[DCCP]: Add socket option to query the current MPS
This enables applications to query the current value of the Maximum
Packet Size via a socket option, suggested as a SHOULD in (RFC 4340,
p. 102).
This socket option is useful to avoid the annoying bail-out via
`-EMSGSIZE'. In particular, as fragmentation is not currently
supported (and its use is partly discouraged in RFC 4340).
With this option, it is possible to size buffers accordingly, e.g.
int buflen = dccp_get_cur_mps(sockfd);
/* or */
if (msgsize > dccp_get_cur_mps(sockfd))
die("message is too large for this path");
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/dccp.h b/include/linux/dccp.h
index 4ed82e2..0e44a3e 100644
--- a/include/linux/dccp.h
+++ b/include/linux/dccp.h
@@ -202,6 +202,7 @@
#define DCCP_SOCKOPT_SERVICE 2
#define DCCP_SOCKOPT_CHANGE_L 3
#define DCCP_SOCKOPT_CHANGE_R 4
+#define DCCP_SOCKOPT_GET_CUR_MPS 5
#define DCCP_SOCKOPT_SEND_CSCOV 10
#define DCCP_SOCKOPT_RECV_CSCOV 11
#define DCCP_SOCKOPT_CCID_RX_INFO 128