From 7c559a9e44ee61faf2f339604ce708decb345a93 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Thu, 4 Oct 2007 14:39:22 -0700 Subject: [PATCH] [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 Signed-off-by: Ian McDonald Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: David S. Miller --- Documentation/networking/dccp.txt | 3 +++ include/linux/dccp.h | 1 + net/dccp/proto.c | 4 ++++ 3 files changed, 8 insertions(+) diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt index 477026ae0f..f9157180f7 100644 --- a/Documentation/networking/dccp.txt +++ b/Documentation/networking/dccp.txt @@ -41,6 +41,9 @@ the socket will fall back to 0 (which means that no meaningful service code is present). Connecting sockets set at most one service option; for listening sockets, multiple service codes can be specified. +DCCP_SOCKOPT_GET_CUR_MPS is read-only and retrieves the current maximum packet +size (application payload size) in bytes, see RFC 4340, section 14. + DCCP_SOCKOPT_SEND_CSCOV and DCCP_SOCKOPT_RECV_CSCOV are used for setting the partial checksum coverage (RFC 4340, sec. 9.2). The default is that checksums always cover the entire packet and that only fully covered application data is diff --git a/include/linux/dccp.h b/include/linux/dccp.h index 4ed82e2c9f..0e44a3e520 100644 --- a/include/linux/dccp.h +++ b/include/linux/dccp.h @@ -202,6 +202,7 @@ struct dccp_so_feat { #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 diff --git a/net/dccp/proto.c b/net/dccp/proto.c index 7e4f54a4ec..c0b685efe2 100644 --- a/net/dccp/proto.c +++ b/net/dccp/proto.c @@ -587,6 +587,10 @@ static int do_dccp_getsockopt(struct sock *sk, int level, int optname, case DCCP_SOCKOPT_SERVICE: return dccp_getsockopt_service(sk, len, (__be32 __user *)optval, optlen); + case DCCP_SOCKOPT_GET_CUR_MPS: + val = dp->dccps_mss_cache; + len = sizeof(val); + break; case DCCP_SOCKOPT_SEND_CSCOV: val = dp->dccps_pcslen; len = sizeof(val); -- 2.39.5