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[tcpip] Provide tcpip_mtu() to determine the maximum transmission unit

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Provide the function tcpip_mtu() to allow external code to determine
the (transport-layer) maximum transmission unit for a given socket
address.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown 2014-03-04 13:10:07 +00:00
parent db67de6f31
commit 6414b5ca03
4 changed files with 34 additions and 0 deletions
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3
src/include/ipxe/tcpip.h
View File

@ -97,6 +97,8 @@ struct tcpip_net_protocol {
const char *name;
/** Network address family */
sa_family_t sa_family;
/** Fixed header length */
size_t header_len;
/**
* Transmit packet
*
@ -148,6 +150,7 @@ extern int tcpip_tx ( struct io_buffer *iobuf, struct tcpip_protocol *tcpip,
struct net_device *netdev,
uint16_t *trans_csum );
extern struct net_device * tcpip_netdev ( struct sockaddr_tcpip *st_dest );
extern size_t tcpip_mtu ( struct sockaddr_tcpip *st_dest );
extern uint16_t generic_tcpip_continue_chksum ( uint16_t partial,
const void *data, size_t len );
extern uint16_t tcpip_chksum ( const void *data, size_t len );

1
src/net/ipv4.c
View File

@ -621,6 +621,7 @@ struct net_protocol ipv4_protocol __net_protocol = {
struct tcpip_net_protocol ipv4_tcpip_protocol __tcpip_net_protocol = {
.name = "IPv4",
.sa_family = AF_INET,
.header_len = sizeof ( struct iphdr ),
.tx = ipv4_tx,
.netdev = ipv4_netdev,
};

1
src/net/ipv6.c
View File

@ -988,6 +988,7 @@ struct net_protocol ipv6_protocol __net_protocol = {
struct tcpip_net_protocol ipv6_tcpip_protocol __tcpip_net_protocol = {
.name = "IPv6",
.sa_family = AF_INET6,
.header_len = sizeof ( struct ipv6_header ),
.tx = ipv6_tx,
.netdev = ipv6_netdev,
};

29
src/net/tcpip.c
View File

@ -6,6 +6,7 @@
#include <ipxe/iobuf.h>
#include <ipxe/tables.h>
#include <ipxe/ipstat.h>
#include <ipxe/netdevice.h>
#include <ipxe/tcpip.h>
/** @file
@ -122,6 +123,34 @@ struct net_device * tcpip_netdev ( struct sockaddr_tcpip *st_dest ) {
return NULL;
}
/**
* Determine maximum transmission unit
*
* @v st_dest Destination address
* @ret mtu Maximum transmission unit
*/
size_t tcpip_mtu ( struct sockaddr_tcpip *st_dest ) {
struct tcpip_net_protocol *tcpip_net;
struct net_device *netdev;
size_t mtu;
/* Find appropriate network-layer protocol */
tcpip_net = tcpip_net_protocol ( st_dest );
if ( ! tcpip_net )
return 0;
/* Find transmitting network device */
netdev = tcpip_net->netdev ( st_dest );
if ( ! netdev )
return 0;
/* Calculate MTU */
mtu = ( netdev->max_pkt_len - netdev->ll_protocol->ll_header_len -
tcpip_net->header_len );
return mtu;
}
/**
* Calculate continued TCP/IP checkum
*