[DCCP] [RFC]: Reworked queueing policy patch set
This is a re-worked version of Tomasz's priority-queueing patch set for
DCCP. The essential internals of his patch set have been left untouched,
in particular the prio/simple algorithms are the same as before.
The changes for which I am asking for comments are:
1. Fewer files:
---------------
The patch set originally introduced 4 new files:
50 net/dccp/qpolicy.c
48 net/dccp/qpolicy.h
70 net/dccp/qpolicy_prio.c
36 net/dccp/qpolicy_simple.c
Given that each file has less than 100 lines, it seemed better to put them
all into one file and export the declarations in dccp.h, the result is now:
143 net/dccp/qpolicy.c
With less than 150 lines, there is still room for a few more policies.
2. Let pop() return result
--------------------------
* at least for the forseeable future, the underlying queue is sk_write_queue;
* an skb can not be on two lists at the same time;
* thus skb_unlink will always be part of implementing pop();
* having pop() return the skb is more versatile (compare Assembler pop()).
3. Hide internals of implementation
-----------------------------------
There had been discussion on hiding the internals, the present approach
* uses symbolic identifiers (enum) to refer to policies;
* makes the function table local to qpolicy.c, so that
* dccp_sock only needs to take the policy identifier;
* makes tx_qlen a socket member of dccp_sock (there was a bug in the
implementation -- tx_qlen was shared by all sockets using the same policy);
* default policy as well as inheriting policy to child socket now implicit:
- default policy (ID=0) set due to zeroing socket on allocation,
- inheriting policy due to performing sock_copy() on the policy ID;
4. Clerical changes
-------------------
Some work done here, such as adding documentation, aligning identifiers etc.
If people (Tomasz in particular) are ok with the changes, I would like to add
this to the test tree, otherwise will keep it separate as subtree "qpolicy" in
git://eden-feed.erg.abdn.ac.uk/dccp_exp
during discussions.
Gerrit
---
Documentation/networking/dccp.txt | 11 ++
include/linux/dccp.h | 20 +++++
net/dccp/Makefile | 2
net/dccp/dccp.h | 45 +++++++----
net/dccp/output.c | 6 -
net/dccp/proto.c | 26 ++++++
net/dccp/qpolicy.c | 143 ++++++++++++++++++++++++++++++++++++++
7 files changed, 231 insertions(+), 22 deletions(-)
--- /dev/null
+++ b/net/dccp/qpolicy.c
@@ -0,0 +1,143 @@
+/*
+ * net/dccp/qpolicy.c
+ *
+ * An implementation of the DCCP protocol
+ *
+ * Copyright (c) 2008 Tomasz Grobelny <tomasz@xxxxxxxxxxxxxxxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License v2
+ * as published by the Free Software Foundation.
+ */
+#include "dccp.h"
+
+/*
+ * Simple Dequeueing Policy
+ */
+static void simple_push(struct sock *sk, struct sk_buff *skb,
+ const struct dccp_packet_info *dcp)
+{
+ skb_queue_tail(&sk->sk_write_queue, skb);
+}
+
+static int simple_full(struct sock *sk)
+{
+ return dccp_sk(sk)->dccps_tx_qlen &&
+ sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
+}
+
+static struct sk_buff *simple_top(struct sock *sk)
+{
+ return skb_peek(&sk->sk_write_queue);
+}
+
+/*
+ * Priority-based Dequeueing Policy
+ */
+static struct sk_buff *prio_get_worst_skb(struct sock *sk)
+{
+ struct sk_buff *skb, *worst = NULL;
+ int worstp = -128;
+
+ skb_queue_walk(&sk->sk_write_queue, skb)
+ if (DCCP_SKB_CB(skb)->dccpd_policy.priority >= worstp) {
+ worstp = DCCP_SKB_CB(skb)->dccpd_policy.priority;
+ worst = skb;
+ }
+ return worst;
+}
+
+static void prio_push(struct sock *sk, struct sk_buff *skb,
+ const struct dccp_packet_info *dcp)
+{
+ struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
+
+ dcb->dccpd_policy.priority = 127;
+ if (dcp)
+ memcpy(&dcb->dccpd_policy, dcp, sizeof(*dcp));
+
+ skb_queue_tail(&sk->sk_write_queue, skb);
+
+ if (sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen) {
+ struct sk_buff *worst = prio_get_worst_skb(sk);
+
+ skb_unlink(worst, &sk->sk_write_queue);
+ kfree_skb(worst);
+ }
+}
+
+/** we can always push a packet into the queue => queue is never full */
+static int prio_full(struct sock *sk)
+{
+ return 0;
+}
+
+static struct sk_buff *prio_get_best_skb(struct sock *sk)
+{
+ struct sk_buff *skb, *best = NULL;
+ int bestp = 127;
+
+ skb_queue_walk(&sk->sk_write_queue, skb)
+ if (DCCP_SKB_CB(skb)->dccpd_policy.priority <= bestp) {
+ bestp = DCCP_SKB_CB(skb)->dccpd_policy.priority;
+ best = skb;
+ }
+ return best;
+}
+
+/**
+ * struct dccp_qpolicy_operations - TX Packet Dequeueing Interface
+ * @push: add a new @skb with possibly a struct dccp_packet_info
+ * @full: indicates that no more packets will be admitted
+ * @top: peeks at whatever the queueing policy defines as top
+ */
+static struct dccp_qpolicy_operations {
+ void (*push) (struct sock *sk, struct sk_buff *skb,
+ const struct dccp_packet_info *dcp);
+ int (*full) (struct sock *sk);
+ struct sk_buff* (*top) (struct sock *sk);
+
+} qpol_table[DCCPQ_POLICY_MAX] = {
+ [DCCPQ_POLICY_SIMPLE] = {
+ .push = simple_push,
+ .full = simple_full,
+ .top = simple_top,
+ },
+ [DCCPQ_POLICY_PRIO] = {
+ .push = prio_push,
+ .full = prio_full,
+ .top = prio_get_best_skb,
+ },
+};
+
+/*
+ * Wrappers for methods provided by policy currently in use
+ */
+void qpolicy_push(struct sock *sk, struct sk_buff *skb, struct msghdr *msg)
+{
+ struct dccp_packet_info *dcp = NULL;
+
+ if (msg->msg_control != NULL && msg->msg_controllen == sizeof(*dcp))
+ dcp = (struct dccp_packet_info *)msg->msg_control;
+
+ qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb, dcp);
+}
+
+int qpolicy_full(struct sock *sk)
+{
+ return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
+}
+
+struct sk_buff *qpolicy_top(struct sock *sk)
+{
+ return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
+}
+
+struct sk_buff *qpolicy_pop(struct sock *sk)
+{
+ struct sk_buff *skb = qpolicy_top(sk);
+
+ if (skb)
+ skb_unlink(skb, &sk->sk_write_queue);
+ return skb;
+}
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -195,6 +195,20 @@ enum dccp_feature_numbers {
DCCPF_MAX_CCID_SPECIFIC = 255,
};
+/* DCCP TX Dequeueing Policy */
+enum dccp_packet_dequeueing_policy {
+ DCCPQ_POLICY_SIMPLE,
+ DCCPQ_POLICY_PRIO,
+ DCCPQ_POLICY_MAX
+};
+/**
+ * struct dccp_packet_info - Per-packet TX dequeueing information
+ * @priority: packet priority, lower value => packet more likely to be sent
+ */
+struct dccp_packet_info {
+ __s8 priority;
+};
+
/* DCCP socket options */
#define DCCP_SOCKOPT_PACKET_SIZE 1 /* XXX deprecated, without effect */
#define DCCP_SOCKOPT_SERVICE 2
@@ -208,6 +222,8 @@ enum dccp_feature_numbers {
#define DCCP_SOCKOPT_CCID 13
#define DCCP_SOCKOPT_TX_CCID 14
#define DCCP_SOCKOPT_RX_CCID 15
+#define DCCP_SOCKOPT_QPOLICY_ID 16
+#define DCCP_SOCKOPT_QPOLICY_TXQLEN 17
#define DCCP_SOCKOPT_CCID_RX_INFO 128
#define DCCP_SOCKOPT_CCID_TX_INFO 192
@@ -459,6 +475,8 @@ struct dccp_ackvec;
* @dccps_hc_rx_ccid - CCID used for the receiver (or receiving half-connection)
* @dccps_hc_tx_ccid - CCID used for the sender (or sending half-connection)
* @dccps_options_received - parsed set of retrieved options
+ * @dccps_qpolicy - TX dequeueing policy, one of %dccp_packet_dequeueing_policy
+ * @dccps_tx_qlen - maximum length of the TX queue
* @dccps_role - role of this sock, one of %dccp_role
* @dccps_hc_rx_insert_options - receiver wants to add options when acking
* @dccps_hc_tx_insert_options - sender wants to add options when sending
@@ -501,6 +519,8 @@ struct dccp_sock {
struct ccid *dccps_hc_rx_ccid;
struct ccid *dccps_hc_tx_ccid;
struct dccp_options_received dccps_options_received;
+ __u8 dccps_qpolicy;
+ __u32 dccps_tx_qlen;
enum dccp_role dccps_role:2;
__u8 dccps_hc_rx_insert_options:1;
__u8 dccps_hc_tx_insert_options:1;
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -187,6 +187,7 @@ int dccp_init_sock(struct sock *sk, cons
dp->dccps_rate_last = jiffies;
dp->dccps_role = DCCP_ROLE_UNDEFINED;
dp->dccps_service = DCCP_SERVICE_CODE_IS_ABSENT;
+ dp->dccps_tx_qlen = sysctl_dccp_tx_qlen;
INIT_LIST_HEAD(&dp->dccps_featneg);
/* control socket doesn't need feat nego */
@@ -540,6 +541,20 @@ static int do_dccp_setsockopt(struct soc
case DCCP_SOCKOPT_RECV_CSCOV:
err = dccp_setsockopt_cscov(sk, val, true);
break;
+ case DCCP_SOCKOPT_QPOLICY_ID:
+ if (sk->sk_state != DCCP_CLOSED)
+ err = -EISCONN;
+ else if (val < 0 || val >= DCCPQ_POLICY_MAX)
+ err = -EINVAL;
+ else
+ dp->dccps_qpolicy = val;
+ break;
+ case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+ if (val < 0)
+ err = -EINVAL;
+ else
+ dp->dccps_tx_qlen = val;
+ break;
default:
err = -ENOPROTOOPT;
break;
@@ -643,6 +658,12 @@ static int do_dccp_getsockopt(struct soc
case DCCP_SOCKOPT_RECV_CSCOV:
val = dp->dccps_pcrlen;
break;
+ case DCCP_SOCKOPT_QPOLICY_ID:
+ val = dp->dccps_qpolicy;
+ break;
+ case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+ val = dp->dccps_tx_qlen;
+ break;
case 128 ... 191:
return ccid_hc_rx_getsockopt(dp->dccps_hc_rx_ccid, sk, optname,
len, (u32 __user *)optval, optlen);
@@ -700,8 +721,7 @@ int dccp_sendmsg(struct kiocb *iocb, str
lock_sock(sk);
- if (sysctl_dccp_tx_qlen &&
- (sk->sk_write_queue.qlen >= sysctl_dccp_tx_qlen)) {
+ if (qpolicy_full(sk)) {
rc = -EAGAIN;
goto out_release;
}
@@ -729,7 +749,7 @@ int dccp_sendmsg(struct kiocb *iocb, str
if (rc != 0)
goto out_discard;
- skb_queue_tail(&sk->sk_write_queue, skb);
+ qpolicy_push(sk, skb, msg);
dccp_write_xmit(sk);
out_release:
release_sock(sk);
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -215,6 +215,18 @@ extern void dccp_reqsk_send_ack(struct s
extern void dccp_send_sync(struct sock *sk, const u64 seq,
const enum dccp_pkt_type pkt_type);
+/*
+ * TX Packet Dequeueing Interface
+ */
+extern void qpolicy_push(struct sock *sk, struct sk_buff *skb,
+ struct msghdr *msg);
+extern int qpolicy_full(struct sock *sk);
+extern struct sk_buff *qpolicy_top(struct sock *sk);
+extern struct sk_buff *qpolicy_pop(struct sock *sk);
+
+/*
+ * TX Packet Output and TX Timers
+ */
extern void dccp_write_xmit(struct sock *sk);
extern void dccp_write_space(struct sock *sk);
extern void dccp_flush_write_queue(struct sock *sk, long *time_budget);
@@ -313,14 +325,16 @@ static inline int dccp_bad_service_code(
/**
* dccp_skb_cb - DCCP per-packet control information
- * @dccpd_type: one of %dccp_pkt_type (or unknown)
- * @dccpd_ccval: CCVal field (5.1), see e.g. RFC 4342, 8.1
- * @dccpd_reset_code: one of %dccp_reset_codes
- * @dccpd_reset_data: Data1..3 fields (depend on @dccpd_reset_code)
- * @dccpd_opt_len: total length of all options (5.8) in the packet
- * @dccpd_seq: sequence number
- * @dccpd_ack_seq: acknowledgment number subheader field value
- * This is used for transmission as well as for reception.
+ * @header: IPv4/6 parameters
+ * @dccpd_type: one of %dccp_pkt_type (or unknown)
+ * @dccpd_ccval: CCVal field (5.1), see e.g. RFC 4342, 8.1
+ * @dccpd_reset_code: one of %dccp_reset_codes
+ * @dccpd_reset_data: Data1..3 fields (depend on @dccpd_reset_code)
+ * @dccpd_opt_len: total length of all options (5.8) in the packet
+ * @dccpd_seq: sequence number
+ * @dccpd_ack_seq: acknowledgment number subheader field value
+ * @dccpd_policy: packet dequeueing policy (TX packets only)
+ * This struct is used for transmission as well as for reception.
*/
struct dccp_skb_cb {
union {
@@ -329,13 +343,14 @@ struct dccp_skb_cb {
struct inet6_skb_parm h6;
#endif
} header;
- __u8 dccpd_type:4;
- __u8 dccpd_ccval:4;
- __u8 dccpd_reset_code,
- dccpd_reset_data[3];
- __u16 dccpd_opt_len;
- __u64 dccpd_seq;
- __u64 dccpd_ack_seq;
+ __u8 dccpd_type:4;
+ __u8 dccpd_ccval:4;
+ __u8 dccpd_reset_code,
+ dccpd_reset_data[3];
+ __u16 dccpd_opt_len;
+ __u64 dccpd_seq;
+ __u64 dccpd_ack_seq;
+ struct dccp_packet_info dccpd_policy;
};
#define DCCP_SKB_CB(__skb) ((struct dccp_skb_cb *)&((__skb)->cb[0]))
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -45,6 +45,17 @@ http://linux-net.osdl.org/index.php/DCCP
Socket options
==============
+DCCP_SOCKOPT_QPOLICY_ID sets the dequeueing policy for outgoing packets. It
+takes an integer number as argument and can only be set before establishing
+a connection (i.e. changes during an established connection are not supported).
+Currently defined IDs are "simple" (DCCPQ_POLICY_SIMPLE) and a priority-based
+variant (DCCPQ_POLICY_PRIO). In the latter case, a struct dccp_packet_info can
+be passed as ancillary data in the msg_control field of sendmsg(2).
+
+DCCP_SOCKOPT_QPOLICY_TXQLEN sets the maximum TX queue length. This is relevant only for
+those TX dequeueing policies that honour this upper bound (currently only the
+simple/default policy does this). This socket option overrides the default value
+of the sysctl /proc/sys/net/dccp/default/tx_qlen.
DCCP_SOCKOPT_SERVICE sets the service. The specification mandates use of
service codes (RFC 4340, sec. 8.1.2); if this socket option is not set,
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -238,7 +238,7 @@ static void dccp_xmit_packet(struct sock
{
int err, len;
struct dccp_sock *dp = dccp_sk(sk);
- struct sk_buff *skb = skb_dequeue(&sk->sk_write_queue);
+ struct sk_buff *skb = qpolicy_pop(sk);
if (unlikely(skb == NULL))
return;
@@ -328,7 +328,7 @@ void dccp_write_xmit(struct sock *sk)
struct dccp_sock *dp = dccp_sk(sk);
struct sk_buff *skb;
- while ((skb = skb_peek(&sk->sk_write_queue))) {
+ while ((skb = qpolicy_top(sk))) {
int rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
switch (ccid_packet_dequeue_eval(rc)) {
@@ -342,7 +342,7 @@ void dccp_write_xmit(struct sock *sk)
dccp_xmit_packet(sk);
break;
case CCID_PACKET_ERR:
- skb_dequeue(&sk->sk_write_queue);
+ qpolicy_pop(sk);
kfree_skb(skb);
dccp_pr_debug("packet discarded due to err=%d\n", rc);
}
--- a/net/dccp/Makefile
+++ b/net/dccp/Makefile
@@ -1,7 +1,7 @@
obj-$(CONFIG_IP_DCCP) += dccp.o dccp_ipv4.o
dccp-y := ccid.o feat.o input.o minisocks.o options.o \
- output.o proto.o timer.o ackvec.o
+ output.o proto.o timer.o ackvec.o qpolicy.o
dccp_ipv4-y := ipv4.o
The University of Aberdeen is a charity registered in Scotland, No SC013683.
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