) 0
 #endif
 
 #ifdef HAVE_UDP
@@ -6436,7 +6438,12 @@ static int inet_set_opts(inet_descriptor* desc, char* ptr, int len)
 		(long)desc->port, desc->s, res));
 	if (type == SO_RCVBUF) {
 	 /* make sure we have desc->bufsz >= SO_RCVBUF */
-	 if (ival > desc->bufsz)
+ if (ival > (1 << 16) && desc->stype == SOCK_DGRAM && !IS_SCTP(desc))
+ /* For UDP we don't want to automatically
+ set the buffer size to be larger than
+ the theoretical max MTU */
+ desc->bufsz = 1 << 16;
+	 else if (ival > desc->bufsz)
 		desc->bufsz = ival;
 	}
 }
diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index e6a7962c5a..f281d61459 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -734,22 +734,23 @@ get_tcpi_sacked(Sock) ->
 </item>
 <tag><c>{buffer, Size}</c></tag>
 <item>
- The size of the user-level software buffer used by
- the driver. 
- Not to be confused with options <c>sndbuf</c>
+ The size of the user-level buffer used by
+ the driver. Not to be confused with options <c>sndbuf</c>
 and <c>recbuf</c>, which correspond to the
- Kernel socket buffers. It is recommended
- to have <c>val(buffer) &gt;= max(val(sndbuf),val(recbuf))</c> to
+ Kernel socket buffers. For TCP it is recommended
+ to have <c>val(buffer) &gt;= val(recbuf)</c> to
 avoid performance issues because of unnecessary copying.
+ For UDP the same recommendation applies, but the max should
+ not be larger than the MTU of the network path.
 <c>val(buffer)</c> is automatically set to the above
- maximum when values <c>sndbuf</c> or <c>recbuf</c> are set.
- However, as the sizes set for <c>sndbuf</c> and <c>recbuf</c>
+ maximum when <c>recbuf</c> is set.
+ However, as the size set for <c>recbuf</c>
 usually become larger, you are encouraged to use
 <seealso marker="#getopts/2"><c>getopts/2</c></seealso>
 to analyze the behavior of your operating system.
 Note that this is also the maximum amount of data that can be
-	 received from a single recv call. If you are using higher than 
-	 normal MTU consider setting buffer higher. 
+	 received from a single recv call. If you are using higher than
+	 normal MTU consider setting buffer higher.
 </item>
 <tag><c>{delay_send, Boolean}</c></tag>
 <item>
diff --git a/lib/kernel/test/gen_udp_SUITE.erl b/lib/kernel/test/gen_udp_SUITE.erl
index b39399b18a..3acfff929e 100644
--- a/lib/kernel/test/gen_udp_SUITE.erl
+++ b/lib/kernel/test/gen_udp_SUITE.erl
@@ -34,7 +34,7 @@
 -export([init_per_testcase/2, end_per_testcase/2]).
 
 -export([send_to_closed/1, active_n/1,
-	 buffer_size/1, binary_passive_recv/1, bad_address/1,
+	 buffer_size/1, binary_passive_recv/1, max_buffer_size/1, bad_address/1,
 	 read_packets/1, recv_poll_after_active_once/1,
 open_fd/1, connect/1, implicit_inet6/1,
 	 local_basic/1, local_unbound/1,
@@ -50,6 +50,7 @@ suite() ->
 send_to_closed,
 buffer_size,
 binary_passive_recv,
+ max_buffer_size,
 bad_address,
 read_packets,
 recv_poll_after_active_once,
@@ -260,6 +261,14 @@ buffer_size_server_recv(Socket, IP, Port, Cnt) ->
 end.
 
 
+%%-------------------------------------------------------------
+%% OTP-15206: Keep buffer small for udp
+%%-------------------------------------------------------------
+max_buffer_size(Config) when is_list(Config) ->
+ {ok, Socket} = gen_udp:open(0, [binary]),
+ ok = inet:setopts(Socket,[{recbuf, 1 bsl 20}]),
+ {ok, [{buffer, 65536}]} = inet:getopts(Socket,[buffer]),
+ gen_udp:close(Socket).
 
 %%-------------------------------------------------------------
 %% OTP-3823 gen_udp:recv does not return address in binary mode
-- 
2.16.4

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File 2602-erts-Limit-the-automatic-max-buffer-for-UDP-to-2-16.patch of Package erlang (Revision 66a224e208ffe9ee89602bad56a74dfa)

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