Libsoccr

Libsoccr is the library that does TCP connection checkpoint and restore. It sits in criu sources and includes an API header and a static library.

Overview

To checkpoint a TCP connection one should

1. pause a socket (referenced by descriptor)
2. get socket data
3. get contents of two queues
4. (optionally) resume the socket
5. close it

To restore a connection one should

1. create a socket
2. pause one
3. restore unbound data
4. bind() and/or connect() socket to whatever addresses is appropriate using standard calls
5. restore noq data
6. put contents of two queues
7. restore remaining data

Data types

In soccr/soccr.h there are three types declares

struct libsoccr_sk

It's an abstract handler returned by pausing routine that is used as an opaque identifier by the rest of the libsoccr calls

struct libsoccr_sk_data

A structure containing a set of 32-bit values that are returned by getter and that are to be passed as is to the setter call

struct libsoccr_addr

A structure that defines soccaddr for a socket. It's used by set/get calls described further.

Data internals

Inside the libsoccr_sk_data structure there's a special field called flags that gives information about the meaning of some other fields. Though it's not bad just to pass this structure as-is between libsoccr calls, doing some optimization based on flags is OK.

So here are the flags that make sense

SOCCR_FLAGS_WINDOW == 0x1

When set indicates, that fields snd_wl1, snd_wnd, max_window, rcv_wnd and rcv_wup contain some valuable data (0 is valid value for any)

Calls

Generic

struct libsoccr_sk *libsoccr_pause(int sk)

Pauses the socket and returns a handler for further operations. Any data flow for this socket must be blocked by the caller before this call.

void libsoccr_resume(struct libsoccr_sk *)

Resumes the socket. Data flow unlock may happen before this.

void libsoccr_set_log(unsigned int level, void (*fn)(unsigned int level, const char *fmt, ...))

Sets a function that will be called when libsoccr will want to print something on the screen.

Dump

int libsoccr_get_sk_data(struct libsoccr_sk *sk, struct libsoccr_sk_data *data, unsigned data_size)

Fills in the data structure with the info get from paused socket. The data_size should be the size of the structure passed. The return code is the size of the structure really filled with data.

char *libsoccr_get_queue_bytes(struct libsoccr_sk *sk, int queue_id, int steal)

Returns a malloc()-ed array with the contents of the queue. The queue can be TCP_RECV_QUEUE or TCP_SEND_QUEUE. The amount of bytes in each is data.inq_len and data.outq_len respectively. The steal is a boolean value specifying whether the caller would free() the buffers himself (1) or expects the _resume() to do it (0).

Restore

int libsoccr_set_sk_data_unbound(struct libsoccr_sk *sk, struct libsoccr_sk_data *data, unsigned data_size)

Restores data on a socket from the data structure. Should be called before bind()-ing or connect()-ing the socket.

int libsoccr_set_sk_data_noq(struct libsoccr_sk *sk, struct libsoccr_sk_data *data, unsigned data_size)

Continues restoration after bind() and/or connect(), but before the queue data restore (see below)

int libsoccr_set_sk_data(struct libsoccr_sk *sk, struct libsoccr_sk_data *data, unsigned data_size)

Completes the restoration after queues, but doesn't resume the socket.

int libsoccr_set_queue_bytes(struct libsoccr_sk *sk, struct libsoccr_sk_data *data, unsigned data_size, int queue, char *buf)

Puts back the contents of the respective queue.