Changes

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>,

netfilter rule is configured that drops all the packets from peer to a socket we're dealing with. This rule sits

netfilter rule is configured that drops all the packets from peer to a socket we're dealing with. This rule sits

in the host netfilter tables after the criu dump command finishes and it should be there when you issue the

in the host netfilter tables after the criu dump command finishes and it should be there when you issue the

criu restore one.

criu restore one. The locking method can be specified using the {{opt|--network-lock}} option.

Another thing to note is -- on restore there should be available the IP address, that was used by the connection.

Another thing to note is -- on restore there should be available the IP address, that was used by the connection.

IP address should be copied too.

IP address should be copied too.

That said, the command line option <code>--tcp-established</code> should be used when calling criu to explicitly state, that the

That said, the command line option {{opt|--tcp-established}} should be used when calling criu to explicitly state, that the

caller is aware of this "transitional" state of the netfilter.

caller is aware of this "transitional" state of the netfilter.

== States ==

== States ==

=== TCP_SYN_SENT ===

=== 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>conenct()</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.

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 ===

=== Half-closed sockets ===