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sd-dhcp-client: allow the max dhcp message size to be set to the MTU of the link

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This commit is contained in:
Tom Gundersen 2014-08-01 16:10:13 +02:00
parent c18126e8da
commit 324f818781
3 changed files with 29 additions and 2 deletions
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3
src/libsystemd-network/dhcp-protocol.h
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@ -60,7 +60,8 @@ typedef struct DHCPPacket DHCPPacket;
#define DHCP_IP_SIZE (int32_t)(sizeof(struct iphdr))
#define DHCP_IP_UDP_SIZE (int32_t)(sizeof(struct udphdr) + DHCP_IP_SIZE)
#define DHCP_MESSAGE_SIZE (int32_t)(sizeof(DHCPMessage))
#define DHCP_MIN_OPTIONS_SIZE 308 /* spec says 312, but that includes the magic cookie */
#define DHCP_DEFAULT_MIN_SIZE 576 /* the minimum internet hosts must be able to receive */
#define DHCP_MIN_OPTIONS_SIZE DHCP_DEFAULT_MIN_SIZE - DHCP_IP_UDP_SIZE - DHCP_MESSAGE_SIZE
#define DHCP_MAGIC_COOKIE (uint32_t)(0x63825363)
enum {

27
src/libsystemd-network/sd-dhcp-client.c
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@ -59,6 +59,7 @@ struct sd_dhcp_client {
} _packed_ client_id;
char *hostname;
char *vendor_class_identifier;
uint32_t mtu;
uint32_t xid;
usec_t start_time;
uint16_t secs;
@ -227,6 +228,15 @@ int sd_dhcp_client_set_vendor_class_identifier(sd_dhcp_client *client,
return 0;
}
int sd_dhcp_client_set_mtu(sd_dhcp_client *client, uint32_t mtu) {
assert_return(client, -EINVAL);
assert_return(mtu >= DHCP_DEFAULT_MIN_SIZE, -ERANGE);
client->mtu = mtu;
return 0;
}
int sd_dhcp_client_get_lease(sd_dhcp_client *client, sd_dhcp_lease **ret) {
assert_return(client, -EINVAL);
assert_return(ret, -EINVAL);
@ -366,9 +376,23 @@ static int client_message_init(sd_dhcp_client *client, DHCPPacket **ret,
Note (from ConnMan): Some DHCP servers will send bigger DHCP packets
than the defined default size unless the Maximum Messge Size option
is explicitely set
RFC3442 "Requirements to Avoid Sizing Constraints":
Because a full routing table can be quite large, the standard 576
octet maximum size for a DHCP message may be too short to contain
some legitimate Classless Static Route options. Because of this,
clients implementing the Classless Static Route option SHOULD send a
Maximum DHCP Message Size [4] option if the DHCP client's TCP/IP
stack is capable of receiving larger IP datagrams. In this case, the
client SHOULD set the value of this option to at least the MTU of the
interface that the client is configuring. The client MAY set the
value of this option higher, up to the size of the largest UDP packet
it is prepared to accept. (Note that the value specified in the
Maximum DHCP Message Size option is the total maximum packet size,
including IP and UDP headers.)
*/
max_size = htobe16(size);
r = dhcp_option_append(&packet->dhcp, optlen, &optoffset, 0,
r = dhcp_option_append(&packet->dhcp, client->mtu, &optoffset, 0,
DHCP_OPTION_MAXIMUM_MESSAGE_SIZE,
2, &max_size);
if (r < 0)
@ -1505,6 +1529,7 @@ int sd_dhcp_client_new(sd_dhcp_client **ret) {
client->index = -1;
client->fd = -1;
client->attempt = 1;
client->mtu = DHCP_DEFAULT_MIN_SIZE;
client->req_opts_size = ELEMENTSOF(default_req_opts);

1
src/systemd/sd-dhcp-client.h
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@ -51,6 +51,7 @@ int sd_dhcp_client_set_request_broadcast(sd_dhcp_client *client, int broadcast);
int sd_dhcp_client_set_index(sd_dhcp_client *client, int interface_index);
int sd_dhcp_client_set_mac(sd_dhcp_client *client,
const struct ether_addr *addr);
int sd_dhcp_client_set_mtu(sd_dhcp_client *client, uint32_t mtu);
int sd_dhcp_client_set_hostname(sd_dhcp_client *client, const char *hostname);
int sd_dhcp_client_set_vendor_class_identifier(sd_dhcp_client *client, const char *vci);
int sd_dhcp_client_get_lease(sd_dhcp_client *client, sd_dhcp_lease **ret);