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net: tcp: Use our MTU to determine the mss for transmission

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In the existing the value received from the other side by the TCP options
is used as MSS for transmission. Since the MSS options are an
announcement rather then a negotionation, it is likely the receiver will
have a different and possibly bigger MSS than allowed by our side.
This allow potentially for different a MSS in the receive and transmit
path.

Directly using the received MSS could cause problems when our MSS is only
allowed to be small. At transmission, for that reason take the minimum of
the received MSS and our desired MSS to find a value compatible to both
sides of the link.

Rename the function to net_tcp_get_recv_mss to net_tcp_get_supported_mss
to better reflect its function in the new situation.

Signed-off-by: Sjors Hettinga <s.a.hettinga@gmail.com>
This commit is contained in:
Sjors Hettinga 2022-05-23 08:36:28 +02:00 committed by Carles Cufí
parent cf59606883
commit f5679ab73e
4 changed files with 7 additions and 6 deletions
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2
subsys/net/ip/net_shell.c
View file

@ -1468,7 +1468,7 @@ static void tcp_cb(struct tcp *conn, void *user_data)
struct net_shell_user_data *data = user_data;
const struct shell *shell = data->shell;
int *count = data->user_data;
uint16_t recv_mss = net_tcp_get_recv_mss(conn);
uint16_t recv_mss = net_tcp_get_supported_mss(conn);
PR("%p %p %5u %5u %10u %10u %5u %s\n",
conn, conn->context,

4
subsys/net/ip/tcp.c
View file

@ -836,7 +836,7 @@ static int net_tcp_set_mss_opt(struct tcp *conn, struct net_pkt *pkt)
return -ENOBUFS;
}
recv_mss = net_tcp_get_recv_mss(conn);
recv_mss = net_tcp_get_supported_mss(conn);
recv_mss |= (NET_TCP_MSS_OPT << 24) | (NET_TCP_MSS_SIZE << 16);
UNALIGNED_PUT(htonl(recv_mss), (uint32_t *)mss);
@ -2916,7 +2916,7 @@ void net_tcp_foreach(net_tcp_cb_t cb, void *user_data)
k_mutex_unlock(&tcp_lock);
}
uint16_t net_tcp_get_recv_mss(const struct tcp *conn)
uint16_t net_tcp_get_supported_mss(const struct tcp *conn)
{
sa_family_t family = net_context_get_family(conn->context);

4
subsys/net/ip/tcp_internal.h
View file

@ -38,9 +38,9 @@ extern "C" {
* @return Maximum Segment Size
*/
#if defined(CONFIG_NET_NATIVE_TCP)
uint16_t net_tcp_get_recv_mss(const struct tcp *conn);
uint16_t net_tcp_get_supported_mss(const struct tcp *conn);
#else
static inline uint16_t net_tcp_get_recv_mss(const struct tcp *conn)
static inline uint16_t net_tcp_get_supported_mss(const struct tcp *conn)
{
ARG_UNUSED(conn);
return 0;

3
subsys/net/ip/tcp_private.h
View file

@ -112,7 +112,8 @@
#define conn_mss(_conn) \
((_conn)->recv_options.mss_found ? \
(_conn)->recv_options.mss : (uint16_t)NET_IPV6_MTU)
MIN((_conn)->recv_options.mss, \
net_tcp_get_supported_mss(_conn)) : net_tcp_get_supported_mss(_conn))
#define conn_state(_conn, _s) \
({ \