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→Timestamp
== Timestamp ==
== Timestamp ==
"The sender's timestamp clock is used as a source of monotonic non-decreasing values to stamp the segments"(rfc7323). The Linux kernel uses the jiffies counter as the tcp timestamp.
"The sender's timestamp clock is used as a source of monotonic non-decreasing values to stamp the segments"(rfc7323). The Linux kernel uses the jiffies counter as the tcp timestamp.
We add the TCP_TIMESTAMP options to be able to compensate a difference between jiffies counters, when a connection is migrated on another host. When a connection is dumped, criu calls getsockopt(TCP_TIMESTAMP) to get a current timestamp, then on restore it calls setsockopt(TCP_TIMESTAMP) to set this timestamp as a starting point.
<code>#define tcp_time_stamp ((__u32)(jiffies))</code>
We add the <code>TCP_TIMESTAMP</code> options to be able to compensate a difference between jiffies counters, when a connection is migrated on another host. When a connection is dumped, criu calls <code>getsockopt(TCP_TIMESTAMP)</code> to get a current timestamp, then on restore it calls <code>setsockopt(TCP_TIMESTAMP)</code> to set this timestamp as a starting point.
== Checkpoint and restore TCP connection ==
== Checkpoint and restore TCP connection ==