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This explains the meaning of '''external socket is used''' error message, and the purpose of '''<code>--ext-unix-sk</code>''' option.

This explains the meaning of '''external socket is used''' error message, and the purpose of '''<code>--external unix[...]</code>''' option.

== Error meaning ==

== Error meaning ==

However, sometimes it is possible to dump and successfully restore only one end of a unix socket pair. One particular example is the datagram sockets with on-way connection (client to server) used e.g. by <code>logd</code>. Server opens a datagram socket and waits on it for messages to be written into a log file. Processes using logd also create datagram sockets and connect those to the server. These connections are thus uni-directional. In this case it is possible to dump a program with the client-side socket and on restore the socket needs to be reconnected back to the original server.

However, sometimes it is possible to dump and successfully restore only one end of a unix socket pair. One particular example is the datagram sockets with on-way connection (client to server) used e.g. by <code>logd</code>. Server opens a datagram socket and waits on it for messages to be written into a log file. Processes using logd also create datagram sockets and connect those to the server. These connections are thus uni-directional. In this case it is possible to dump a program with the client-side socket and on restore the socket needs to be reconnected back to the original server.

This is when <code>--ext-unix-sk</code> option should be used. By providing this option (for both dump and restore commands), user states "I know there may be uni-directional dgram unix connections, and I will make sure the server end will exist on restore".

This is when {{Opt|--external}} option should be used. By providing this option for both dump (now) and restore (in plans) commands, user states "I know there may be uni-directional dgram unix connections, and I will make sure the server end will exist on restore".

For '''criu dump''', this option enables dumping ''datagram'' unix sockets with additional information about that other ("external") socket it is connected to.

For '''criu dump''', this option enables dumping ''datagram'' unix sockets with additional information about that other ("external") socket it is connected to.

the other one will see EOF on the socket and may close it.

the other one will see EOF on the socket and may close it.

The plan for this is to extend the <code>--ext-unix-sk</code> semantics to work like this:

The plan for this is to extend the <code>--external unix[...]</code> semantics to work like this:

* On dump, the <code>--ext-unix-sk $id</code> says that socket with $id is OK to be disconnected

* On dump, the <code>--external unix[id]</code> says that socket with <code>''id''</code> is OK to be disconnected

* On restore, the <code>--ext-unix-sk$id[=$path]</code> says that the socket $id should be reconnected back to the path it say on dump (or to the $path).

* On restore, the <code>--external unix[''id'']:''path''</code> says that the socket <code>''id''</code> should be reconnected back to the path it say on dump (or to the specified <code>''path''</code>) (THIS IS IN PLANS!)

=== socketpair ===

=== socketpair ===

Unnamed unix sockets created with <code>socketpair()</code> system call can be dumped and restored.

Unnamed unix sockets created with <code>socketpair()</code> system call can be dumped and restored.

On dump, put inode of this socket in <code>--ext-unix-sk</code> option, for example:

On dump, tell inode of this socket to CRIU, like this

  criu dump -D images -o dump.log -v4 --ext-unix-sk=11890815 -t 16528

  criu dump -D images -o dump.log -v4 --external unix[11890815] -t 16528

On restore, the server should create a new pair and call <code>criu restore</code> asking it to [[Inheriting FDs on restore|inherit]] one.

On restore, the server should create a new pair and call <code>criu restore</code> asking it to [[Inheriting FDs on restore|inherit]] one.

Test is available for this feature, see test/socketpairs in criu sources.

Test is available for this feature, see test/socketpairs in criu sources.

== See also ==

== See also ==

[[Category:HOWTO]]

[[Category:HOWTO]]

[[Category:API]]

[[Category:API]]

[[Category:External]]

[[Category:External]]