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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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29
src/net/tcpip.c
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@@ -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
*