1,067
edits
Changes
Lots of English, formatting fixes etc
CRIU-RPC is a remote procedure call (RPC) protocol which uses Google Protocol Buffers to encode its calls. The requests are served by CRIU when either launched in so called "swrk" mode or by service started with the <code>criu service</code> command. It uses a SEQPACKET Unix domain socket for transport. In case of standalone service it listens at <code>/var/run/criu-service.socket</code> as a transport.
CRIU-RPC is a remote procedure call (RPC) protocol which uses Google Protocol Buffers to encode its calls. The requests are served by CRIU when either launched in so called "swrk" mode or by a service started with the <code>criu service</code> command. It uses a <code>SEQPACKET</code> Unix domain socket for transport. In case of a standalone service it listens at <code>/var/run/criu-service.socket</code> 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.
The <code>criu_req</code>/<code>criu_resp</code> 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 <code>enum criu_req_type</code>. See the [[API compliance]] page for information what each option might mean.
== Protocol ==
== Protocol ==
The protocol is simple -- client sends a ''criu_req'' message to server, server responds back with ''criu_resp''. In most of the cases the socket gets closed, but there are three exceptions from this rule, see below.
The protocol is simple: client sends a <code>criu_req</code> message to server, server responds back with <code>criu_resp</code>. In most of the cases the socket gets closed, but there are three exceptions from this rule, see below.
== Request ==
== Request ==
This is the header of the request. It defines the operation requested and options.
This is the header of the request. It defines the operation requested and options.
<pre>
<source lang="c">
message criu_req {
message criu_req {
required criu_req_type type = 1;
required criu_req_type type = 1;
optional keep_open = 4; /* for multi-req, below */
optional keep_open = 4; /* for multi-req, below */
}
}
</pre>
</source>
Currently, there are a few request/response types:
<pre>enum criu_req_type {
<source lang="c">
enum criu_req_type {
EMPTY = 0;
EMPTY = 0;
DUMP = 1; /* criu dump */
DUMP = 1; /* criu dump */
CPUINFO_CHECK = 8; /* criu cpuinfo check */
CPUINFO_CHECK = 8; /* criu cpuinfo check */
}
}
</pre>
</source>
<pre>message criu_opts {
The following options are available:
<source lang="c">
message criu_opts {
required int32 images_dir_fd = 1;
required int32 images_dir_fd = 1;
optional int32 pid = 2; /* if not set on dump, will dump requesting process */
optional int32 pid = 2; /* if not set on dump, will dump requesting process */
optional bool rst_sibling = 26; /* swrk only */
optional bool rst_sibling = 26; /* swrk only */
}
}
</pre>
</source>
=== Comments and examples ===
=== Comments and examples ===
* If no pid is set and type is DUMP, CRIU will dump client process by default.
* If no <code>pid</code> is set and type is <code>DUMP</code>, 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.
* All processes in the subtree starting with <code>''pid''</code> must have the same uid, as a client, or client's uid must be root (uid == 0), otherwise CRIU will return an 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>.
* Only the <code>images_dir_fd</code> is required, all other fields are optional. Client must open directory for/with images by itself and set <code>images_dir_fd</code> to the opened <code>fd</code>. CRIU will open <code>/proc/''client_pid''/fd/''images_dir_fd''</code>.
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
This is equal to:
is equal to:
<source lang="c">
<pre>
request.type = RESTORE;
request.type = RESTORE;
request.opts.log_level = 4
request.opts.log_level = 4
request.opts.log_file = "restore.log"
request.opts.log_file = "restore.log"
</pre>
</source>
=== Sub-messages for options ===
=== Sub-messages for options ===
<pre>
==== Info about page-server ====
<source lang="c">
message criu_page_server_info {
message criu_page_server_info {
optional string address = 1; /* bind address -- if not set 0.0.0.0 is used */
optional string address = 1; /* bind address -- if not set 0.0.0.0 is used */
optional int32 fd = 4; /* could be used to inherit fd by page-server */
optional int32 fd = 4; /* could be used to inherit fd by page-server */
}
}
</pre>
</source>
<pre>
<source lang="c">
message criu_veth_pair {
message criu_veth_pair {
required string if_in = 1; /* inside veth device name */
required string if_in = 1; /* inside veth device name */
required string if_out = 2; /* outside veth device name */
required string if_out = 2; /* outside veth device name */
};
};
</pre>
</source>
==== Info about veth mappings (<code>--ext-mount-map</code> analogue) ====
<pre>
<source lang="c">
message ext_mount_map {
message ext_mount_map {
required string key = 1;
required string key = 1;
required string val = 2;
required string val = 2;
};
};
</pre>
</source>
==== Specifying where cgroup root should be (<code>--cgroup-root</code> analogue) ====
<pre>
<source lang="c">
message cgroup_root {
message cgroup_root {
optional string ctrl = 1;
optional string ctrl = 1;
required string path = 2;
required string path = 2;
};
};
</pre>
</source>
== Response ==
== Response ==
This message is sent after (un)successful execution of the request.
This message is sent after (un)successful execution of the request.
<pre>
<source lang="c">
message criu_resp {
message criu_resp {
required criu_req_type type = 1;
required criu_req_type type = 1;
optional int32 cr_errno = 7;
optional int32 cr_errno = 7;
}
}
</pre>
</source>
The field <code>success</code> reports result of processing request, while <code>criu_***_resp</code> store some request-specific information. The response type is set to the corresponding request type or to <code>EMPTY</code> to report a "generic" error. If <code>success == false</code>, one should check <code>cr_errno</code> field to get a more detailed error code (see [https://github.com/xemul/criu/blob/master/include/cr-errno.h#L8 include/cr-errno.h]).
==== The criu_dump_resp is used to store response from DUMP request ====
<source lang="c">
<pre>
message criu_dump_resp {
message criu_dump_resp {
optional bool restored = 1;
optional bool restored = 1;
}
}
</pre>
</source>
This message can be sent twice — one time for the process that calls DUMP, and another time for the same process again, in case it requested a self-dump. In the latter case the ''restored'' field would be true.
==== The response on RESTORE request ====
<source lang="c">
<pre>
message criu_restore_resp {
message criu_restore_resp {
required int32 pid = 1;
required int32 pid = 1;
}
}
</pre>
</source>
The <code>pid</code> field is set to the PID of the newly restored process.
The ''criu_page_server_info'' from requests will be sent back on PAGE_SERVER request. The ''port'' field will contain the port to which server is bound.
==== Info about page server ====
The <code>criu_page_server_info</code> from requests will be sent back on <code>PAGE_SERVER</code> request. The <code>port</code> field will contain the port to which the server is bound.
=== Notifications ===
=== Notifications ===
<pre>
If the <code>opts.notify_scripts</code> in the request is set to <code>TRUE</code>, CRIU would report back resp messages with type set to <code>NOTIFY</code> and this field present. The notifications are the way [[action scripts]] work for RPC mode.
<source lang="c">
message criu_notify {
message criu_notify {
optional string script = 1;
optional string script = 1;
optional int32 pid = 2;
optional int32 pid = 2;
}
}
</pre>
</source>
After handling the notification the client must response with the request again with the type set to NOTIFY and the ''notify_success'' set to the successfulness of the notification. In case of successful notification acknowledge the server doesn't close the socket and continues to work.
After handling the notification the client must response with the request again with the type set to <code>NOTIFY</code> and the <code>notify_success</code> set to the whether the notification was successful. In case of successful notification acknowledge the server doesn't close the socket and continues to work.
== Pre-dumps ==
== Pre-dumps ==
Before issuing a DUMP request client may send one or more PRE_DUMP requests. Once the PRE_DUMP is sent and response is received, client may send one more PRE_DUMP or DUMP request. The server would only close the socket after the DUMP one.
Before issuing a <code>DUMP</code> request client may send one or more <code>PRE_DUMP</code> requests. Once the <code>PRE_DUMP</code> is sent and response is received, client may send one more <code>PRE_DUMP</code> or <code>DUMP</code> request. The server would only close the socket after the <code>DUMP</code> one.
== Multi-request mode ==
== Multi-request mode ==
If the ''req.keep_open'' flag is set to true server will not close the socket after response, but will wait for more requests. This mode is supported only for the following request types:
If the <code>req.keep_open</code> flag is set to true server will not close the socket after response, but will wait for more requests. This mode is supported only for the following request types:
* PRE_DUMP (automatically)
* <code>PRE_DUMP</code> (automatically)
* PAGE_SERVER
* <code>PAGE_SERVER</code>
* CPUINFO_DUMP and CPUINFO_CHECK
* <code>CPUINFO_DUMP</code> and <code>CPUINFO_CHECK</code>
== Run ==
== Run ==
=== SWRK mode ===
=== SWRK mode ===
This mode turns on when one <code>fork() + exec()</code> CRIU with the <code>swrk</code> action and one more argument specifying the number of descriptor with ''seqpacket'' unix socket. With this CRIU works as service worker task accepting standard RPC requests via the mentioned socket and using one to do action scripts notifications and result reporting.
This mode turns on when one <code>fork() + exec()</code> CRIU with the <code>swrk</code> action and one more argument specifying the number of descriptor with <code>SOCK_SEQPACKET</code> Unix socket. With this CRIU works as service worker task accepting standard RPC requests via the mentioned socket and using one to do action scripts notifications and result reporting.
=== Server ===
=== Server ===
To launch service server, run:
On a server side, CRIU creates <code>SOCK_SEQPACKET</code> Unix socket and listens for connections on it. After receiving <code>criu_req</code>, CRIU processes it, does what was requested and sends <code>criu_resp</code> with set request-specific <code>criu_***_resp</code> field back.
If CRIU gets unknown type of request, it will return <code>criu_resp</code> with <code>type == EMPTY</code> and <code>success == false</code>.
To launch the service, run:
# criu service [options]
Options accepted by service are
Options accepted by service are
; --address <path>
; --address <path>
: is where to put listening socket
: where to put listening socket
; --pid-file <path>
; --pid-file <path>
: is where to write pid of service process
: where to write pid of service process
; --daemon
; --daemon
; -v[N]
; -v[N]
: sets the log-level
: sets the log level
==== systemd ====
If you are running systemd, you can make service start and operate automatically. First do
If you are running systemd you can make service start and operate automatically. First do
<pre>
make install
systemctl start criu.socket
to make files <code>criu.service</code> and <code>criu.socket</code> appear in systemd configs (<code>/lib/systemd/system/</code>).
Then run
systemctl start criu.socket
to get /var/run/criu-service.socket, and
to get /var/run/criu-service.socket, and
to make /var/run/criu-service.socket available at boot.
systemctl enable criu.socket
to make <code>/var/run/criu-service.socket</code> available at boot.
=== Client ===
=== 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.
Client, in its turn, must connect to service socket, send <code>criu_req</code> with request in it, and wait for a <code>criu_resp</code> with response.
You can find examples of client programs in C and Python in test/rpc/.
You can find examples of client programs in C and Python in test/rpc/.
With RPC facilities one can perform a [[self dump]].
With RPC facilities one can perform a [[self dump]].
There's a [[C_API|library]] that implements simple wrappers on top of RPC.
There's a [[C API|library]] that implements simple wrappers on top of RPC.
== See also ==
* [[C API]]
[[Category: API]]
[[Category: API]]