Commit fade756f authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp: Set per-connection CCIDs via socket options 



With this patch, TX/RX CCIDs can now be changed on a per-connection basis, which
overrides the defaults set by the global sysctl variables for TX/RX CCIDs.

To make full use of this facility, the remaining patches of this patch set are
needed, which track dependencies and activate negotiated feature values.

Note on the maximum number of CCIDs that can be registered:
-----------------------------------------------------------
The maximum number of CCIDs that can be registered on the socket is constrained
by the space in a Confirm/Change feature negotiation option. 

The space in these in turn depends on the size of header options as defined
in RFC 4340, 5.8. Since this is a recurring constant, it has been moved from
ackvec.h into linux/dccp.h, clarifying its purpose.

Relative to this size, the maximum number of CCID identifiers that can be 
present in a Confirm option (which always consumes 1 byte more than a Change
option, cf. 6.1) is 2 bytes less than the maximum TLV size: one for the
CCID-feature-type and one for the selected value.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 73bbe095

Documentation/networking/dccp.txt

+14 −0
Original line number Diff line number Diff line
@@ -61,6 +61,20 @@ DCCP_SOCKOPT_AVAILABLE_CCIDS is also read-only and returns the list of CCIDs 
supported by the endpoint (see include/linux/dccp.h for symbolic constants).

The caller needs to provide a sufficiently large (> 2) array of type uint8_t.



DCCP_SOCKOPT_CCID is write-only and sets both the TX and RX CCIDs at the same

time, combining the operation of the next two socket options. This option is

preferrable over the latter two, since often applications will use the same

type of CCID for both directions; and mixed use of CCIDs is not currently well

understood. This socket option takes as argument at least one uint8_t value, or

an array of uint8_t values, which must match available CCIDS (see above). CCIDs

must be registered on the socket before calling connect() or listen().



DCCP_SOCKOPT_TX_CCID is read/write. It returns the current CCID (if set) or sets

the preference list for the TX CCID, using the same format as DCCP_SOCKOPT_CCID.

Please note that the getsockopt argument type here is `int', not uint8_t.



DCCP_SOCKOPT_RX_CCID is analogous to DCCP_SOCKOPT_TX_CCID, but for the RX CCID.



DCCP_SOCKOPT_SERVER_TIMEWAIT enables the server (listening socket) to hold

timewait state when closing the connection (RFC 4340, 8.3). The usual case is

that the closing server sends a CloseReq, whereupon the client holds timewait

include/linux/dccp.h

+5 −0
Original line number Diff line number Diff line
@@ -168,6 +168,8 @@ enum { 
	DCCPO_MIN_CCID_SPECIFIC = 128,

	DCCPO_MAX_CCID_SPECIFIC = 255,

};

/* maximum size of a single TLV-encoded DCCP option (sans type/len bytes) */

#define DCCP_SINGLE_OPT_MAXLEN	253



/* DCCP CCIDS */

enum {
@@ -203,6 +205,9 @@ enum dccp_feature_numbers { 
#define DCCP_SOCKOPT_SEND_CSCOV		10

#define DCCP_SOCKOPT_RECV_CSCOV		11

#define DCCP_SOCKOPT_AVAILABLE_CCIDS	12

#define DCCP_SOCKOPT_CCID		13

#define DCCP_SOCKOPT_TX_CCID		14

#define DCCP_SOCKOPT_RX_CCID		15

#define DCCP_SOCKOPT_CCID_RX_INFO	128

#define DCCP_SOCKOPT_CCID_TX_INFO	192

net/dccp/ackvec.c

+4 −5
Original line number Diff line number Diff line
@@ -12,7 +12,6 @@ 
#include "ackvec.h"

#include "dccp.h"



#include <linux/dccp.h>

#include <linux/init.h>

#include <linux/errno.h>

#include <linux/kernel.h>
@@ -68,7 +67,7 @@ int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb) 
	struct dccp_sock *dp = dccp_sk(sk);

	struct dccp_ackvec *av = dp->dccps_hc_rx_ackvec;

	/* Figure out how many options do we need to represent the ackvec */

	const u16 nr_opts = DIV_ROUND_UP(av->av_vec_len, DCCP_MAX_ACKVEC_OPT_LEN);

	const u8 nr_opts = DIV_ROUND_UP(av->av_vec_len, DCCP_SINGLE_OPT_MAXLEN);

	u16 len = av->av_vec_len + 2 * nr_opts, i;

	u32 elapsed_time;

	const unsigned char *tail, *from;
@@ -100,8 +99,8 @@ int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb) 
	for (i = 0; i < nr_opts; ++i) {

		int copylen = len;



		if (len > DCCP_MAX_ACKVEC_OPT_LEN)

			copylen = DCCP_MAX_ACKVEC_OPT_LEN;

		if (len > DCCP_SINGLE_OPT_MAXLEN)

			copylen = DCCP_SINGLE_OPT_MAXLEN;



		*to++ = DCCPO_ACK_VECTOR_0;

		*to++ = copylen + 2;
@@ -432,7 +431,7 @@ found: 
int dccp_ackvec_parse(struct sock *sk, const struct sk_buff *skb,

		      u64 *ackno, const u8 opt, const u8 *value, const u8 len)

{

	if (len > DCCP_MAX_ACKVEC_OPT_LEN)

	if (len > DCCP_SINGLE_OPT_MAXLEN)

		return -1;



	/* dccp_ackvector_print(DCCP_SKB_CB(skb)->dccpd_ack_seq, value, len); */

net/dccp/ackvec.h

+2 −3
Original line number Diff line number Diff line
@@ -11,15 +11,14 @@ 
 *	published by the Free Software Foundation.

 */



#include <linux/dccp.h>

#include <linux/compiler.h>

#include <linux/ktime.h>

#include <linux/list.h>

#include <linux/types.h>



/* Read about the ECN nonce to see why it is 253 */

#define DCCP_MAX_ACKVEC_OPT_LEN 253

/* We can spread an ack vector across multiple options */

#define DCCP_MAX_ACKVEC_LEN (DCCP_MAX_ACKVEC_OPT_LEN * 2)

#define DCCP_MAX_ACKVEC_LEN (DCCP_SINGLE_OPT_MAXLEN * 2)



#define DCCP_ACKVEC_STATE_RECEIVED	0

#define DCCP_ACKVEC_STATE_ECN_MARKED	(1 << 6)

net/dccp/feat.h

+2 −0
Original line number Diff line number Diff line
@@ -22,6 +22,8 @@ 
/* Wmin=32 and Wmax=2^46-1 from 7.5.2 */

#define DCCPF_SEQ_WMIN		32

#define DCCPF_SEQ_WMAX		0x3FFFFFFFFFFFull

/* Maximum number of SP values that fit in a single (Confirm) option */

#define DCCP_FEAT_MAX_SP_VALS	(DCCP_SINGLE_OPT_MAXLEN - 2)



enum dccp_feat_type {

	FEAT_AT_RX   = 1,	/* located at RX side of half-connection  */

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