CRIU-RPC is a remote procedure call (RPC) protocol which uses Google Protocol Buffers to encode its calls and SOCK_SEQPACKET Unix domain socket as a transport mechanism.
Protobuf messages
criu_req/criu_resp -- wrappers for requests/responses. They are to be used for transferring messages and needed to provide compatibility with an older versions of rpc. Field type in them _must_ be set accordingly to type of request/response that is stored. Types of request/response are defined in enum criu_req_type.
Request
criu_req
message criu_req {
required criu_req_type type = 1;
optional criu_dump_req dump = 2;
}
criu_req_type
There is only 1 request/response type for now.
enum criu_req_type {
EMPTY = 0;
DUMP = 1;
}
criu_dump_req
It is used to store dump options.
message criu_dump_req {
required int32 images_dir_fd = 1;
optional int32 pid = 2;
optional bool leave_running = 3;
optional bool ext_unix_sk = 4;
optional bool tcp_established = 5;
optional bool evasive_devices = 6;
optional bool shell_job = 7;
optional bool file_locks = 8;
optional int32 log_level = 9 [default = 2];
}
If no pid is set, CRIU will dump client process by default. Note: Whole tree <pid> must have the same uid, as a client, or client's uid must be == 0, otherwise CRIU won't dump nothing at all.
Only images_dir_fd is required, all other fields may not be set. Client must open directory for images by himself and set images_dir_fd to it's fd. CRIU will open /proc/<client's_pid>/fd/<images_dir_fd>, so it will work, if client is in another namespace.
For other options description, please run "criu -h".
Response
criu_resp
message criu_resp {
required criu_req_type type = 1;
required bool success = 2;
optional criu_dump_resp dump = 3;
}
criu_dump_resp
criu_dump_resp is used to store response from CRIU.
message criu_dump_resp {
optional bool restored = 1;
}
Field "restored" is set to "true" if process was restored.
Run
Server
On a server side, CRIU creates SOCK_SEQPACKET Unix socket and listens for connections on it. After receiving criu_req, CRIU processes it, do what is requested and sends criu_resp back.
To launch service server run:
#criu service --address <socket_address>
If no address is set, "/tmp/criu_service.socket" is used by default. You may also like to demonize server(-d), set log level(-v<N>) or set log file(-o <logname>). For the full list of options, please run "criu -h".
Client
Client, in its turn, must connect to service socket, send criu_req with request in it, and wait for a criu_resp with response. You can find examples of client programs in C and Python in test/rpc/.
With RPC facilities one can perform a self dump.