Hi Tomasz, | Since packets with invalid cmsg parameters can be rejected by kernel there | is a need to allow applications to access information on available policies | and their respective cmsg parameters at runtime. This patch simplifies | maintaining compatibility between userspace applications and DCCP code. | The difference to querying supported CCIDs is that * CCIDs are all defined per RFC documents, and that * different combinations of CCIDs are possible due to the Kconfig options. As far as I understand your patch, querying here has a different role - ensuring compatibilities between kernel versions. I think it might be too early for that: * it takes quite a long while until patches propagate through to mainline (more than half a year), so that there is the time to come up with a single, well-tested interface; * at this stage it would be better to have documentation (man pages, web pages, sample application code etc.) to allow people to use the interface - few will want to discover the interface by grepping through source code. DCCP is full of half-finished things. I would much prefer to keep this as simple as at all possible, to have time/room to fix the missing parts (such as no ECN support) in DCCP. As a possible suggestion, I came up with a minimalistic variant of querying the interface - only 7 lines, including documentation. This is attached and it works by exploiting that * policy IDs are just numbers; * so that we could use the highest supported ID instead of an array; * parameters are tied to the individual policy, so that a second query (about which parameters are supported) is not necessary. I have put this idea as a suggestion into the `qpolicy' subtree at git://eden-feed.erg.abdn.ac.uk/dccp_exp A trivial test program using this interface can be downloaded from http://www.erg.abdn.ac.uk/users/gerrit/dccp/query_ids.tar.gz - Gerrit
This is a smaller diff, combined from the two patches currently in the qpolicy subtree. -- Documentation/networking/dccp.txt | 3 +++ include/linux/dccp.h | 1 + net/dccp/proto.c | 3 +++ 3 files changed, 7 insertions(+) --- a/Documentation/networking/dccp.txt +++ b/Documentation/networking/dccp.txt @@ -45,6 +45,9 @@ http://linux-net.osdl.org/index.php/DCCP Socket options ============== +DCCP_SOCKOPT_QPOLICY_AVAILABLE returns the highest supported policy number. The +policy IDs start with 0 (default policy) and are consecutively numbered. + DCCP_SOCKOPT_QPOLICY_ID sets the dequeuing policy for outgoing packets. It takes a policy ID as argument and can only be set before the connection (i.e. changes during an established connection are not supported). Currently, two policies are --- a/include/linux/dccp.h +++ b/include/linux/dccp.h @@ -223,6 +223,7 @@ enum dccp_packet_dequeueing_policy { #define DCCP_SOCKOPT_RX_CCID 15 #define DCCP_SOCKOPT_QPOLICY_ID 16 #define DCCP_SOCKOPT_QPOLICY_TXQLEN 17 +#define DCCP_SOCKOPT_QPOLICY_AVAILABLE 18 #define DCCP_SOCKOPT_CCID_RX_INFO 128 #define DCCP_SOCKOPT_CCID_TX_INFO 192 --- a/net/dccp/proto.c +++ b/net/dccp/proto.c @@ -666,6 +666,9 @@ static int do_dccp_getsockopt(struct soc case DCCP_SOCKOPT_QPOLICY_TXQLEN: val = dp->dccps_tx_qlen; break; + case DCCP_SOCKOPT_QPOLICY_AVAILABLE: + val = DCCPQ_POLICY_MAX - 1; + break; case 128 ... 191: return ccid_hc_rx_getsockopt(dp->dccps_hc_rx_ccid, sk, optname, len, (u32 __user *)optval, optlen);
