Why TCP_MAX_SACK == 3 ?

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On Tue, 8 Mar 2005, Noritoshi Demizu wrote:

> In netinet/tcp.h, TCP_MAX_SACK is defined as follows.
>
> #define	TCP_MAX_SACK	3	/* MAX # SACKs sent in any segment */
>
> Shouldn't it be 4?  If a peer node does not use TCP timestamps option,
> four SACK blocks can be sent.  For example, if my memory serves correctly,
> Microsoft Windows does not use TCP timestamps option by default.
>
>
> By the way, currently, both window scale option and timestamps option
> are controled by one sysctl variable: net.inet.tcp.rfc1323.
> Wouldn't it be nice if each option had its own sysctl variable?
>
> Regards,
> Noritoshi Demizu

As Im showing in my source tree for 4.11 \
#define TCPOPT_SACK_PERMITTED   4               /* Experimental */
#define    TCPOLEN_SACK_PERMITTED       2
#define TCPOPT_SACK             5               /* Experimental */
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