dccp: Initialisation and type-checking of feature sysctls

This patch takes care of initialising and type-checking sysctls related to
feature negotiation. Type checking is important since some of the sysctls
now directly act on the feature-negotiation process.

The sysctls are initialised with the known default values for each feature.
For the type-checking the value constraints from RFC 4340 are used:

 * Sequence Window uses the specified Wmin=32, the maximum is ulong (4 bytes),
   tested and confirmed that it works up to 4294967295 - for Gbps speed;
 * Ack Ratio is between 0 .. 0xffff (2-byte unsigned integer);
 * CCIDs are between 0 .. 255;
 * request_retries, retries1, retries2 also between 0..255 for good measure;
 * tx_qlen is checked to be non-negative;
 * sync_ratelimit remains as before.

Further changes:
----------------
Performed s@sysctl_dccp_feat@sysctl_dccp@g since the sysctls are now in feat.c.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>

1 files changed, 8 insertions, 3 deletions

diff --git a/net/dccp/feat.c b/net/dccp/feat.c
index 843465999854..4c95cbdb0e01 100644
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -26,6 +26,11 @@
 #include "ccid.h"
 #include "feat.h"
 
+/* feature-specific sysctls - initialised to the defaults from RFC 4340, 6.4 */
+unsigned long   sysctl_dccp_sequence_window __read_mostly = 100;
+int             sysctl_dccp_rx_ccid         __read_mostly = 2,
+                sysctl_dccp_tx_ccid         __read_mostly = 2;
+
 /*
  * Feature activation handlers.
  *
@@ -1141,7 +1146,7 @@ int dccp_feat_init(struct sock *sk)
 
         /* Non-negotiable (NN) features */
         rc = __feat_register_nn(fn, DCCPF_SEQUENCE_WINDOW, 0,
-                                    sysctl_dccp_feat_sequence_window);
+                                    sysctl_dccp_sequence_window);
         if (rc)
                 return rc;
 
@@ -1172,8 +1177,8 @@ int dccp_feat_init(struct sock *sk)
         if (ccid_request_modules(tx.val, tx.len))
                 goto free_ccid_lists;
 
-        if (!dccp_feat_prefer(sysctl_dccp_feat_tx_ccid, tx.val, tx.len) ||
-            !dccp_feat_prefer(sysctl_dccp_feat_rx_ccid, rx.val, rx.len))
+        if (!dccp_feat_prefer(sysctl_dccp_tx_ccid, tx.val, tx.len) ||
+            !dccp_feat_prefer(sysctl_dccp_rx_ccid, rx.val, rx.len))
                 goto free_ccid_lists;
 
         rc = __feat_register_sp(fn, DCCPF_CCID, true, false, tx.val, tx.len);