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| The <code>TCP_REPAIR</code> socket option was added to the kernel 3.5 to help with C/R for TCP sockets. | | The <code>TCP_REPAIR</code> socket option was added to the kernel 3.5 to help with C/R for TCP sockets. |
| | | |
− | When this option is used, a socket is switched into a special mode, in which any action performed on it | + | When this option is used, the socket is switched into a special mode, in which any action performed on it |
| does not result in anything defined by an appropriate protocol actions, but rather directly puts the socket | | does not result in anything defined by an appropriate protocol actions, but rather directly puts the socket |
− | into a state, in which the socket is expected to be at the end of the successfully finished operation. | + | into the state that the socket is expected to be in at the end of a successfully finished operation. |
| | | |
| For example, calling <code>connect()</code> on a repaired socket just changes its state to <code>ESTABLISHED</code>, | | For example, calling <code>connect()</code> on a repaired socket just changes its state to <code>ESTABLISHED</code>, |
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| All four can be read with <code>getsockopt()</code> calls to a socket and in order to restore them the <code>TCP_REPAIR_OPTIONS</code> sockoption is introduced. | | All four can be read with <code>getsockopt()</code> calls to a socket and in order to restore them the <code>TCP_REPAIR_OPTIONS</code> sockoption is introduced. |
| + | |
| + | == 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. |
| + | |
| + | <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 == |
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| could isolate the whole netns from network. Typically this is done by downing the respective veth pair end. | | could isolate the whole netns from network. Typically this is done by downing the respective veth pair end. |
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− | == More info == | + | == States == |
| + | === TCP_SYN_SENT === |
| + | There is only one difference with TCP_ESTABLISHED, we have to restore a socket and disable the repair mode before calling <code>connect()</code>. The kernel will send a one syn-sent packet with the same initial sequence number and sets the TCP_SYN_SENT state for the socket. |
| + | |
| + | === Half-closed sockets === |
| + | A socket is half-closed when it sent or received a fin packet. These sockets are in one for these states: TCP_FIN_WAIT1, TCP_FIN_WAIT2, TCP_CLOSING, TCP_LAST_ACL, TCP_CLOSE_WAIT. To restore these states, we restore a socket into the TCP_ESTABLISHED state and then we call shutfown(SHUT_WR), if a socket has sent a fin packet and we send a fake fin packet, if a socket has received it before. For example, if we want to restore the TCP_FIN_WAIT1 state, we have to call shutfown(SHUT_WR) and we can send a fake ack to the fin packet to restore the TCP_FIN_WAIT2 state. |
| + | |
| + | == See also == |
| + | * [[Simple TCP pair]] |
| + | * [[TCP repair TODO]] |
| + | * [[CLI/opt/--tcp-close|Dropping the connection]] |
| + | |
| + | == External links == |
| * http://lwn.net/Articles/495304/ | | * http://lwn.net/Articles/495304/ |
− | * [[TCP repair TODO]]
| |
| | | |
| [[Category:Under the hood]] | | [[Category:Under the hood]] |
− | [[Category:Network]]
| |
| [[Category:Sockets]] | | [[Category:Sockets]] |
| + | [[Category: Editor help needed]] |