[PATCH] TCP: Add seq and ack numbers to TCP_INFO

[PATCH] TCP: Add seq and ack numbers to TCP_INFO

[Adam Langley]

TCP: Add seq and ack numbers to TCP_INFO

No ABI breakage: Userspace specifies the size of the structure that they're
expecting, and the new fields are at the end, so existing code should function
just fine as we'll truncate the new struct tcp_info to fit.

Signed-off-by: Adam Langley <agl@imperialviolet.org>
---

 include/linux/tcp.h |    5 +++++
 net/ipv4/tcp.c      |    5 +++++
 2 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 07e79bd..55094ea 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -157,6 +157,11 @@ struct tcp_info
 	__u32	tcpi_rcv_space;
 
 	__u32	tcpi_total_retrans;
+
+	__u32	tcpi_seq; /* seq number of next byte to be written to socket */
+	__u32	tcpi_ack; /* ack number of next byte to be read from socket */
+	__u32	tcpi_tseq; /* seq number of next byte to be transmitted */
+	__u32	tcpi_tack; /* ack number of next byte to be received */
 };
 
 /* for TCP_MD5SIG socket option */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 56a133c..c56d5c3 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2255,6 +2255,11 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	info->tcpi_rcv_space = tp->rcvq_space.space;
 
 	info->tcpi_total_retrans = tp->total_retrans;
+
+	info->tcpi_seq = tp->write_seq;
+	info->tcpi_ack = tp->copied_seq;
+	info->tcpi_tseq = tp->pushed_seq;
+	info->tcpi_tack = tp->rcv_nxt;
 }
 
 EXPORT_SYMBOL_GPL(tcp_get_info);

Re: [PATCH] TCP: Add seq and ack numbers to TCP_INFO

[Stephen Hemminger]

On Wed, 9 Jul 2008 10:23:43 -0700
"Adam Langley" <agl@imperialviolet.org> wrote:

> TCP: Add seq and ack numbers to TCP_INFO
> 
> No ABI breakage: Userspace specifies the size of the structure that they're
> expecting, and the new fields are at the end, so existing code should function
> just fine as we'll truncate the new struct tcp_info to fit.
> 
> Signed-off-by: Adam Langley <agl@imperialviolet.org>

Of what possible use is this to an application? I worry that applications would
come to expect or use certain characteristics of the network and TCP which
would be broken by later changes.

Re: [PATCH] TCP: Add seq and ack numbers to TCP_INFO

[Adam Langley]

On Wed, Jul 9, 2008 at 10:49 AM, Stephen Hemminger
<stephen.hemminger@vyatta.com> wrote:
> Of what possible use is this to an application? I worry that applications would
> come to expect or use certain characteristics of the network and TCP which
> would be broken by later changes.

Well, when you consider what else is in tcp_info (window scaling, SACK
info, MTU, RTT, reorder detection), the sequence numbers seem
positively pedestrian.

There are a bunch of crazy reasons why userspace might be interested
in the seq/ack numbers: handing connections between hosts, checking
the backlog, analyzing the RNG strength of remote hosts etc. All
experimental crap to be sure, but it's very handy in those
experiments. I used a very similar patch when doing some of the very
early basic on backlogs that Jerry Chu has taken up now.

And sequence numbers are pretty fundamental to TCP. Certainly much
more so than much of the other stuff that we're currently happy to
export with sufficient warnings.


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org