[Patch v2] net: export TCP send buffer size via netlink

[Patch v2] net: export TCP send buffer size via netlink

[Amerigo Wang]

V1 -> V2:
Keep ABI compatiblity of struct tcp_info.

Currently, we can only get TCP send buffer size by
getsockopt (SO_SNDBUF or TCP_INFO), this is not enough
for the tools like netstat or ss to read.

Show TCP send buffer size via netlink NETLINK_INET_DIAG.

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>

---

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 7fee8a4..b63f541 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -163,6 +163,8 @@ struct tcp_info {
 	__u32	tcpi_rcv_space;
 
 	__u32	tcpi_total_retrans;
+
+	__u32	tcpi_sndbuf;
 };
 
 /* for TCP_MD5SIG socket option */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b0a26bb..b3d6a62 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2385,6 +2385,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	info->tcpi_retransmits = icsk->icsk_retransmits;
 	info->tcpi_probes = icsk->icsk_probes_out;
 	info->tcpi_backoff = icsk->icsk_backoff;
+	info->tcpi_sndbuf = sk->sk_sndbuf;
 
 	if (tp->rx_opt.tstamp_ok)
 		info->tcpi_options |= TCPI_OPT_TIMESTAMPS;

Re: [Patch v2] net: export TCP send buffer size via netlink

[David Miller]

From: Amerigo Wang <amwang@redhat.com>
Date: Mon, 1 Feb 2010 04:18:28 -0500

> V1 -> V2:
> Keep ABI compatiblity of struct tcp_info.
> 
> Currently, we can only get TCP send buffer size by
> getsockopt (SO_SNDBUF or TCP_INFO), this is not enough
> for the tools like netstat or ss to read.
> 
> Show TCP send buffer size via netlink NETLINK_INET_DIAG.
> 
> Signed-off-by: WANG Cong <amwang@redhat.com>

If the user has a "struct tcp_info info" on it's stack,
and it's compiled against the header file before your
changes, guess what the kernel is going to do?

It's going to write past the end of the user's variable
into random stack locations.

You can't change the layout, at all.

Re: [Patch v2] net: export TCP send buffer size via netlink

[David Miller]

Before you spend the next couple hours trying to figure out what to
do...

We already provide the information you're trying to export via
linux/inet_diag.h:inet_diag_meminfo

I hope the light goes on now :-)

Re: [Patch v2] net: export TCP send buffer size via netlink

[Cong Wang]

David Miller wrote:
> Before you spend the next couple hours trying to figure out what to
> do...
> 
> We already provide the information you're trying to export via
> linux/inet_diag.h:inet_diag_meminfo
> 
> I hope the light goes on now :-)
> 

Oh, I was just looking for a pointer.

Ok, ->idiag_wmem is gotten from sk->sk_wmem_queued, so ->sk_wmem_queued
is the TCP send buffer size that we want? I thought it is ->sk_sndbuf...

Thanks for your help!