path: root/Documentation
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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2006-11-10 17:43:06 -0200
committerDavid S. Miller <davem@sunset.davemloft.net>2006-12-02 21:22:09 -0800
commit6f4e5fff1e4d46714ea554fd83e44eab534e8b11 (patch)
tree4b14344fd825bbcefb6e8514e98e3e796b2dc1bd /Documentation
parenta11d206d0f88e092419877c7f706cafb5e1c2e57 (diff)
[DCCP]: Support for partial checksums (RFC 4340, sec. 9.2)
This patch does the following: a) introduces variable-length checksums as specified in [RFC 4340, sec. 9.2] b) provides necessary socket options and documentation as to how to use them c) basic support and infrastructure for the Minimum Checksum Coverage feature [RFC 4340, sec. 9.2.1]: acceptability tests, user notification and user interface In addition, it (1) fixes two bugs in the DCCPv4 checksum computation: * pseudo-header used checksum_len instead of skb->len * incorrect checksum coverage calculation based on dccph_x (2) removes dccp_v4_verify_checksum() since it reduplicates code of the checksum computation; code calling this function is updated accordingly. (3) now uses skb_checksum(), which is safer than checksum_partial() if the sk_buff has is a non-linear buffer (has pages attached to it). (4) fixes an outstanding TODO item: * If P.CsCov is too large for the packet size, drop packet and return. The code has been tested with applications, the latest version of tcpdump now comes with support for partial DCCP checksums. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Diffstat (limited to 'Documentation')
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/networking/dccp.txt b/Documentation/networking/dccp.txt
index 74563b38ffd9..a8142a81038a 100644
--- a/Documentation/networking/dccp.txt
+++ b/Documentation/networking/dccp.txt
@@ -47,6 +47,22 @@ 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.
+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
+accepted by the receiver. Hence, when using this feature on the sender, it must
+be enabled at the receiver, too with suitable choice of CsCov.
+DCCP_SOCKOPT_SEND_CSCOV sets the sender checksum coverage. Values in the
+ range 0..15 are acceptable. The default setting is 0 (full coverage),
+ values between 1..15 indicate partial coverage.
+DCCP_SOCKOPT_SEND_CSCOV is for the receiver and has a different meaning: it
+ sets a threshold, where again values 0..15 are acceptable. The default
+ of 0 means that all packets with a partial coverage will be discarded.
+ Values in the range 1..15 indicate that packets with minimally such a
+ coverage value are also acceptable. The higher the number, the more
+ restrictive this setting (see [RFC 4340, sec. 9.2.1]).