CRIU-RPC is a remote procedure call (RPC) protocol which uses Google Protocol Buffers to encode its calls. The requests are served by CRIU service launched with criu service command. It uses a SEQPACKET Unix domain socket listening at /var/run/criu-service.socket as a transport.
The criu_req/criu_resp are two main messages 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. See the API compliance page for information what each option might mean.
Request
This is the header of the request. It defines the operation requested and options.
message criu_req {
required criu_req_type type = 1;
optional criu_opts opts = 2;
}
There are 8 request/response types for now.
enum criu_req_type {
EMPTY = 0;
DUMP = 1; /* criu dump */
RESTORE = 2; /* criu restore */
CHECK = 3; /* criu check */
PRE_DUMP = 4; /* criu pre-dump */
PAGE_SERVER = 5; /* criu page-server */
CPUINFO_DUMP = 7; /* criu cpuinfo dump */
CPUINFO_CHECK = 8; /* criu cpuinfo check */
}
message criu_opts {
required int32 images_dir_fd = 1;
optional int32 pid = 2; /* if not set on dump, will dump requesting process */
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];
optional string log_file = 10; /* No subdirs are allowed. Consider using work-dir */
optional criu_page_server_info ps = 11;
optional bool notify_scripts = 12;
optional string root = 13;
optional string parent_img = 14;
optional bool track_mem = 15;
optional bool auto_dedup = 16;
optional int32 work_dir_fd = 17;
optional bool link_remap = 18;
repeated criu_veth_pair veths = 19;
optional uint32 cpu_cap = 20 [default = 0xffffffff];
optional bool force_irmap = 21;
repeated string exec_cmd = 22;
repeated ext_mount_map ext_mnt = 23;
optional bool manage_cgroups = 24;
repeated cgroup_root cg_root = 25;
optional bool rst_sibling = 26; /* swrk only */
}
Comments and examples
- If no pid is set and type is DUMP, CRIU will dump client process by default.
- All processes in the subtree starting with <pid> must have the same uid, as a client, or client's uid must be root (uid == 0), otherwise CRIU will return error.
- Only the images_dir_fd is required, all other fields are optional. Client must open directory for/with images by himself and set images_dir_fd to it's fd. CRIU will open /proc/<client's_pid>/fd/<images_dir_fd>.
The logic of setting request is the same as when setting options in console. Here is an example:
#criu restore -D /path/to/imgs_dir -v4 -o restore.log
is equal to:
request.type = RESTORE;
request.opts.imgs_dir_fd = open("/path/to/imgs_dir")
request.opts.log_level = 4
request.opts.log_file = "restore.log"
Sub-messages for options
- Info about page-server.
message criu_page_server_info {
optional string address = 1; /* bind address -- if not set 0.0.0.0 is used */
optional int32 port = 2; /* bind port -- if not set on request, autobind is used and port is returned in response */
optional int32 pid = 3; /* page-server pid -- returned in response */
optional int32 fd = 4; /* could be used to inherit fd by page-server */
}
- If port is 0 server will auto-bind and the port will be returned back in responce.
message criu_veth_pair {
required string if_in = 1; /* inside veth device name */
required string if_out = 2; /* outside veth device name */
};
- Info about veth mappings (--ext-mount-map analogue)
message ext_mount_map {
required string key = 1;
required string val = 2;
};
- Specifying where cgroup root should be (--cgroup-root analogue)
message cgroup_root {
optional string ctrl = 1;
required string path = 2;
};
Response
This message is sent after (un)successful execution of the request.
message criu_resp {
required criu_req_type type = 1;
required bool success = 2;
optional criu_dump_resp dump = 3;
optional criu_restore_resp restore = 4;
optional criu_notify notify = 5;
optional criu_page_server_info ps = 6;
}
Field "success" reports result of processing request, while criu_***_resp store some request-specific information. The response type is set to the corresponding request type or to EMPTY to report a "generic" error.
- The criu_dump_resp is used to store response from DUMP request.
message criu_dump_resp {
optional bool restored = 1;
}
This message can be sent twice -- one for the process that calls DUMP and the other for the same process again if it requested a self-dump. In the latter case the restored field would be true.
- The response on RESTORE request.
message criu_restore_resp {
required int32 pid = 1;
}
Field "pid" is set to the PID of the newly restored process.
Notifications
--action-script analog.
message criu_notify {
optional string script = 1;
optional int32 pid = 2;
}
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 with set request-specific criu_***_resp field back. If CRIU gets unknown type of request, it will return criu_resp with type == EMPTY and success == false.
To launch service server, run:
#criu service [options]
Options accepted by service are
- --address <path>
- is where to put listening socket
- --pid-file <path>
- is where to write pid of service process
- --daemon
- tells service to daemonize
- -o <file>
- says where to write logs
- -v[N]
- sets the log-level
systemd
If you are running systemd you can make service start and operate automatically. First do
make install
to make files criu.service and criu.socket appear in systemd configs (/lib/systemd/system/). Then
systemctl start criu.socket
to get /var/run/criu-service.socket, and
systemctl enable criu.socket
to make /var/run/criu-service.socket available at boot.
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.
There's a library that implements simple wrappers on top of RPC.