[PATCH net-next 1/3] net: tcp: add sysctl for controling tcp window shrink

[menglong8.dong@gmail.com]

From: Menglong Dong <imagedong@tencent.com>

Introduce the sysctl 'tcp_wnd_shrink', which will be used in the
following patches.

Signed-off-by: Menglong Dong <imagedong@tencent.com>
---
 include/net/tcp.h          | 1 +
 net/ipv4/sysctl_net_ipv4.c | 9 +++++++++
 net/ipv4/tcp.c             | 3 +++
 3 files changed, 13 insertions(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a0a91a988272..a6cf6d823e34 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -247,6 +247,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
 /* sysctl variables for tcp */
 extern int sysctl_tcp_max_orphans;
 extern long sysctl_tcp_mem[3];
+extern int sysctl_tcp_wnd_shrink;
 
 #define TCP_RACK_LOSS_DETECTION  0x1 /* Use RACK to detect losses */
 #define TCP_RACK_STATIC_REO_WND  0x2 /* Use static RACK reo wnd */
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 0d0cc4ef2b85..fd6cb5a5c2b9 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -577,6 +577,15 @@ static struct ctl_table ipv4_table[] = {
 		.extra1		= &sysctl_fib_sync_mem_min,
 		.extra2		= &sysctl_fib_sync_mem_max,
 	},
+	{
+		.procname       = "tcp_wnd_shrink",
+		.data           = &sysctl_tcp_wnd_shrink,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec_minmax,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE
+	},
 	{ }
 };
 
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index fd68d49490f2..db0483b2159f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -297,6 +297,9 @@ EXPORT_SYMBOL(tcp_memory_allocated);
 DEFINE_PER_CPU(int, tcp_memory_per_cpu_fw_alloc);
 EXPORT_PER_CPU_SYMBOL_GPL(tcp_memory_per_cpu_fw_alloc);
 
+int sysctl_tcp_wnd_shrink __read_mostly;
+EXPORT_SYMBOL(sysctl_tcp_wnd_shrink);
+
 #if IS_ENABLED(CONFIG_SMC)
 DEFINE_STATIC_KEY_FALSE(tcp_have_smc);
 EXPORT_SYMBOL(tcp_have_smc);
-- 
2.40.1