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86739fb96e
This fixes a problem caused by the overlap of the connection-setup and established-state phases of DCCP connections. During connection setup, the client retransmits Confirm Feature-Negotiation options until a response from the server signals that it can move from the half-established PARTOPEN into the OPEN state, whereupon the connection is fully established on both ends (RFC 4340, 8.1.5). However, since the client may already send data while it is in the PARTOPEN state, consequences arise for the Maximum Packet Size: the problem is that the initial option overhead is much higher than for the subsequent established phase, as it involves potentially many variable-length list-type options (server-priority options, RFC 4340, 6.4). Applying the standard MPS is insufficient here: especially with larger payloads this can lead to annoying, counter-intuitive EMSGSIZE errors. On the other hand, reducing the MPS available for the established phase by the added initial overhead is highly wasteful and inefficient. The solution chosen therefore is a two-phase strategy: If the payload length of the DataAck in PARTOPEN is too large, an Ack is sent to carry the options, and the feature-negotiation list is then flushed. This means that the server gets two Acks for one Response. If both Acks get lost, it is probably better to restart the connection anyway and devising yet another special-case does not seem worth the extra complexity. The result is a higher utilisation of the available packet space for the data transmission phase (established state) of a connection. The patch (over-)estimates the initial overhead to be 32*4 bytes -- commonly seen values were around 90 bytes for initial feature-negotiation options. It uses sizeof(u32) to mean "aligned units of 4 bytes". For consistency, another use of 4-byte alignment is adapted. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| .. | ||
| ccids | ||
| ackvec.c | ||
| ackvec.h | ||
| ccid.c | ||
| ccid.h | ||
| dccp.h | ||
| diag.c | ||
| feat.c | ||
| feat.h | ||
| input.c | ||
| ipv4.c | ||
| ipv6.c | ||
| ipv6.h | ||
| Kconfig | ||
| Makefile | ||
| minisocks.c | ||
| options.c | ||
| output.c | ||
| probe.c | ||
| proto.c | ||
| sysctl.c | ||
| timer.c | ||