[PATCH 1/1] tcp: Replace constants with #define macros

    to record the state of SACK/FACK and DSACK for better readability and maintenance.

Signed-off-by: Vijay Subramanian <redacted>
---
 include/linux/tcp.h   |    5 +++++
 include/net/tcp.h     |    4 ++--
 net/ipv4/syncookies.c |    2 +-
 net/ipv4/tcp_input.c  |    6 +++---
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 7f59ee9..874b043 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h

@@ -238,6 +238,11 @@ struct tcp_sack_block {
 	u32	end_seq;
 };
 
+/*These are used to set the sack_ok field in struct tcp_options_received */
+#define SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
+#define FACK_ENABLED  (1 << 1)   /*1 = FACK is enabled locally*/
+#define DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from peer*/
+
 struct tcp_options_received {
 /*	PAWS/RTTM data	*/
 	long	ts_recent_stamp;/* Time we stored ts_recent (for aging) */

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a4f52e1..cbb943e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -773,12 +773,12 @@ static inline int tcp_is_reno(const struct tcp_sock *tp)
 
 static inline int tcp_is_fack(const struct tcp_sock *tp)
 {
-	return tp->rx_opt.sack_ok & 2;
+	return tp->rx_opt.sack_ok & FACK_ENABLED;
 }
 
 static inline void tcp_enable_fack(struct tcp_sock *tp)
 {
-	tp->rx_opt.sack_ok |= 2;
+	tp->rx_opt.sack_ok |= FACK_ENABLED;
 }
 
 static inline unsigned int tcp_left_out(const struct tcp_sock *tp)

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 90f6544..dfba6a5 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c

@@ -245,7 +245,7 @@ bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, bool *ecn_ok)
 	if (!sysctl_tcp_timestamps)
 		return false;
 
-	tcp_opt->sack_ok = (options >> 4) & 0x1;
+	tcp_opt->sack_ok = (options >> 4) & SACK_SEEN;
 	*ecn_ok = (options >> 5) & 1;
 	if (*ecn_ok && !sysctl_tcp_ecn)
 		return false;

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f131d92..5cbc788 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -865,13 +865,13 @@ static void tcp_disable_fack(struct tcp_sock *tp)
 	/* RFC3517 uses different metric in lost marker => reset on change */
 	if (tcp_is_fack(tp))
 		tp->lost_skb_hint = NULL;
-	tp->rx_opt.sack_ok &= ~2;
+	tp->rx_opt.sack_ok &= ~FACK_ENABLED;
 }
 
 /* Take a notice that peer is sending D-SACKs */
 static void tcp_dsack_seen(struct tcp_sock *tp)
 {
-	tp->rx_opt.sack_ok |= 4;
+	tp->rx_opt.sack_ok |= DSACK_SEEN;
 }
 
 /* Initialize metrics on socket. */

@@ -3878,7 +3878,7 @@ void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *o
 			case TCPOPT_SACK_PERM:
 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
 				    !estab && sysctl_tcp_sack) {
-					opt_rx->sack_ok = 1;
+					opt_rx->sack_ok = SACK_SEEN;
 					tcp_sack_reset(opt_rx);
 				}
 				break;

-- 
1.7.0.4

On 19 December 2011 19:32, Vijay Subramanian
[off-list ref] wrote:

This patch was created against net-next tree and not -net tree.
Apologies for the error. Should I resend it?

Regards,
Vijay

Since that is a fairly public header, some namespace protection
might be sensible.

-	tcp_opt->sack_ok = (options >> 4) & 0x1;
+	tcp_opt->sack_ok = (options >> 4) & SACK_SEEN;

Looks to me like that 0x1 isn't SAC_SEEK! So this is now misleading.

	David

Thanks a lot for reviewing the patch. Please see responses below.

On 20 December 2011 02:27, David Laight [off-list ref] wrote:

quoted

+/*These are used to set the sack_ok field in struct
tcp_options_received */
+#define SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
+#define FACK_ENABLED  (1 << 1)   /*1 = FACK is enabled locally*/
+#define DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from peer*/
+

Since that is a fairly public header, some namespace protection
might be sensible.

I assume you are talking about collision with userspace.  These
definitions are already protected by #ifdef  __KERNEL__.
That should be enough to protect against collisions with userspace I think.

quoted

-     tcp_opt->sack_ok = (options >> 4) & 0x1;
+     tcp_opt->sack_ok = (options >> 4) & SACK_SEEN;

Looks to me like that 0x1 isn't SAC_SEEK! So this is now misleading.

Can you please elaborate? Are you saying this is wrong or that it
could be done better?

Thanks for your time!
Vijay

From: Vijay Subramanian <redacted>
Date: Tue, 20 Dec 2011 12:02:52 -0800

I assume you are talking about collision with userspace.  These
definitions are already protected by #ifdef  __KERNEL__.
That should be enough to protect against collisions with userspace I think.

Within the kernel he means, please put a TCP_* prefix onto these
values.

quoted

quoted

-     tcp_opt->sack_ok = (options >> 4) & 0x1;
+     tcp_opt->sack_ok = (options >> 4) & SACK_SEEN;

Looks to me like that 0x1 isn't SAC_SEEK! So this is now misleading.

Can you please elaborate? Are you saying this is wrong or that it
could be done better?

I think he's saying it could be done better.  Probably something
like:

	tcp_opt->sack_ok = (options & (1 << 4)) ? SACK_SEEN : 0;

quoted

I assume you are talking about collision with userspace.  These
definitions are already protected by #ifdef  __KERNEL__.
That should be enough to protect against collisions with 

userspace I think.

Within the kernel he means, please put a TCP_* prefix onto these
values.

Given the values are currently:

quoted

+#define SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
+#define FACK_ENABLED  (1 << 1)   /*1 = FACK is enabled locally*/
+#define DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from

peer*/

But the structure field member is 'sack_ok', unless it generates
very silly long lines - which in this case it probably doesn't -
it might even be worth prefixing with TCP_SACK_OK_ although
that might be deemed excessive!

	David

Given the values are currently:

quoted

quoted

+#define SACK_SEEN     (1 << 0)   /*1 = peer is SACK capable, */
+#define FACK_ENABLED  (1 << 1)   /*1 = FACK is enabled locally*/
+#define DSACK_SEEN    (1 << 2)   /*1 = DSACK was received from

peer*/

But the structure field member is 'sack_ok', unless it generates
very silly long lines - which in this case it probably doesn't -
it might even be worth prefixing with TCP_SACK_OK_ although
that might be deemed excessive!

Thanks for all the feedback. I will follow these suggestions in future.

Vijay