The new sysctl and socket option added for PLPMTUD (RFC8899)

[Xin Long <lucien.xin@gmail.com>]

Hi, Michael,

In the linux implementation of RFC8899, we decided to introduce one
sysctl and one socket option for users to set up the PLPMUTD probe:

1. sysctl -w net.sctp.plpmtud_probe_interval=1

plpmtud_probe_interval - INTEGER
        The interval (in milliseconds) between PLPMTUD probe chunks. These
        chunks are sent at the specified interval with a variable size to
        probe the mtu of a given path between 2 associations. PLPMTUD will
        be disabled when 0 is set.

        Default: 0

2. a socket option that can be used per socket, assoc or transport

/* PLPMTUD Probe Interval socket option */
struct sctp_probeinterval {
        sctp_assoc_t spi_assoc_id;
        struct sockaddr_storage spi_address;
        __u32 spi_interval;
};

#define SCTP_PLPMTUD_PROBE_INTERVAL    133


The value above will enable/disable the PLPMUTD probe by setting up the probe
interval for the timer. When it's 0, the timer will also stop and
PLPMUTD is disabled.
By this way, we don't need to introduce more options.

We're expecting to keep consistent with BSD on this, pls check and
share your thoughts.

Thanks.