This allows to pass ECN bits as cmsg ancillary data with a cmsg_type of
DCCP_SCM_ECN_BITS for Data/DataAck packets.
The scope of this patch is for developing user-space applications that work
with, modify, or control the use of ECN bits on data packets.
RFC: This is an AF-independent alternative to using IP_TOS/IPV6_TCLASS for
modifying the ECN bits.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
Documentation/networking/dccp.txt | 12 ++++++++++--
include/linux/dccp.h | 1 +
net/dccp/output.c | 10 +++++++---
net/dccp/proto.c | 20 ++++++++++++++++++++
4 files changed, 38 insertions(+), 5 deletions(-)
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -32,8 +32,16 @@ is at http://www.ietf.org/html.charters/dccp-charter.html
ECN Support
===========
By default, all outgoing packets are sent with ECT(0) as per RFC 3168, sec. 5.
-This can be disabled by setting the `ecn_local' sysctl to 0 (see below). The
-ECN Nonce (RFC 3540) is not supported.
+This can be disabled by setting the `ecn_local' sysctl to 0 (see below).
+
+For Data/DataAck packets, the ECN bits can be modified by passing an appropriate
+cmsg(3) value as ancillary data to sendmsg(2). The argument is an uint8_t value
+between 0..3 (corresponding to Not-ECT, ECT(1), ECT(0), and CE). Values greater
+than 3 are not accepted. Values need to be wrapped into a cmsg(3) header:
+ cmsg->cmsg_level = SOL_DCCP;
+ cmsg->cmsg_type = DCCP_SCM_ECN_BITS;
+ cmsg->cmsg_len = CMSG_LEN(sizeof(uint8_t)); /* or CMSG_LEN(1) */
+
Missing features
================
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -202,6 +202,7 @@ enum dccp_cmsg_type {
DCCP_SCM_PRIORITY = 1,
DCCP_SCM_QPOLICY_MAX = 0xFFFF,
/* ^-- Up to here reserved exclusively for qpolicy parameters */
+ DCCP_SCM_ECN_BITS,
DCCP_SCM_MAX
};
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -53,7 +53,7 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
const u32 dccp_header_size = sizeof(*dh) +
sizeof(struct dccp_hdr_ext) +
dccp_packet_hdr_len(dcb->dccpd_type);
- int err, set_ack = 1;
+ int err, set_ack = 1, ecn_bits = INET_ECN_ECT_0;
u64 ackno = dp->dccps_gsr;
/*
* Increment GSS here already in case the option code needs it.
@@ -66,6 +66,8 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
set_ack = 0;
/* fall through */
case DCCP_PKT_DATAACK:
+ /* ECN bits of Data/DataAck are set in dccp_sendmsg() */
+ ecn_bits = DCCP_SKB_CB(skb)->dccpd_ecn;
case DCCP_PKT_RESET:
break;
@@ -130,8 +132,10 @@ static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
break;
}
- if (dp->dccps_r_ecn_ok)
- INET_ECN_xmit(sk);
+ if (dp->dccps_r_ecn_ok) {
+ inet_sk(sk)->tos &= ~INET_ECN_MASK;
+ inet_sk(sk)->tos |= ecn_bits & INET_ECN_MASK;
+ }
icsk->icsk_af_ops->send_check(sk, 0, skb);
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -707,7 +707,17 @@ EXPORT_SYMBOL_GPL(compat_dccp_getsockopt);
static int dccp_msghdr_parse(struct msghdr *msg, struct sk_buff *skb)
{
+ const struct dccp_sock *dp = dccp_sk(skb->sk);
struct cmsghdr *cmsg = CMSG_FIRSTHDR(msg);
+ u8 val;
+
+ /*
+ * Setting ECN bits via DCCP_SCM_ECN_BITS: Data/DataAck only.
+ * See dccp_transmit_skb() where further processing takes place.
+ * By default, when no cmsg bits are supplied and when ECN is not
+ * disabled, ECT(0) is used for all outgoing packets (RFC 3168, 5.).
+ */
+ DCCP_SKB_CB(skb)->dccpd_ecn = INET_ECN_ECT_0;
/*
* Assign an (opaque) qpolicy priority value to skb->priority.
@@ -739,6 +749,16 @@ static int dccp_msghdr_parse(struct msghdr *msg, struct sk_buff *skb)
return -EINVAL;
skb->priority = *(__u32 *)CMSG_DATA(cmsg);
break;
+ case DCCP_SCM_ECN_BITS:
+ if (!dp->dccps_r_ecn_ok)
+ return -EINVAL;
+ if (cmsg->cmsg_len != CMSG_LEN(sizeof(__u8)))
+ return -EINVAL;
+ val = *(__u8 *)CMSG_DATA(cmsg);
+ if (val > INET_ECN_MASK)
+ return -EINVAL;
+ DCCP_SKB_CB(skb)->dccpd_ecn = val;
+ break;
default:
return -EINVAL;
}
--
1.6.0.rc2
--
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