Commit:     e333b3edc489151afda2a4f6c798842c64cb67a4
Parent:     ebe6f7e73c3efec1de295205806b4550fcb468cd
Author:     Gerrit Renker <[EMAIL PROTECTED]>
AuthorDate: Wed Nov 21 10:09:56 2007 -0200
Committer:  David S. Miller <[EMAIL PROTECTED]>
CommitDate: Mon Jan 28 14:54:46 2008 -0800

    [DCCP]: Promote CCID2 as default CCID
    This patch addresses the following problems:
     1. DCCP relies for its proper functioning on having at least one CCID 
        enabled (as in TCP plugable congestion control). Currently it is 
possible to
        disable both CCIDs and thus leave the DCCP module in a compiled, but 
        non-functional state: no sockets can be created when no CCID is 
        Furthermore, the protocol is (again like TCP) not intended to be used 
        CCIDs. Last, a non-empty CCID list is needed for doing CCID feature 
     2. Internally the default CCID that is advertised by the Linux host is set 
to CCID2
        (DCCPF_INITIAL_CCID in include/linux/dccp.h). Disabling CCID2 in the 
        menu without changing the defaults leads to a failure `module not 
found' when
        trying to load the dccp module (which internally tries to load the 
default CCID).
     3. The specification (RFC 4340, sec. 10) treats CCID2 somewhat like a
        `minimum common denominator'; the specification says that:
        * "New connections start with CCID 2 for both endpoints"
        * "A DCCP implementation intended for general use, such as an 
implementation in a
           general-purpose operating system kernel, SHOULD implement at least 
           The intent is to make CCID 2 broadly available for interoperability 
        Providing CCID2 as minimum-required CCID (like Reno/Cubic in TCP) thus 
seems reasonable.
    Hence this patch automatically selects CCID2 when DCCP is enabled. 
Documentation also added.
    Discussions with Ian McDonald on this subject are gratefully acknowledged.
    Signed-off-by: Gerrit Renker <[EMAIL PROTECTED]>
    Signed-off-by: Ian McDonald <[EMAIL PROTECTED]>
    Signed-off-by: Arnaldo Carvalho de Melo <[EMAIL PROTECTED]>
    Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
 Documentation/networking/dccp.txt |   11 +++++++++--
 net/dccp/Kconfig                  |    1 +
 net/dccp/ccids/Kconfig            |   13 ++-----------
 3 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/Documentation/networking/dccp.txt 
index fdc93be..ffb9ca9 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -14,8 +14,15 @@ Introduction
 Datagram Congestion Control Protocol (DCCP) is an unreliable, connection
-based protocol designed to solve issues present in UDP and TCP particularly
-for real time and multimedia traffic.
+oriented protocol designed to solve issues present in UDP and TCP, particularly
+for real-time and multimedia (streaming) traffic.
+It divides into a base protocol (RFC 4340) and plugable congestion control
+modules called CCIDs. Like plugable TCP congestion control, at least one CCID
+needs to be enabled in order for the protocol to function properly. In the 
+implementation, this is the TCP-like CCID2 (RFC 4341). Additional CCIDs, such 
+the TCP-friendly CCID3 (RFC 4342), are optional.
+For a brief introduction to CCIDs and suggestions for choosing a CCID to match
+given applications, see section 10 of RFC 4340.
 It has a base protocol and pluggable congestion control IDs (CCIDs).
diff --git a/net/dccp/Kconfig b/net/dccp/Kconfig
index 0549e47..7aa2a7a 100644
--- a/net/dccp/Kconfig
+++ b/net/dccp/Kconfig
@@ -1,6 +1,7 @@
 menuconfig IP_DCCP
        tristate "The DCCP Protocol (EXPERIMENTAL)"
        depends on INET && EXPERIMENTAL
+       select IP_DCCP_CCID2
          Datagram Congestion Control Protocol (RFC 4340)
diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig
index 80f4698..f37af17 100644
--- a/net/dccp/ccids/Kconfig
+++ b/net/dccp/ccids/Kconfig
@@ -20,18 +20,9 @@ config IP_DCCP_CCID2
          to the user.  For example, a hypothetical application that
          transferred files over DCCP, using application-level retransmissions
          for lost packets, would prefer CCID 2 to CCID 3.  On-line games may
-         also prefer CCID 2.
+         also prefer CCID 2.  See RFC 4341 for further details.
-         CCID 2 is further described in RFC 4341,
-         This text was extracted from RFC 4340 (sec. 10.1),
-         To compile this CCID as a module, choose M here: the module will be
-         called dccp_ccid2.
-         If in doubt, say M.
+         CCID2 is the default CCID used by DCCP.
          bool "CCID2 debugging messages"
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