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tcp: add tcp_mss_clamp() helper 

Small cleanup factorizing code doing the TCP_MAXSEG clamping.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2017-02-02 08:04:56 -08:00 committed by David S. Miller
parent ff3edc9b8e
commit 3541f9e8bd
5 changed files with 17 additions and 23 deletions
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9
include/linux/tcp.h
View File

@ -445,4 +445,13 @@ static inline void tcp_saved_syn_free(struct tcp_sock *tp)
struct sk_buff *tcp_get_timestamping_opt_stats(const struct sock *sk);
static inline u16 tcp_mss_clamp(const struct tcp_sock *tp, u16 mss)
{
/* We use READ_ONCE() here because socket might not be locked.
* This happens for listeners.
*/
u16 user_mss = READ_ONCE(tp->rx_opt.user_mss);
return (user_mss && user_mss < mss) ? user_mss : mss;
}
#endif /* _LINUX_TCP_H */

5
net/ipv4/tcp_ipv4.c
View File

@ -1324,10 +1324,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
tcp_ca_openreq_child(newsk, dst);
tcp_sync_mss(newsk, dst_mtu(dst));
newtp->advmss = dst_metric_advmss(dst);
if (tcp_sk(sk)->rx_opt.user_mss &&
tcp_sk(sk)->rx_opt.user_mss < newtp->advmss)
newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;
newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
tcp_initialize_rcv_mss(newsk);

7
net/ipv4/tcp_minisocks.c
View File

@ -360,15 +360,12 @@ void tcp_openreq_init_rwin(struct request_sock *req,
{
struct inet_request_sock *ireq = inet_rsk(req);
const struct tcp_sock *tp = tcp_sk(sk_listener);
u16 user_mss = READ_ONCE(tp->rx_opt.user_mss);
int full_space = tcp_full_space(sk_listener);
int mss = dst_metric_advmss(dst);
u32 window_clamp;
__u8 rcv_wscale;
int mss;
if (user_mss && user_mss < mss)
mss = user_mss;
mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
window_clamp = READ_ONCE(tp->window_clamp);
/* Set this up on the first call only */
req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW);

14
net/ipv4/tcp_output.c
View File

@ -3062,7 +3062,6 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
struct sk_buff *skb;
int tcp_header_size;
struct tcphdr *th;
u16 user_mss;
int mss;
skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
@ -3092,10 +3091,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
}
skb_dst_set(skb, dst);
mss = dst_metric_advmss(dst);
user_mss = READ_ONCE(tp->rx_opt.user_mss);
if (user_mss && user_mss < mss)
mss = user_mss;
mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
memset(&opts, 0, sizeof(opts));
#ifdef CONFIG_SYN_COOKIES
@ -3201,9 +3197,7 @@ static void tcp_connect_init(struct sock *sk)
if (!tp->window_clamp)
tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
tp->advmss = dst_metric_advmss(dst);
if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
tp->advmss = tp->rx_opt.user_mss;
tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
tcp_initialize_rcv_mss(sk);
@ -3280,8 +3274,8 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
* user-MSS. Reserve maximum option space for middleboxes that add
* private TCP options. The cost is reduced data space in SYN :(
*/
if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp);
space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
MAX_TCP_OPTION_SPACE;

5
net/ipv6/tcp_ipv6.c
View File

@ -1147,10 +1147,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
tcp_ca_openreq_child(newsk, dst);
tcp_sync_mss(newsk, dst_mtu(dst));
newtp->advmss = dst_metric_advmss(dst);
if (tcp_sk(sk)->rx_opt.user_mss &&
tcp_sk(sk)->rx_opt.user_mss < newtp->advmss)
newtp->advmss = tcp_sk(sk)->rx_opt.user_mss;
newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
tcp_initialize_rcv_mss(newsk);