Criu

This module contains some convenience functions and types for building requests to, and actually calling, the Checkpoint/Restore In Userspace (criu) RPC API - see https://criu.org/RPC.

Request

The simplest example of a call to CRIU is a check request. For convenience this module re-exports some libraries used for building Criu_reqs.

To build a check request:

> let checkRequest = build  (type' .~ CHECK)  :: Criu_req
Criu_req {
  _Criu_req'type' = CHECK
  , _Criu_req'opts = Nothing
  , _Criu_req'notifySuccess = Nothing
  , _Criu_req'keepOpen = Nothing
  , _Criu_req'features = Nothing
  }

checkRequest is also a function exposed in this module. To send that request:

> let checkRequest = build  (type' .~ CHECK)  :: Criu_req
> callCriu "/var/tmp/criu_service.socket" checkRequest
Right (
  Criu_resp
    { _Criu_resp'type' = CHECK
    , _Criu_resp'success = True
    , _Criu_resp'dump = Nothing
    , _Criu_resp'restore = Nothing
    , _Criu_resp'notify = Nothing
    , _Criu_resp'ps = Nothing
    , _Criu_resp'crErrno = Nothing
    , _Criu_resp'features = Nothing
    , _Criu_resp'crErrmsg = Nothing
    }
)

callCriu may throw an IOException, to wrap these, specifically, in Either use callCriu' instead.

callCriu :: FilePath -> Criu_req -> IO (Either String Criu_resp)

Send request to a criu service. Takes a filepath to the criu service socket and a criu request. Returns an Either of the response or a String representing an error if there is an issue decoding the response from the criu service.

callCriu' :: FilePath -> Criu_req -> IO (Either String Criu_resp)

Send a request to a criu service, but wraps up IOExceptions in an Either.

Request Builders

To build Criu_req's you will need .~ from Lens.Family2, build from Data.ProtoLens and of course the lenses and types from Proto.Criu.Rpc.

Above we saw a simple check request, the next example is a dump request. This one is a bit more complex. Criu requires the file descriptor of an open directory when issuing a dump request to it. This is the directory where it will dump the process tree and all necessary information about the process. Below we set the pid to 11612 and we also set shellJob to True, which tells criu that the process we want to dump is running in a shell.

> fd <- getDirFdAsInt "/var/tmp/dump"
> let dumpReqOpts = build ((imagesDirFd .~ fd) . (pid .~ 11612) . (shellJob .~ True)) :: Criu_opts
> let dumpRequest = build ((type' .~ DUMP) . (opts .~ dumpReqOpts)) :: Criu_req
> callCriu' "/var/tmp/criu_service.socket" dumpRequest
Right (
  Criu_resp {
    _Criu_resp'type' = DUMP
    , _Criu_resp'success = True
    , _Criu_resp'dump = Just (
      Criu_dump_resp {
        _Criu_dump_resp'restored = Just False
      }
    ), _Criu_resp'restore = Nothing
    , _Criu_resp'notify = Nothing
    , _Criu_resp'ps = Nothing
    , _Criu_resp'crErrno = Nothing
    , _Criu_resp'features = Nothing
    , _Criu_resp'crErrmsg = Nothing
    })

checkRequest :: Criu_req

Builds a check request.

dumpRequest :: Criu_opts -> Criu_req

Builds a dump request from the give Criu_opts.

dumpRequestOpts :: Fd -> Int32 -> Criu_opts

Builds a minimal dump based Criu_opts from a file descriptor pointing to the location of the open directory you wish to dump the process tree and the pid of the process tree you wish to dump. Note that really the only requirement is to set imagesDirFd, not setting the pid will dump the calling process, this is not something that seems likely when using this client.

openDir :: FilePath -> IO Fd

Open a directory, returning its file descriptor. Caution - make sure to close the file descriptor! Can use closeDirFd.

closeDirFd :: Fd -> IO ()

A convenience method, can be used to close the FD returned by openDir. This is literally just System.Posix.IO's closeFd.