[PATCH 05/19] c/r: documentation

[PATCH 05/19] c/r: documentation

[Dan Smith]

From: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>

Covers application checkpoint/restart, overall design, interfaces,
usage, shared objects, and and checkpoint image format.

Changelog[v19-rc1]:
  - Update documentation and examples for new syscalls API
  - [Liu Alexander] Fix typos
  - [Serge Hallyn] Update checkpoint image format
Changelog[v16]:
  - Update documentation
  - Unify into readme.txt and usage.txt
Changelog[v14]:
  - Discard the 'h.parent' field
  - New image format (shared objects appear before they are referenced
    unless they are compound)
Changelog[v8]:
  - Split into multiple files in Documentation/checkpoint/...
  - Extend documentation, fix typos and comments from feedback

Cc: linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org
Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
Signed-off-by: Dave Hansen <dave-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Acked-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Tested-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 Documentation/checkpoint/checkpoint.c      |   38 +++
 Documentation/checkpoint/readme.txt        |  370 ++++++++++++++++++++++++++++
 Documentation/checkpoint/self_checkpoint.c |   69 +++++
 Documentation/checkpoint/self_restart.c    |   40 +++
 Documentation/checkpoint/usage.txt         |  247 +++++++++++++++++++
 5 files changed, 764 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/checkpoint/checkpoint.c
 create mode 100644 Documentation/checkpoint/readme.txt
 create mode 100644 Documentation/checkpoint/self_checkpoint.c
 create mode 100644 Documentation/checkpoint/self_restart.c
 create mode 100644 Documentation/checkpoint/usage.txt

diff --git a/Documentation/checkpoint/checkpoint.c b/Documentation/checkpoint/checkpoint.c
new file mode 100644
index 0000000..8560f30
--- /dev/null
+++ b/Documentation/checkpoint/checkpoint.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+#include <linux/checkpoint.h>
+
+static inline int checkpoint(pid_t pid, int fd, unsigned long flags)
+{
+	return syscall(__NR_checkpoint, pid, fd, flags);
+}
+
+int main(int argc, char *argv[])
+{
+	pid_t pid;
+	int ret;
+
+	if (argc != 2) {
+		printf("usage: ckpt PID\n");
+		exit(1);
+	}
+
+	pid = atoi(argv[1]);
+	if (pid <= 0) {
+		printf("invalid pid\n");
+		exit(1);
+	}
+
+	ret = checkpoint(pid, STDOUT_FILENO, CHECKPOINT_SUBTREE);
+
+	if (ret < 0)
+		perror("checkpoint");
+	else
+		printf("checkpoint id %d\n", ret);
+
+	return (ret > 0 ? 0 : 1);
+}
diff --git a/Documentation/checkpoint/readme.txt b/Documentation/checkpoint/readme.txt
new file mode 100644
index 0000000..4fa5560
--- /dev/null
+++ b/Documentation/checkpoint/readme.txt
@@ -0,0 +1,370 @@
+
+	      Checkpoint-Restart support in the Linux kernel
+	==========================================================
+
+Copyright (C) 2008-2010 Oren Laadan
+
+Author:		Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
+
+License:	The GNU Free Documentation License, Version 1.2
+		(dual licensed under the GPL v2)
+
+Contributors:	Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
+		Serge Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
+		Dan Smith <danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
+		Matt Helsley <matthltc-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
+		Nathan Lynch <ntl-e+AXbWqSrlAAvxtiuMwx3w@public.gmane.org>
+		Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
+		Dave Hansen <dave-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
+
+
+Introduction
+============
+
+Application checkpoint/restart [C/R] is the ability to save the state
+of a running application so that it can later resume its execution
+from the time at which it was checkpointed. An application can be
+migrated by checkpointing it on one machine and restarting it on
+another. C/R can provide many potential benefits:
+
+* Failure recovery: by rolling back to a previous checkpoint
+
+* Improved response time: by restarting applications from checkpoints
+  instead of from scratch.
+
+* Improved system utilization: by suspending long running CPU
+  intensive jobs and resuming them when load decreases.
+
+* Fault resilience: by migrating applications off faulty hosts.
+
+* Dynamic load balancing: by migrating applications to less loaded
+  hosts.
+
+* Improved service availability and administration: by migrating
+  applications before host maintenance so that they continue to run
+  with minimal downtime
+
+* Time-travel: by taking periodic checkpoints and restarting from
+  any previous checkpoint.
+
+Compared to hypervisor approaches, application C/R is more lightweight
+since it need only save the state associated with applications, while
+operating system data structures (e.g. buffer cache, drivers state
+and the like) are uninteresting.
+
+
+Overall design
+==============
+
+Checkpoint and restart are done in the kernel as much as possible.
+Two new system calls are introduced to provide C/R: sys_checkpoint()
+and sys_restart(). They both operate on a process tree (hierarchy),
+either a whole container or a subtree of a container.
+
+Checkpointing entire containers ensures that there are no dependencies
+on anything outside the container, which guarantees that a matching
+restart will succeed (assuming that the file system state remains
+consistent). However, it requires that users will always run the tasks
+that they wish to checkpoint inside containers. This is ideal for,
+e.g., private virtual servers and the like.
+
+In contrast, when checkpointing a subtree of a container it is up to
+the user to ensure that dependencies either don't exist or can be
+safely ignored. This is useful, for instance, for HPC scenarios or
+even a user that would like to periodically checkpoint a long-running
+batch job.
+
+An additional system call, a la madvise(), is planned, so that tasks
+can advise the kernel how to handle specific resources. For instance,
+a task could ask to skip a memory area at checkpoint to save space,
+or to use a preset file descriptor at restart instead of restoring it
+from the checkpoint image. It will provide the flexibility that is
+particularly useful to address the needs of a diverse crowd of users
+and use-cases.
+
+Syscall sys_checkpoint() is given a pid that indicates the top of the
+hierarchy, a file descriptor to store the image, and flags. The code
+serializes internal user- and kernel-state and writes it out to the
+file descriptor. The resulting image is stream-able. The processes are
+expected to be frozen for the duration of the checkpoint.
+
+In general, a checkpoint consists of 5 steps:
+1. Pre-dump
+2. Freeze the container/subtree
+3. Save tasks' and kernel state		<-- sys_checkpoint()
+4. Thaw (or kill) the container/subtree
+5. Post-dump
+
+Step 3 is done by calling sys_checkpoint(). Steps 1 and 5 are an
+optimization to reduce application downtime. In particular, "pre-dump"
+works before freezing the container, e.g. the pre-copy for live
+migration, and "post-dump" works after the container resumes
+execution, e.g. write-back the data to secondary storage.
+
+The kernel exports a relatively opaque 'blob' of data to userspace
+which can then be handed to the new kernel at restart time.  The
+'blob' contains data and state of select portions of kernel structures
+such as VMAs and mm_structs, as well as copies of the actual memory
+that the tasks use. Any changes in this blob's format between kernel
+revisions can be handled by an in-userspace conversion program.
+
+To restart, userspace first create a process hierarchy that matches
+that of the checkpoint, and each task calls sys_restart(). The syscall
+reads the saved kernel state from a file descriptor, and re-creates
+the resources that the tasks need to resume execution. The restart
+code is executed by each task that is restored in the new hierarchy to
+reconstruct its own state.
+
+In general, a restart consists of 3 steps:
+1. Create hierarchy
+2. Restore tasks' and kernel state	<-- sys_restart()
+3. Resume userspace (or freeze tasks)
+
+Because the process hierarchy, during restart in created in userspace,
+the restarting tasks have the flexibility to prepare before calling
+sys_restart().
+
+
+Checkpoint image format
+=======================
+
+The checkpoint image format is built of records that consist of a
+pre-header identifying its contents, followed by a payload. This
+format allow userspace tools to easily parse and skip through the
+image without requiring intimate knowledge of the data. It will also
+be handy to enable parallel checkpointing in the future where multiple
+threads interleave data from multiple processes into a single stream.
+
+The pre-header is defined by 'struct ckpt_hdr' as follows: @type
+identifies the type of the payload, @len tells its length in bytes
+including the pre-header.
+
+struct ckpt_hdr {
+	__s32 type;
+	__s32 len;
+};
+
+The pre-header must be the first component in all other headers. For
+instance, the task data is saved in 'struct ckpt_hdr_task', which
+looks something like this:
+
+struct ckpt_hdr_task {
+	struct ckpt_hdr h;
+	__u32 pid;
+	...
+};
+
+THE IMAGE FORMAT IS EXPECTED TO CHANGE over time as more features are
+supported, or as existing features change in the kernel and require to
+adjust their representation. Any such changes will be be handled by
+in-userspace conversion tools.
+
+The general format of the checkpoint image is as follows:
+* Image header
+* Container configuration
+* Task hierarchy
+* Tasks' state
+* Image trailer
+
+The image always begins with a general header that holds a magic
+number, an architecture identifier (little endian format), a format
+version number (@rev), followed by information about the kernel
+(currently version and UTS data). It also holds the time of the
+checkpoint and the flags given to sys_checkpoint(). This header is
+followed by an arch-specific header.
+
+The container configuration section containers information that is
+global to the container. Security (LSM) configuration is one example.
+Network configuration and container-wide mounts may also go here, so
+that the userspace restart coordinator can re-create a suitable
+environment.
+
+The task hierarchy comes next so that userspace tools can read it
+early (even from a stream) and re-create the restarting tasks. This is
+basically an array of all checkpointed tasks, and their relationships
+(parent, siblings, threads, etc).
+
+Then the state of all tasks is saved, in the order that they appear in
+the tasks array above. For each state, we save data like task_struct,
+namespaces, open files, memory layout, memory contents, cpu state,
+signals and signal handlers, etc. For resources that are shared among
+multiple processes, we first checkpoint said resource (and only once),
+and in the task data we give a reference to it. More about shared
+resources below.
+
+Finally, the image always ends with a trailer that holds a (different)
+magic number, serving for sanity check.
+
+
+Shared objects
+==============
+
+Many resources may be shared by multiple tasks (e.g. file descriptors,
+memory address space, etc), or even have multiple references from
+other resources (e.g. a single inode that represents two ends of a
+pipe).
+
+Shared objects are tracked using a hash table (objhash) to ensure that
+they are only checkpointed or restored once. To handle a shared
+object, it is first looked up in the hash table, to determine if is
+the first encounter or a recurring appearance.  The hash table itself
+is not saved as part of the checkpoint image: it is constructed
+dynamically during both checkpoint and restart, and discarded at the
+end of the operation.
+
+During checkpoint, when a shared object is encountered for the first
+time, it is inserted to the hash table, indexed by its kernel address.
+It is assigned an identifier (@objref) in order of appearance, and
+then its state is saved. Subsequent lookups of that object in the hash
+will yield that entry, in which case only the @objref is saved, as
+opposed the entire state of the object.
+
+During restart, shared objects are indexed by their @objref as given
+during the checkpoint. On the first appearance of each shared object,
+a new resource will be created and its state restored from the image.
+Then the object is added to the hash table. Subsequent lookups of the
+same unique identifier in the hash table will yield that entry, and
+then the existing object instance is reused instead of creating
+a new one.
+
+The hash grabs a reference to each object that is inserted, and
+maintains this reference for the entire lifetime of the hash. Thus,
+it is always safe to reference an object that is stored in the hash.
+The hash is "one-way" in the sense that objects that are added are
+never deleted from the hash until the hash is discarded. This, in
+turn, happens only when the checkpoint (or restart) terminates.
+
+Shared objects are thus saved when they are first seen, and _before_
+the parent object that uses them. Therefore by the time the parent
+objects needs them, they should already be in the objhash. The one
+exception is when more than a single shared resource will be restarted
+at once (e.g. like the two ends of a pipe, or all the namespaces in an
+nsproxy). In this case the parent object is dumped first followed by
+the individual sub-resources).
+
+The checkpoint image is stream-able, meaning that restarting from it
+may not require lseek(). This is enforced at checkpoint time, by
+carefully selecting the order of shared objects, to respect the rule
+that an object is always saved before the objects that refers to it.
+
+
+Memory contents format
+======================
+
+The memory contents of a given memory address space (->mm) is dumped
+as a sequence of vma objects, represented by 'struct ckpt_hdr_vma'.
+This header details the vma properties, and a reference to a file
+(if file backed) or an inode (or shared memory) object.
+
+The vma header is followed by the actual contents - but only those
+pages that need to be saved, i.e. dirty pages. They are written in
+chunks of data, where each chunks contains a header that indicates
+that number of pages in the chunk, followed by an array of virtual
+addresses and then an array of actual page contents. The last chunk
+holds zero pages.
+
+To illustrate this, consider a single simple task with two vmas: one
+is file mapped with two dumped pages, and the other is anonymous with
+three dumped pages. The memory dump will look like this:
+
+	ckpt_hdr + ckpt_hdr_vma
+		ckpt_hdr_pgarr (nr_pages = 2)
+			addr1, addr2
+			page1, page2
+		ckpt_hdr_pgarr (nr_pages = 0)
+	ckpt_hdr + ckpt_hdr_vma
+		ckpt_hdr_pgarr (nr_pages = 3)
+		addr3, addr4, addr5
+		page3, page4, page5
+		ckpt_hdr_pgarr (nr_pages = 0)
+
+
+Error handling
+==============
+
+Both checkpoint and restart operations may fail due to a variety of
+reasons. Using a simple, single return value from the system call is
+insufficient to report the reason of a failure.
+
+Instead, both sys_checkpoint() and sys_restart() accept an additional
+argument - a file descriptor to which the kernel writes diagnostic
+and debugging information. Both the checkpoint and restart userspace
+utilities have options to specify a filename to store this log.
+
+In addition, checkpoint provides informative status report upon
+failure in the checkpoint image in the form of (one or more) error
+objects, 'struct ckpt_hdr_err'.  An error objects consists of a
+mandatory pre-header followed by a null character ('\0'), and then a
+string that describes the error. By default, if an error occurs, this
+will be the last object written to the checkpoint image.
+
+Upon failure, the caller can examine the image (e.g. with 'ckptinfo')
+and extract the detailed error message. The leading '\0' is useful if
+one wants to seek back from the end of the checkpoint image, instead
+of parsing the entire image separately.
+
+
+Security
+========
+
+The main question is whether sys_checkpoint() and sys_restart()
+require privileged or unprivileged operation.
+
+Early versions checked capable(CAP_SYS_ADMIN) assuming that we would
+attempt to remove the need for privilege, so that all users could
+safely use it. Arnd Bergmann pointed out that it'd make more sense to
+let unprivileged users use them now, so that we'll be more careful
+about the security as patches roll in.
+
+Checkpoint: the main concern is whether a task that performs the
+checkpoint of another task has sufficient privileges to access its
+state. We address this by requiring that the checkpointer task will be
+able to ptrace the target task, by means of ptrace_may_access() with
+access mode.
+
+Restart: the main concern is that we may allow an unprivileged user to
+feed the kernel with random data. To this end, the restart works in a
+way that does not skip the usual security checks. Task credentials,
+i.e. euid, reuid, and LSM security contexts currently come from the
+caller, not the checkpoint image.  As credentials are restored too,
+the ability of a task that calls sys_restore() to setresuid/setresgid
+to those values must be checked.
+
+Keeping the restart procedure to operate within the limits of the
+caller's credentials means that there various scenarios that cannot
+be supported. For instance, a setuid program that opened a protected
+log file and then dropped privileges will fail the restart, because
+the user won't have enough credentials to reopen the file. In these
+cases, we should probably treat restarting like inserting a kernel
+module: surely the user can cause havoc by providing incorrect data,
+but then again we must trust the root account.
+
+So that's why we don't want CAP_SYS_ADMIN required up-front. That way
+we will be forced to more carefully review each of those features.
+However, this can be controlled with a sysctl-variable.
+
+
+Kernel interfaces
+=================
+
+* To checkpoint a vma, the 'struct vm_operations_struct' needs to
+  provide a method ->checkpoint:
+    int checkpoint(struct ckpt_ctx *, struct vma_struct *)
+  Restart requires a matching (exported) restore:
+    int restore(struct ckpt_ctx *, struct mm_struct *, struct ckpt_hdr_vma *)
+
+* To checkpoint a file, the 'struct file_operations' needs to provide
+  the methods ->checkpoint and ->collect:
+    int checkpoint(struct ckpt_ctx *, struct file *)
+    int collect(struct ckpt_ctx *, struct file *)
+  Restart requires a matching (exported) restore:
+    int restore(struct ckpt_ctx *, struct ckpt_hdr_file *)
+  For most file systems, generic_file_{checkpoint,restore}() can be
+  used.
+
+* To checkpoint a socket, the 'struct proto_ops' needs to provide
+  the methods ->checkpoint, ->collect and ->restore:
+    int checkpoint(struct ckpt_ctx *ctx, struct socket *sock);
+    int collect(struct ckpt_ctx *ctx, struct socket *sock);
+    int restore(struct ckpt_ctx *, struct socket *sock, struct ckpt_hdr_socket *h)
+
diff --git a/Documentation/checkpoint/self_checkpoint.c b/Documentation/checkpoint/self_checkpoint.c
new file mode 100644
index 0000000..27dba0d
--- /dev/null
+++ b/Documentation/checkpoint/self_checkpoint.c
@@ -0,0 +1,69 @@
+/*
+ *  self_checkpoint.c: demonstrate self-checkpoint
+ *
+ *  Copyright (C) 2008 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <math.h>
+#include <sys/syscall.h>
+
+#include <linux/checkpoint.h>
+
+static inline int checkpoint(pid_t pid, int fd, unsigned long flags)
+{
+	return syscall(__NR_checkpoint, pid, fd, flags, CHECKPOINT_FD_NONE);
+}
+
+#define OUTFILE  "/tmp/cr-self.out"
+
+int main(int argc, char *argv[])
+{
+	pid_t pid = getpid();
+	FILE *file;
+	int i, ret;
+
+	close(0);
+	close(2);
+
+	unlink(OUTFILE);
+	file = fopen(OUTFILE, "w+");
+	if (!file) {
+		perror("open");
+		exit(1);
+	}
+	if (dup2(0, 2) < 0) {
+		perror("dup2");
+		exit(1);
+	}
+
+	fprintf(file, "hello, world!\n");
+	fflush(file);
+
+	for (i = 0; i < 1000; i++) {
+		sleep(1);
+		fprintf(file, "count %d\n", i);
+		fflush(file);
+
+		if (i != 2)
+			continue;
+		ret = checkpoint(pid, STDOUT_FILENO, CHECKPOINT_SUBTREE);
+		if (ret < 0) {
+			fprintf(file, "ckpt: %s\n", strerror(errno));
+			exit(2);
+		}
+
+		fprintf(file, "checkpoint ret: %d\n", ret);
+		fflush(file);
+	}
+
+	return 0;
+}
diff --git a/Documentation/checkpoint/self_restart.c b/Documentation/checkpoint/self_restart.c
new file mode 100644
index 0000000..647ce51
--- /dev/null
+++ b/Documentation/checkpoint/self_restart.c
@@ -0,0 +1,40 @@
+/*
+ *  self_restart.c: demonstrate self-restart
+ *
+ *  Copyright (C) 2008 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#define _GNU_SOURCE        /* or _BSD_SOURCE or _SVID_SOURCE */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+#include <linux/checkpoint.h>
+
+static inline int restart(pid_t pid, int fd, unsigned long flags)
+{
+	return syscall(__NR_restart, pid, fd, flags, CHECKPOINT_FD_NONE);
+}
+
+int main(int argc, char *argv[])
+{
+	pid_t pid = getpid();
+	int ret;
+
+	ret = restart(pid, STDIN_FILENO, RESTART_TASKSELF);
+	if (ret < 0)
+		perror("restart");
+
+	printf("should not reach here !\n");
+
+	return 0;
+}
diff --git a/Documentation/checkpoint/usage.txt b/Documentation/checkpoint/usage.txt
new file mode 100644
index 0000000..c6fc045
--- /dev/null
+++ b/Documentation/checkpoint/usage.txt
@@ -0,0 +1,247 @@
+
+	      How to use Checkpoint-Restart
+	=========================================
+
+
+API
+===
+
+The API consists of three new system calls:
+
+* long checkpoint(pid_t pid, int fd, unsigned long flag, int logfd);
+
+ Checkpoint a (sub-)container whose root task is identified by @pid,
+ to the open file indicated by @fd. If @logfd isn't -1, it indicates
+ an open file to which error and debug messages are written. @flags
+ may be one or more of:
+   - CHECKPOINT_SUBTREE : allow checkpoint of sub-container
+ (other value are not allowed).
+
+ Returns: a positive checkpoint identifier (ckptid) upon success, 0 if
+ it returns from a restart, and -1 if an error occurs. The ckptid will
+ uniquely identify a checkpoint image, for as long as the checkpoint
+ is kept in the kernel (e.g. if one wishes to keep a checkpoint, or a
+ partial checkpoint, residing in kernel memory).
+
+* long sys_restart(pid_t pid, int fd, unsigned long flags, int logfd);
+
+ Restart a process hierarchy from a checkpoint image that is read from
+ the blob stored in the file indicated by @fd.  If @logfd isn't -1, it
+ indicates an open file to which error and debug messages are written.
+ @flags will have future meaning (must be 0 for now). @pid indicates
+ the root of the hierarchy as seen in the coordinator's pid-namespace,
+ and is expected to be a child of the coordinator. @flags may be one
+ or more of:
+   - RESTART_TASKSELF : (self) restart of a single process
+   - RESTART_FROEZN : processes remain frozen once restart completes
+   - RESTART_GHOST : process is a ghost (placeholder for a pid)
+ (Note that this argument may mean 'ckptid' to identify an in-kernel
+ checkpoint image, with some @flags in the future).
+
+ Returns: -1 if an error occurs, 0 on success when restarting from a
+ "self" checkpoint, and return value of system call at the time of the
+ checkpoint when restarting from an "external" checkpoint.
+
+ (If a process was frozen for checkpoint while in userspace, it will
+ resume running in userspace exactly where it was interrupted. If it
+ was frozen while in kernel doing a syscall, it will return what the
+ syscall returned when interrupted/completed, and proceed from there
+ as if it had only been frozen and then thawed. Finally, if it did a
+ self-checkpoint, it will resume to the first instruction after the
+ call to checkpoint(2), having returned 0, to indicate whether the
+ return is from the checkpoint or a restart).
+
+* int clone_with_pid(unsigned long clone_flags, void *news,
+		     int *parent_tidptr, int *child_tidptr,
+		     struct target_pid_set *pid_set)
+
+  struct target_pid_set {
+	 int num_pids;
+	 pid_t *target_pids;
+  }
+
+ Container restart requires that a task have the same pid it had when
+ it was checkpointed. When containers are nested the tasks within the
+ containers exist in multiple pid namespaces and hence have multiple
+ pids to specify during restart.
+
+ clone_with_pids(), intended for use during restart, is similar to
+ clone(), except that it takes a 'target_pid_set' parameter. This
+ parameter lets caller choose specific pid numbers for the child
+ process, in the process's active and ancestor pid namespaces.
+
+ Unlike clone(), clone_with_pids() needs CAP_SYS_ADMIN, at least for
+ now, to prevent unprivileged processes from misusing this interface.
+
+ If a target-pid is 0, the kernel continues to assign a pid for the
+ process in that namespace. If a requested pid is taken, the system
+ call fails with -EBUSY. If 'pid_set.num_pids' exceeds the current
+ nesting level of pid namespaces, the system call fails with -EINVAL.
+
+
+Sysctl/proc
+===========
+
+/proc/sys/kernel/ckpt_unpriv_allowed		[default = 1]
+  controls whether c/r operation is allowed for unprivileged users
+
+
+Operation
+=========
+
+The granularity of a checkpoint usually is a process hierarchy. The
+'pid' argument is interpreted in the caller's pid namespace. So to
+checkpoint a container whose init task (pid 1 in that pidns) appears
+as pid 3497 the caller's pidns, the caller must use pid 3497. Passing
+pid 1 will attempt to checkpoint the caller's container, and if the
+caller isn't privileged and init is owned by root, it will fail.
+
+Unless the CHECKPOINT_SUBTREE flag is set, if the caller passes a pid
+which does not refer to a container's init task, then sys_checkpoint()
+would return -EINVAL.
+
+We assume that during checkpoint and restart the container state is
+quiescent. During checkpoint, this means that all affected tasks are
+frozen (or otherwise stopped). During restart, this means that all
+affected tasks are executing the sys_restart() call. In both cases, if
+there are other tasks possible sharing state with the container, they
+must not modify it during the operation. It is the responsibility of
+the caller to follow this requirement.
+
+If the assumption that all tasks are frozen and that there is no other
+sharing doesn't hold - then the results of the operation are undefined
+(just as, e.g. not calling execve() immediately after vfork() produces
+undefined results). In particular, either checkpoint will fail, or it
+may produce a checkpoint image that can't be restarted, or (unlikely)
+the restart may produce a container whose state does not match that of
+the original container.
+
+
+User tools
+==========
+
+* checkpoint(1): a tool to perform a checkpoint of a container/subtree
+* restart(1): a tool to restart a container/subtree
+* ckptinfo: a tool to examine a checkpoint image
+
+It is best to use the dedicated user tools for checkpoint and restart.
+
+If you insist, then here is a code snippet that illustrates how a
+checkpoint is initiated by a process inside a container - the logic is
+similar to fork():
+	...
+	ckptid = checkpoint(0, ...);
+	switch (crid) {
+	case -1:
+		perror("checkpoint failed");
+		break;
+	default:
+		fprintf(stderr, "checkpoint succeeded, CRID=%d\n", ret);
+		/* proceed with execution after checkpoint */
+		...
+		break;
+	case 0:
+		fprintf(stderr, "returned after restart\n");
+		/* proceed with action required following a restart */
+		...
+		break;
+	}
+	...
+
+And to initiate a restart, the process in an empty container can use
+logic similar to execve():
+	...
+	if (restart(pid, ...) < 0)
+		perror("restart failed");
+	/* only get here if restart failed */
+	...
+
+Note, that the code also supports "self" checkpoint, where a process
+can checkpoint itself. This mode does not capture the relationships of
+the task with other tasks, or any shared resources. It is useful for
+application that wish to be able to save and restore their state.
+They will either not use (or care about) shared resources, or they
+will be aware of the operations and adapt suitably after a restart.
+The code above can also be used for "self" checkpoint.
+
+
+You may find the following sample programs useful:
+
+* checkpoint.c: accepts a 'pid' and checkpoint that task to stdout
+* self_checkpoint.c: a simple test program doing self-checkpoint
+* self_restart.c: restarts a (self-) checkpoint image from stdin
+
+See also the utilities 'checkpoint' and 'restart' (from user-cr).
+
+
+"External" checkpoint
+=====================
+
+To do "external" checkpoint, you need to first freeze that other task
+either using the freezer cgroup.
+
+Restart does not preserve the original PID yet, (because we haven't
+solved yet the fork-with-specific-pid issue). In a real scenario, you
+probably want to first create a new names space, and have the init
+task there call 'sys_restart()'.
+
+I tested it this way:
+	$ ./test &
+	[1] 3493
+
+	$ echo 3493 > /cgroup/0/tasks
+	$ echo FROZEN > /cgroup/0/freezer.state
+	$ ./checkpoint 3493 > ckpt.image
+
+	$ mv /tmp/cr-test.out /tmp/cr-test.out.orig
+	$ cp /tmp/cr-test.out.orig /tmp/cr-test.out
+
+	$ echo THAWED > /cgroup/0/freezer.state
+
+	$ ./self_restart < ckpt.image
+Now compare the output of the two output files.
+
+
+"Self" checkpoint
+================
+
+To do self-checkpoint, you can incorporate the code from
+self_checkpoint.c into your application.
+
+Here is how to test the self-checkpoint:
+	$ ./self_checkpoint > self.image &
+	[1] 3512
+
+	$ sleep 3
+	$ mv /tmp/cr-self.out /tmp/cr-self.out.orig
+	$ cp /tmp/cr-self.out.orig /tmp/cr-self.out
+
+	$ cat /tmp/cr-self.out
+	hello, world!
+	count 0
+	count 1
+	count 2
+	checkpoint ret: 1
+	count 3
+	...
+
+	$ sed -i 's/count/xxxxx/g' /tmp/cr-self.out
+
+	$ ./self_restart < self.image &
+
+Now compare the output of the two output files.
+	$ cat /tmp/cr-self.out
+	hello, world!
+	xxxxx 0
+	xxxxx 1
+	xxxxx 2
+	checkpoint ret: 0
+	count 3
+	...
+
+
+Note how in test.c we close stdin, stdout, stderr - that's because
+currently we only support regular files (not ttys/ptys).
+
+If you check the output of ps, you'll see that "self_restart" changed
+its name to "test" or "self_checkpoint", as expected.
-- 
1.7.2.2

Re: [PATCH 05/19] c/r: documentation

[Dan Smith]

DS> Cc: linux-api@vger.kernel.org
DS> Cc: linux-mm@kvack.org
DS> Cc: netdev@vger.kernel.org
DS> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>

My apologies to the above mentioned.  I didn't mean to git-send-email
this set.  Please ignore.

-- 
Dan Smith
IBM Linux Technology Center
email: danms@us.ibm.com

--
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[PATCH 07/19] c/r: basic infrastructure for checkpoint/restart

[Dan Smith]

From: Oren Laadan <orenl@cs.columbia.edu>

Add those interfaces, as well as helpers needed to easily manage the
file format. The code is roughly broken out as follows:

kernel/checkpoint/sys.c - user/kernel data transfer, as well as setup
  of the c/r context (a per-checkpoint data structure for housekeeping)

kernel/checkpoint/checkpoint.c - output wrappers and checkpoint handling

kernel/checkpoint/restart.c - input wrappers and restart handling

kernel/checkpoint/process.c - c/r of task data

For now, we can only checkpoint the 'current' task ("self" checkpoint),
and the 'pid' argument to the syscall is ignored.

Patches to add the per-architecture support as well as the actual
work to do the memory checkpoint follow in subsequent patches.

Changelog[v21]:
  - Complain if checkpoint_hdr.h included without CONFIG_CHECKPOINT
  - Do not include checkpoint_hdr.h explicitly
  - Consolidate ckpt_read/write with kernel_read/write
  - Reorganize code:move checkpoint/* to kernel/checkpoint/*
  - [Christoffer Dall] Fix trivial bug in ckpt_msg macro
Changelog[v20]:
  - Export key symbols to enable c/r from kernel modules
Changelog[v19]:
  - [Serge Hallyn] Use ckpt_err() to for bad header values
Changelog[v19-rc3]:
  - sys_{checkpoint,restart} to use ptregs prototype
Changelog[v19-rc1]:
  - Set ctx->errno in do_ckpt_msg() if needed
  - Document prototype of ckpt_write_err in header
  - Update prototype of ckpt_read_obj()
  - Fix up headers so we can munge them for use by userspace
  - [Matt Helsley] Check for empty string for _ckpt_write_err()
  - [Matt Helsley] Add cpp definitions for enums
  - [Serge Hallyn] Add global section container to image format
  - [Matt Helsley] Fix total byte read/write count for large images
  - ckpt_read_buf_type() to accept max payload (excludes ckpt_hdr)
  - [Serge Hallyn] Define new api for error and debug logging
  - Use logfd in sys_{checkpoint,restart}
Changelog[v18]:
  - Detect error-headers in input data on restart, and abort.
  - Standard format for checkpoint error strings (and documentation)
  - [Matt Helsley] Rename headerless struct ckpt_hdr_* to struct ckpt_*
  - [Dan Smith] Add an errno validation function
  - Add ckpt_read_payload(): read a variable-length object (no header)
  - Add ckpt_read_string(): same for strings (ensures null-terminated)
  - Add ckpt_read_consume(): consumes next object without processing
Changelog[v17]:
  - Fix compilation for architectures that don't support checkpoint
  - Save/restore t->{set,clear}_child_tid
  - Restart(2) isn't idempotent: must return -EINTR if interrupted
  - ckpt_debug does not depend on DYNAMIC_DEBUG, on by default
  - Export generic checkpoint headers to userespace
  - Fix comment for prototype of sys_restart
  - Have ckpt_debug() print global-pid and __LINE__
  - Only save and test kernel constants once (in header)
Changelog[v16]:
  - Split ctx->flags to ->uflags (user flags) and ->kflags (kernel flags)
  - Introduce __ckpt_write_err() and ckpt_write_err() to report errors
  - Allow @ptr == NULL to write (or read) header only without payload
  - Introduce _ckpt_read_obj_type()
Changelog[v15]:
  - Replace header buffer in ckpt_ctx (hbuf,hpos) with kmalloc/kfree()
Changelog[v14]:
  - Cleanup interface to get/put hdr buffers
  - Merge checkpoint and restart code into a single file (per subsystem)
  - Take uts_sem around access to uts->{release,version,machine}
  - Embed ckpt_hdr in all ckpt_hdr_...., cleanup read/write helpers
  - Define sys_checkpoint(0,...) as asking for a self-checkpoint (Serge)
  - Revert use of 'pr_fmt' to avoid tainting whom includes us (Nathan Lynch)
  - Explicitly indicate length of UTS fields in header
  - Discard field 'h->parent' from ckpt_hdr
Changelog[v12]:
  - ckpt_kwrite/ckpt_kread() again use vfs_read(), vfs_write() (safer)
  - Split ckpt_write/ckpt_read() to two parts: _ckpt_write/read() helper
  - Befriend with sparse : explicit conversion to 'void __user *'
  - Redfine 'pr_fmt' instead of using special ckpt_debug()
Changelog[v10]:
  - add ckpt_write_buffer(), ckpt_read_buffer() and ckpt_read_buf_type()
  - force end-of-string in ckpt_read_string() (fix possible DoS)
Changelog[v9]:
  - ckpt_kwrite/ckpt_kread() use file->f_op->write() directly
  - Drop ckpt_uwrite/ckpt_uread() since they aren't used anywhere
Changelog[v6]:
  - Balance all calls to ckpt_hbuf_get() with matching ckpt_hbuf_put()
    (although it's not really needed)
Changelog[v5]:
  - Rename headers files s/ckpt/checkpoint/
Changelog[v2]:
  - Added utsname->{release,version,machine} to checkpoint header
  - Pad header structures to 64 bits to ensure compatibility

Cc: linux-mm@kvack.org
Cc: linux-fsdevel@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
Acked-by: Serge E. Hallyn <serue@us.ibm.com>
Tested-by: Serge E. Hallyn <serue@us.ibm.com>
---
 include/linux/Kbuild             |    3 +
 include/linux/checkpoint.h       |  202 +++++++++++++++++
 include/linux/checkpoint_hdr.h   |  135 +++++++++++
 include/linux/checkpoint_types.h |   44 ++++
 include/linux/magic.h            |    3 +
 include/linux/syscalls.h         |    4 -
 kernel/checkpoint/Makefile       |    6 +-
 kernel/checkpoint/checkpoint.c   |  213 ++++++++++++++++++
 kernel/checkpoint/process.c      |  101 +++++++++
 kernel/checkpoint/restart.c      |  460 +++++++++++++++++++++++++++++++++++++
 kernel/checkpoint/sys.c          |  461 +++++++++++++++++++++++++++++++++++++-
 lib/Kconfig.debug                |   13 +
 12 files changed, 1632 insertions(+), 13 deletions(-)
 create mode 100644 include/linux/checkpoint.h
 create mode 100644 include/linux/checkpoint_hdr.h
 create mode 100644 include/linux/checkpoint_types.h
 create mode 100644 kernel/checkpoint/checkpoint.c
 create mode 100644 kernel/checkpoint/process.c
 create mode 100644 kernel/checkpoint/restart.c

diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index 97319a8..1fe511b 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -81,6 +81,9 @@ header-y += cciss_ioctl.h
 header-y += cdk.h
 header-y += cdrom.h
 header-y += cgroupstats.h
+header-y += checkpoint.h
+header-y += checkpoint_hdr.h
+header-y += checkpoint_types.h
 header-y += chio.h
 header-y += cm4000_cs.h
 header-y += cn_proc.h
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
new file mode 100644
index 0000000..4bb5b8d
--- /dev/null
+++ b/include/linux/checkpoint.h
@@ -0,0 +1,202 @@
+#ifndef _LINUX_CHECKPOINT_H_
+#define _LINUX_CHECKPOINT_H_
+/*
+ *  Generic checkpoint-restart
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#define CHECKPOINT_VERSION  3
+
+/* misc user visible */
+#define CHECKPOINT_FD_NONE	-1
+
+#ifdef __KERNEL__
+#ifdef CONFIG_CHECKPOINT
+
+#include <linux/checkpoint_types.h>
+#include <linux/checkpoint_hdr.h>
+#include <linux/err.h>
+
+/* sycall helpers */
+extern long do_sys_checkpoint(pid_t pid, int fd,
+			      unsigned long flags, int logfd);
+extern long do_sys_restart(pid_t pid, int fd,
+			   unsigned long flags, int logfd);
+
+/* ckpt_ctx: kflags */
+#define CKPT_CTX_CHECKPOINT_BIT		0
+#define CKPT_CTX_RESTART_BIT		1
+#define CKPT_CTX_ERROR_BIT		3
+
+#define CKPT_CTX_CHECKPOINT	(1 << CKPT_CTX_CHECKPOINT_BIT)
+#define CKPT_CTX_RESTART	(1 << CKPT_CTX_RESTART_BIT)
+#define CKPT_CTX_ERROR		(1 << CKPT_CTX_ERROR_BIT)
+
+
+extern int ckpt_kwrite(struct ckpt_ctx *ctx, void *buf, size_t count);
+extern int ckpt_kread(struct ckpt_ctx *ctx, void *buf, size_t count);
+
+extern void _ckpt_hdr_put(struct ckpt_ctx *ctx, void *ptr, int n);
+extern void ckpt_hdr_put(struct ckpt_ctx *ctx, void *ptr);
+extern void *ckpt_hdr_get(struct ckpt_ctx *ctx, int n);
+extern void *ckpt_hdr_get_type(struct ckpt_ctx *ctx, int n, int type);
+
+extern int ckpt_write_obj(struct ckpt_ctx *ctx, struct ckpt_hdr *h);
+extern int ckpt_write_obj_type(struct ckpt_ctx *ctx,
+			       void *ptr, int len, int type);
+extern int ckpt_write_buffer(struct ckpt_ctx *ctx, void *ptr, int len);
+extern int ckpt_write_string(struct ckpt_ctx *ctx, char *str, int len);
+
+extern int _ckpt_read_obj_type(struct ckpt_ctx *ctx,
+			       void *ptr, int len, int type);
+extern int _ckpt_read_buffer(struct ckpt_ctx *ctx, void *ptr, int len);
+extern int _ckpt_read_string(struct ckpt_ctx *ctx, void *ptr, int len);
+extern void *ckpt_read_obj_type(struct ckpt_ctx *ctx, int len, int type);
+extern void *ckpt_read_buf_type(struct ckpt_ctx *ctx, int max, int type);
+extern int ckpt_read_payload(struct ckpt_ctx *ctx,
+			     void **ptr, int max, int type);
+extern char *ckpt_read_string(struct ckpt_ctx *ctx, int max);
+extern int ckpt_read_consume(struct ckpt_ctx *ctx, int len, int type);
+
+extern long do_checkpoint(struct ckpt_ctx *ctx, pid_t pid);
+extern long do_restart(struct ckpt_ctx *ctx, pid_t pid);
+
+/* task */
+extern int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t);
+extern int restore_task(struct ckpt_ctx *ctx);
+
+static inline int ckpt_validate_errno(int errno)
+{
+	return (errno >= 0) && (errno < MAX_ERRNO);
+}
+
+/* debugging flags */
+#define CKPT_DBASE	0x1		/* anything */
+#define CKPT_DSYS	0x2		/* generic (system) */
+#define CKPT_DRW	0x4		/* image read/write */
+
+#define CKPT_DDEFAULT	0xffff		/* default debug level */
+
+#ifndef CKPT_DFLAG
+#define CKPT_DFLAG	0xffff		/* everything */
+#endif
+
+#ifdef CONFIG_CHECKPOINT_DEBUG
+extern unsigned long ckpt_debug_level;
+
+/*
+ * This is deprecated
+ */
+/* use this to select a specific debug level */
+#define _ckpt_debug(level, fmt, args...)				\
+	do {								\
+		if (ckpt_debug_level & (level))				\
+			printk(KERN_DEBUG "[%d:%d:c/r:%s:%d] " fmt,	\
+				current->pid,				\
+				current->nsproxy ?			\
+				task_pid_vnr(current) : -1,		\
+				__func__, __LINE__, ## args);		\
+	} while (0)
+
+/*
+ * CKPT_DBASE is the base flags, doesn't change
+ * CKPT_DFLAG is to be redfined in each source file
+ */
+#define ckpt_debug(fmt, args...)  \
+	_ckpt_debug(CKPT_DBASE | CKPT_DFLAG, fmt, ## args)
+
+#else
+
+/*
+ * This is deprecated
+ */
+#define _ckpt_debug(level, fmt, args...)	do { } while (0)
+#define ckpt_debug(fmt, args...)		do { } while (0)
+
+#endif /* CONFIG_CHECKPOINT_DEBUG */
+
+/*
+ * prototypes for the new logging api
+ */
+
+extern void ckpt_msg_lock(struct ckpt_ctx *ctx);
+extern void ckpt_msg_unlock(struct ckpt_ctx *ctx);
+
+extern void _do_ckpt_msg(struct ckpt_ctx *ctx, int err, char *fmt, ...);
+extern void do_ckpt_msg(struct ckpt_ctx *ctx, int err, char *fmt, ...);
+
+/*
+ * Append formatted msg to ctx->msg[ctx->msg_len].
+ * Must be called after expanding format.
+ * May be called under spinlock.
+ * Must be called under ckpt_msg_lock().
+ */
+extern void _ckpt_msg_append(struct ckpt_ctx *ctx, char *fmt, ...);
+
+/*
+ * Write ctx->msg to all relevant places.
+ * Must not be called under spinlock.
+ * Must be called under ckpt_msg_lock().
+ */
+extern void _ckpt_msg_complete(struct ckpt_ctx *ctx);
+
+/*
+ * Append an enhanced formatted message to ctx->msg.
+ * This will not write the message out to the applicable files, so
+ * the caller will have to use _ckpt_msg_complete() to finish up.
+ * @ctx must be a valid checkpoint context.
+ * @fmt is the extended format
+ *
+ * Must be called with ckpt_msg_lock held.
+ */
+#define _ckpt_msg(ctx, fmt, args...) do {	\
+	_do_ckpt_msg(ctx, 0, fmt, ##args);	\
+} while (0)
+
+/*
+ * Append an enhanced formatted message to ctx->msg.
+ * This will take the ckpt_msg_lock and also write the message out
+ * to the applicable files by calling _ckpt_msg_complete().
+ * @ctx must be a valid checkpoint context.
+ * @fmt is the extended format
+ *
+ * Must not be called under spinlock.
+ */
+#define ckpt_msg(ctx, fmt, args...) do {	\
+	do_ckpt_msg(ctx, 0, fmt, ##args);	\
+} while (0)
+
+/*
+ * Report an error.
+ * This will take the ckpt_msg_lock and also write the message out
+ * to the applicable files by calling _ckpt_msg_complete().
+ * @ctx must be a valid checkpoint context.
+ * @err is the error value
+ * @fmt is the extended format
+ *
+ * Must not be called under spinlock.
+ */
+
+#define ckpt_err(ctx, err, fmt, args...) do {				\
+	do_ckpt_msg(ctx, err, "[E @ %s:%d]" fmt, __func__, __LINE__, ##args); \
+} while (0)
+
+/*
+ * Same as ckpt_err() but
+ *	must be called with ctx->msg_mutex held
+ *	can be called under spinlock
+ *	must be followed by a call to _ckpt_msg_complete()
+ */
+#define _ckpt_err(ctx, err, fmt, args...) do {				\
+	_do_ckpt_msg(ctx, err, "[E @ %s:%d]" fmt, __func__, __LINE__, ##args); \
+} while (0)
+
+#endif /* CONFIG_CHECKPOINT */
+#endif /* __KERNEL__ */
+
+#endif /* _LINUX_CHECKPOINT_H_ */
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
new file mode 100644
index 0000000..7ccebc7
--- /dev/null
+++ b/include/linux/checkpoint_hdr.h
@@ -0,0 +1,135 @@
+#ifndef _CHECKPOINT_CKPT_HDR_H_
+#define _CHECKPOINT_CKPT_HDR_H_
+/*
+ *  Generic container checkpoint-restart
+ *
+ *  Copyright (C) 2008-2010 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#ifndef __KERNEL__
+#include <sys/types.h>
+#include <linux/types.h>
+#endif
+
+#ifdef __KERNEL__
+#include <linux/types.h>
+
+#ifndef CONFIG_CHECKPOINT
+#error linux/checkpoint_hdr.h included directly (without CONFIG_CHECKPOINT)
+#endif
+
+#endif
+
+#include <linux/utsname.h>
+
+/*
+ * To maintain compatibility between 32-bit and 64-bit architecture flavors,
+ * keep data 64-bit aligned: use padding for structure members, and use
+ * __attribute__((aligned (8))) for the entire structure.
+ *
+ * Quoting Arnd Bergmann:
+ *   "This structure has an odd multiple of 32-bit members, which means
+ *   that if you put it into a larger structure that also contains 64-bit
+ *   members, the larger structure may get different alignment on x86-32
+ *   and x86-64, which you might want to avoid. I can't tell if this is
+ *   an actual problem here. ... In this case, I'm pretty sure that
+ *   sizeof(ckpt_hdr_task) on x86-32 is different from x86-64, since it
+ *   will be 32-bit aligned on x86-32."
+ */
+
+/*
+ * header format: 'struct ckpt_hdr' must prefix all other headers. Therfore
+ * when a header is passed around, the information about it (type, size)
+ * is readily available. Structs that include a struct ckpt_hdr are named
+ * struct ckpt_hdr_* by convention (usualy the struct ckpt_hdr is the first
+ * member).
+ */
+struct ckpt_hdr {
+	__u32 type;
+	__u32 len;
+} __attribute__((aligned(8)));
+
+/* header types */
+enum {
+	CKPT_HDR_HEADER = 1,
+#define CKPT_HDR_HEADER CKPT_HDR_HEADER
+	CKPT_HDR_CONTAINER,
+#define CKPT_HDR_CONTAINER CKPT_HDR_CONTAINER
+	CKPT_HDR_BUFFER,
+#define CKPT_HDR_BUFFER CKPT_HDR_BUFFER
+	CKPT_HDR_STRING,
+#define CKPT_HDR_STRING CKPT_HDR_STRING
+
+	CKPT_HDR_TASK = 101,
+#define CKPT_HDR_TASK CKPT_HDR_TASK
+
+	CKPT_HDR_TAIL = 9001,
+#define CKPT_HDR_TAIL CKPT_HDR_TAIL
+
+	CKPT_HDR_ERROR = 9999,
+#define CKPT_HDR_ERROR CKPT_HDR_ERROR
+};
+
+/* kernel constants */
+struct ckpt_const {
+	/* task */
+	__u16 task_comm_len;
+	/* uts */
+	__u16 uts_release_len;
+	__u16 uts_version_len;
+	__u16 uts_machine_len;
+} __attribute__((aligned(8)));
+
+/* checkpoint image header */
+struct ckpt_hdr_header {
+	struct ckpt_hdr h;
+	__u64 magic;
+
+	__u16 _padding;
+
+	__u16 major;
+	__u16 minor;
+	__u16 patch;
+	__u16 rev;
+
+	struct ckpt_const constants;
+
+	__u64 time;	/* when checkpoint taken */
+	__u64 uflags;	/* uflags from checkpoint */
+
+	/*
+	 * the header is followed by three strings:
+	 *   char release[const.uts_release_len];
+	 *   char version[const.uts_version_len];
+	 *   char machine[const.uts_machine_len];
+	 */
+} __attribute__((aligned(8)));
+
+/* checkpoint image trailer */
+struct ckpt_hdr_tail {
+	struct ckpt_hdr h;
+	__u64 magic;
+} __attribute__((aligned(8)));
+
+/* container configuration section header */
+struct ckpt_hdr_container {
+	struct ckpt_hdr h;
+} __attribute__((aligned(8)));;
+
+/* task data */
+struct ckpt_hdr_task {
+	struct ckpt_hdr h;
+	__u32 state;
+	__u32 exit_state;
+	__u32 exit_code;
+	__u32 exit_signal;
+
+	__u64 set_child_tid;
+	__u64 clear_child_tid;
+} __attribute__((aligned(8)));
+
+#endif /* _CHECKPOINT_CKPT_HDR_H_ */
diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
new file mode 100644
index 0000000..13d6dd5
--- /dev/null
+++ b/include/linux/checkpoint_types.h
@@ -0,0 +1,44 @@
+#ifndef _LINUX_CHECKPOINT_TYPES_H_
+#define _LINUX_CHECKPOINT_TYPES_H_
+/*
+ *  Generic checkpoint-restart
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#ifdef __KERNEL__
+
+#include <linux/fs.h>
+
+struct ckpt_ctx {
+	int crid;		/* unique checkpoint id */
+
+	pid_t root_pid;		/* container identifier */
+
+	unsigned long kflags;	/* kerenl flags */
+	unsigned long uflags;	/* user flags */
+	unsigned long oflags;	/* restart: uflags from checkpoint */
+
+	struct file *file;	/* input/output file */
+	struct file *logfile;	/* status/debug log file */
+	loff_t total;		/* total read/written */
+
+	struct task_struct *tsk;/* checkpoint: current target task */
+	char err_string[256];	/* checkpoint: error string */
+
+	int errno;		/* errno that caused failure */
+
+#define CKPT_MSG_LEN 1024
+	char fmt[CKPT_MSG_LEN];
+	char msg[CKPT_MSG_LEN];
+	int msglen;
+	struct mutex msg_mutex;
+};
+
+#endif /* __KERNEL__ */
+
+#endif /* _LINUX_CHECKPOINT_TYPES_H_ */
diff --git a/include/linux/magic.h b/include/linux/magic.h
index ff690d0..30cd986 100644
--- a/include/linux/magic.h
+++ b/include/linux/magic.h
@@ -59,4 +59,7 @@
 #define SOCKFS_MAGIC		0x534F434B
 #define V9FS_MAGIC		0x01021997
 
+#define CHECKPOINT_MAGIC_HEAD  0x00feed0cc0a2d200LL
+#define CHECKPOINT_MAGIC_TAIL  0x002d2a0cc0deef00LL
+
 #endif /* __LINUX_MAGIC_H__ */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 20be1a6..cacc27a 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -820,10 +820,6 @@ asmlinkage long sys_fanotify_init(unsigned int flags, unsigned int event_f_flags
 asmlinkage long sys_fanotify_mark(int fanotify_fd, unsigned int flags,
 				  u64 mask, int fd,
 				  const char  __user *pathname);
-asmlinkage long sys_checkpoint(pid_t pid, int fd, unsigned long flags,
-			       int logfd);
-asmlinkage long sys_restart(pid_t pid, int fd, unsigned long flags,
-			    int logfd);
 
 int kernel_execve(const char *filename, const char *const argv[], const char *const envp[]);
 
diff --git a/kernel/checkpoint/Makefile b/kernel/checkpoint/Makefile
index 8a32c6f..99364cc 100644
--- a/kernel/checkpoint/Makefile
+++ b/kernel/checkpoint/Makefile
@@ -2,4 +2,8 @@
 # Makefile for linux checkpoint/restart.
 #
 
-obj-$(CONFIG_CHECKPOINT) += sys.o
+obj-$(CONFIG_CHECKPOINT) += \
+	sys.o \
+	checkpoint.o \
+	restart.o \
+	process.o
diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
new file mode 100644
index 0000000..75b43e6
--- /dev/null
+++ b/kernel/checkpoint/checkpoint.c
@@ -0,0 +1,213 @@
+/*
+ *  Checkpoint logic and helpers
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+/* default debug level for output */
+#define CKPT_DFLAG  CKPT_DSYS
+
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/time.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/dcache.h>
+#include <linux/mount.h>
+#include <linux/utsname.h>
+#include <linux/magic.h>
+#include <linux/checkpoint.h>
+
+/* unique checkpoint identifier (FIXME: should be per-container ?) */
+static atomic_t ctx_count = ATOMIC_INIT(0);
+
+/**
+ * ckpt_write_obj - write an object
+ * @ctx: checkpoint context
+ * @h: object descriptor
+ */
+int ckpt_write_obj(struct ckpt_ctx *ctx, struct ckpt_hdr *h)
+{
+	_ckpt_debug(CKPT_DRW, "type %d len %d\n", h->type, h->len);
+	return ckpt_kwrite(ctx, h, h->len);
+}
+EXPORT_SYMBOL(ckpt_write_obj);
+
+/**
+ * ckpt_write_obj_type - write an object (from a pointer)
+ * @ctx: checkpoint context
+ * @ptr: buffer pointer
+ * @len: buffer size
+ * @type: desired type
+ *
+ * If @ptr is NULL, then write only the header (payload to follow)
+ */
+int ckpt_write_obj_type(struct ckpt_ctx *ctx, void *ptr, int len, int type)
+{
+	struct ckpt_hdr *h;
+	int ret;
+
+	h = ckpt_hdr_get(ctx, sizeof(*h));
+	if (!h)
+		return -ENOMEM;
+
+	h->type = type;
+	h->len = len + sizeof(*h);
+
+	_ckpt_debug(CKPT_DRW, "type %d len %d\n", h->type, h->len);
+	ret = ckpt_kwrite(ctx, h, sizeof(*h));
+	if (ret < 0)
+		goto out;
+	if (ptr)
+		ret = ckpt_kwrite(ctx, ptr, len);
+ out:
+	_ckpt_hdr_put(ctx, h, sizeof(*h));
+	return ret;
+}
+EXPORT_SYMBOL(ckpt_write_obj_type);
+
+/**
+ * ckpt_write_buffer - write an object of type buffer
+ * @ctx: checkpoint context
+ * @ptr: buffer pointer
+ * @len: buffer size
+ */
+int ckpt_write_buffer(struct ckpt_ctx *ctx, void *ptr, int len)
+{
+	return ckpt_write_obj_type(ctx, ptr, len, CKPT_HDR_BUFFER);
+}
+EXPORT_SYMBOL(ckpt_write_buffer);
+
+/**
+ * ckpt_write_string - write an object of type string
+ * @ctx: checkpoint context
+ * @str: string pointer
+ * @len: string length
+ */
+int ckpt_write_string(struct ckpt_ctx *ctx, char *str, int len)
+{
+	return ckpt_write_obj_type(ctx, str, len, CKPT_HDR_STRING);
+}
+EXPORT_SYMBOL(ckpt_write_string);
+
+/***********************************************************************
+ * Checkpoint
+ */
+
+static void fill_kernel_const(struct ckpt_const *h)
+{
+	struct task_struct *tsk;
+	struct new_utsname *uts;
+
+	/* task */
+	h->task_comm_len = sizeof(tsk->comm);
+	/* uts */
+	h->uts_release_len = sizeof(uts->release);
+	h->uts_version_len = sizeof(uts->version);
+	h->uts_machine_len = sizeof(uts->machine);
+}
+
+/* write the checkpoint header */
+static int checkpoint_write_header(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_header *h;
+	struct new_utsname *uts;
+	struct timeval ktv;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_HEADER);
+	if (!h)
+		return -ENOMEM;
+
+	do_gettimeofday(&ktv);
+	uts = utsname();
+
+	h->magic = CHECKPOINT_MAGIC_HEAD;
+	h->major = (LINUX_VERSION_CODE >> 16) & 0xff;
+	h->minor = (LINUX_VERSION_CODE >> 8) & 0xff;
+	h->patch = (LINUX_VERSION_CODE) & 0xff;
+
+	h->rev = CHECKPOINT_VERSION;
+
+	h->uflags = ctx->uflags;
+	h->time = ktv.tv_sec;
+
+	fill_kernel_const(&h->constants);
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+	if (ret < 0)
+		return ret;
+
+	down_read(&uts_sem);
+	ret = ckpt_write_buffer(ctx, uts->release, sizeof(uts->release));
+	if (ret < 0)
+		goto up;
+	ret = ckpt_write_buffer(ctx, uts->version, sizeof(uts->version));
+	if (ret < 0)
+		goto up;
+	ret = ckpt_write_buffer(ctx, uts->machine, sizeof(uts->machine));
+ up:
+	up_read(&uts_sem);
+	return ret;
+}
+
+/* write the container configuration section */
+static int checkpoint_container(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_container *h;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_CONTAINER);
+	if (!h)
+		return -ENOMEM;
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+
+	return ret;
+}
+
+/* write the checkpoint trailer */
+static int checkpoint_write_tail(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_tail *h;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TAIL);
+	if (!h)
+		return -ENOMEM;
+
+	h->magic = CHECKPOINT_MAGIC_TAIL;
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+long do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
+{
+	long ret;
+
+	ret = checkpoint_write_header(ctx);
+	if (ret < 0)
+		goto out;
+	ret = checkpoint_container(ctx);
+	if (ret < 0)
+		goto out;
+	ret = checkpoint_task(ctx, current);
+	if (ret < 0)
+		goto out;
+	ret = checkpoint_write_tail(ctx);
+	if (ret < 0)
+		goto out;
+
+	/* on success, return (unique) checkpoint identifier */
+	ctx->crid = atomic_inc_return(&ctx_count);
+	ret = ctx->crid;
+ out:
+	return ret;
+}
diff --git a/kernel/checkpoint/process.c b/kernel/checkpoint/process.c
new file mode 100644
index 0000000..abd9025
--- /dev/null
+++ b/kernel/checkpoint/process.c
@@ -0,0 +1,101 @@
+/*
+ *  Checkpoint task structure
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+/* default debug level for output */
+#define CKPT_DFLAG  CKPT_DSYS
+
+#include <linux/sched.h>
+#include <linux/checkpoint.h>
+
+/***********************************************************************
+ * Checkpoint
+ */
+
+/* dump the task_struct of a given task */
+static int checkpoint_task_struct(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	struct ckpt_hdr_task *h;
+	int ret;
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TASK);
+	if (!h)
+		return -ENOMEM;
+
+	h->state = t->state;
+	h->exit_state = t->exit_state;
+	h->exit_code = t->exit_code;
+	h->exit_signal = t->exit_signal;
+
+	h->set_child_tid = (unsigned long) t->set_child_tid;
+	h->clear_child_tid = (unsigned long) t->clear_child_tid;
+
+	/* FIXME: save remaining relevant task_struct fields */
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+	if (ret < 0)
+		return ret;
+
+	return ckpt_write_string(ctx, t->comm, TASK_COMM_LEN);
+}
+
+/* dump the entire state of a given task */
+int checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
+{
+	int ret;
+
+	ctx->tsk = t;
+
+	ret = checkpoint_task_struct(ctx, t);
+	ckpt_debug("task %d\n", ret);
+
+	ctx->tsk = NULL;
+	return ret;
+}
+
+/***********************************************************************
+ * Restart
+ */
+
+/* read the task_struct into the current task */
+static int restore_task_struct(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_task *h;
+	struct task_struct *t = current;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TASK);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	memset(t->comm, 0, TASK_COMM_LEN);
+	ret = _ckpt_read_string(ctx, t->comm, TASK_COMM_LEN);
+	if (ret < 0)
+		goto out;
+
+	t->set_child_tid = (int __user *) (unsigned long) h->set_child_tid;
+	t->clear_child_tid = (int __user *) (unsigned long) h->clear_child_tid;
+
+	/* FIXME: restore remaining relevant task_struct fields */
+ out:
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+/* read the entire state of the current task */
+int restore_task(struct ckpt_ctx *ctx)
+{
+	int ret;
+
+	ret = restore_task_struct(ctx);
+	ckpt_debug("task %d\n", ret);
+
+	return ret;
+}
diff --git a/kernel/checkpoint/restart.c b/kernel/checkpoint/restart.c
new file mode 100644
index 0000000..cd9945c
--- /dev/null
+++ b/kernel/checkpoint/restart.c
@@ -0,0 +1,460 @@
+/*
+ *  Restart logic and helpers
+ *
+ *  Copyright (C) 2008-2009 Oren Laadan
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+/* default debug level for output */
+#define CKPT_DFLAG  CKPT_DSYS
+
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/file.h>
+#include <linux/magic.h>
+#include <linux/utsname.h>
+#include <linux/checkpoint.h>
+
+static int _ckpt_read_err(struct ckpt_ctx *ctx, struct ckpt_hdr *h)
+{
+	char *ptr;
+	int len, ret;
+
+	len = h->len - sizeof(*h);
+	ptr = kzalloc(len + 1, GFP_KERNEL);
+	if (!ptr) {
+		ckpt_debug("insufficient memory to report image error\n");
+		return -ENOMEM;
+	}
+
+	ret = ckpt_kread(ctx, ptr, len);
+	if (ret >= 0) {
+		ckpt_debug("%s\n", &ptr[1]);
+		ret = -EIO;
+	}
+
+	kfree(ptr);
+	return ret;
+}
+
+/**
+ * _ckpt_read_obj - read an object (ckpt_hdr followed by payload)
+ * @ctx: checkpoint context
+ * @h: desired ckpt_hdr
+ * @ptr: desired buffer
+ * @len: desired object length (if 0, flexible)
+ * @max: maximum object length (if 0, flexible)
+ *
+ * If @ptr is NULL, then read only the header (payload to follow)
+ */
+static int _ckpt_read_obj(struct ckpt_ctx *ctx, struct ckpt_hdr *h,
+			  void *ptr, int len, int max)
+{
+	int ret;
+
+ again:
+	ret = ckpt_kread(ctx, h, sizeof(*h));
+	if (ret < 0)
+		return ret;
+	_ckpt_debug(CKPT_DRW, "type %d len %d(%d,%d)\n",
+		    h->type, h->len, len, max);
+	if (h->len < sizeof(*h))
+		return -EINVAL;
+
+	if (h->type == CKPT_HDR_ERROR) {
+		ret = _ckpt_read_err(ctx, h);
+		if (ret < 0)
+			return ret;
+		goto again;
+	}
+
+	/* if len specified, enforce, else if maximum specified, enforce */
+	if ((len && h->len != len) || (!len && max && h->len > max))
+		return -EINVAL;
+
+	if (ptr)
+		ret = ckpt_kread(ctx, ptr, h->len - sizeof(struct ckpt_hdr));
+	return ret;
+}
+
+/**
+ * _ckpt_read_obj_type - read an object of some type
+ * @ctx: checkpoint context
+ * @ptr: provided buffer
+ * @len: buffer length
+ * @type: buffer type
+ *
+ * If @ptr is NULL, then read only the header (payload to follow).
+ * @len specifies the expected buffer length (ignored if set to 0).
+ * Returns: actual _payload_ length
+ */
+int _ckpt_read_obj_type(struct ckpt_ctx *ctx, void *ptr, int len, int type)
+{
+	struct ckpt_hdr h;
+	int ret;
+
+	if (len)
+		len += sizeof(struct ckpt_hdr);
+	ret = _ckpt_read_obj(ctx, &h, ptr, len, len);
+	if (ret < 0)
+		return ret;
+	if (h.type != type)
+		return -EINVAL;
+	return h.len - sizeof(h);
+}
+EXPORT_SYMBOL(_ckpt_read_obj_type);
+
+/**
+ * _ckpt_read_buffer - read an object of type buffer (set length)
+ * @ctx: checkpoint context
+ * @ptr: provided buffer
+ * @len: buffer length
+ *
+ * If @ptr is NULL, then read only the header (payload to follow).
+ * @len specifies the expected buffer length (ignored if set to 0).
+ * Returns: _payload_ length.
+ */
+int _ckpt_read_buffer(struct ckpt_ctx *ctx, void *ptr, int len)
+{
+	BUG_ON(!len);
+	return _ckpt_read_obj_type(ctx, ptr, len, CKPT_HDR_BUFFER);
+}
+EXPORT_SYMBOL(_ckpt_read_buffer);
+
+/**
+ * _ckpt_read_string - read an object of type string (set length)
+ * @ctx: checkpoint context
+ * @ptr: provided buffer
+ * @len: string length (including '\0')
+ *
+ * If @ptr is NULL, then read only the header (payload to follow)
+ */
+int _ckpt_read_string(struct ckpt_ctx *ctx, void *ptr, int len)
+{
+	int ret;
+
+	BUG_ON(!len);
+	ret = _ckpt_read_obj_type(ctx, ptr, len, CKPT_HDR_STRING);
+	if (ret < 0)
+		return ret;
+	if (ptr)
+		((char *) ptr)[len - 1] = '\0';	/* always play it safe */
+	return 0;
+}
+EXPORT_SYMBOL(_ckpt_read_string);
+
+/**
+ * ckpt_read_obj - allocate and read an object (ckpt_hdr followed by payload)
+ * @ctx: checkpoint context
+ * @h: object descriptor
+ * @len: desired total length (if 0, flexible)
+ * @max: maximum total length
+ *
+ * Return: new buffer allocated on success, error pointer otherwise
+ */
+static void *ckpt_read_obj(struct ckpt_ctx *ctx, int len, int max)
+{
+	struct ckpt_hdr hh;
+	struct ckpt_hdr *h;
+	int ret;
+
+	ret = ckpt_kread(ctx, &hh, sizeof(hh));
+	if (ret < 0)
+		return ERR_PTR(ret);
+	_ckpt_debug(CKPT_DRW, "type %d len %d(%d,%d)\n",
+		    hh.type, hh.len, len, max);
+	if (hh.len < sizeof(*h))
+		return ERR_PTR(-EINVAL);
+	/* if len specified, enforce, else if maximum specified, enforce */
+	if ((len && hh.len != len) || (!len && max && hh.len > max))
+		return ERR_PTR(-EINVAL);
+
+	h = ckpt_hdr_get(ctx, hh.len);
+	if (!h)
+		return ERR_PTR(-ENOMEM);
+
+	*h = hh;	/* yay ! */
+
+	ret = ckpt_kread(ctx, (h + 1), hh.len - sizeof(struct ckpt_hdr));
+	if (ret < 0) {
+		ckpt_hdr_put(ctx, h);
+		h = ERR_PTR(ret);
+	}
+
+	return h;
+}
+
+/**
+ * ckpt_read_obj_type - allocate and read an object of some type
+ * @ctx: checkpoint context
+ * @len: desired object length
+ * @type: desired object type
+ *
+ * Return: new buffer allocated on success, error pointer otherwise
+ */
+void *ckpt_read_obj_type(struct ckpt_ctx *ctx, int len, int type)
+{
+	struct ckpt_hdr *h;
+
+	BUG_ON(!len);
+
+	h = ckpt_read_obj(ctx, len, len);
+	if (IS_ERR(h))
+		return h;
+
+	if (h->type != type) {
+		ckpt_hdr_put(ctx, h);
+		h = ERR_PTR(-EINVAL);
+	}
+
+	return h;
+}
+EXPORT_SYMBOL(ckpt_read_obj_type);
+
+/**
+ * ckpt_read_buf_type - allocate and read an object of some type (flxible)
+ * @ctx: checkpoint context
+ * @max: maximum payload length
+ * @type: desired object type
+ *
+ * This differs from ckpt_read_obj_type() in that the length of the
+ * incoming object is flexible (up to the maximum specified by @max;
+ * unlimited if @max is 0), as determined by the ckpt_hdr data.
+ *
+ * NOTE: for symmetry with checkpoint, @max is the maximum _payload_
+ * size, excluding the header.
+ *
+ * Return: new buffer allocated on success, error pointer otherwise
+ */
+void *ckpt_read_buf_type(struct ckpt_ctx *ctx, int max, int type)
+{
+	struct ckpt_hdr *h;
+
+	if (max)
+		max += sizeof(struct ckpt_hdr);
+
+	h = ckpt_read_obj(ctx, 0, max);
+	if (IS_ERR(h))
+		return h;
+
+	if (h->type != type) {
+		ckpt_hdr_put(ctx, h);
+		h = ERR_PTR(-EINVAL);
+	}
+
+	return h;
+}
+EXPORT_SYMBOL(ckpt_read_buf_type);
+
+/**
+ * ckpt_read_payload - allocate and read the payload of an object
+ * @ctx: checkpoint context
+ * @max: maximum payload length
+ * @str: pointer to buffer to be allocated (caller must free)
+ * @type: desired object type
+ *
+ * This can be used to read a variable-length _payload_ from the checkpoint
+ * stream. @max limits the size of the resulting buffer.
+ *
+ * Return: actual _payload_ length
+ */
+int ckpt_read_payload(struct ckpt_ctx *ctx, void **ptr, int max, int type)
+{
+	int len, ret;
+
+	len = _ckpt_read_obj_type(ctx, NULL, 0, type);
+	if (len < 0)
+		return len;
+	else if (len > max)
+		return -EINVAL;
+
+	*ptr = kmalloc(len, GFP_KERNEL);
+	if (!*ptr)
+		return -ENOMEM;
+
+	ret = ckpt_kread(ctx, *ptr, len);
+	if (ret < 0) {
+		kfree(*ptr);
+		return ret;
+	}
+
+	return len;
+}
+EXPORT_SYMBOL(ckpt_read_payload);
+
+/**
+ * ckpt_read_string - allocate and read a string (variable length)
+ * @ctx: checkpoint context
+ * @max: maximum acceptable length
+ *
+ * Return: allocate string or error pointer
+ */
+char *ckpt_read_string(struct ckpt_ctx *ctx, int max)
+{
+	char *str;
+	int len;
+
+	len = ckpt_read_payload(ctx, (void **)&str, max, CKPT_HDR_STRING);
+	if (len < 0)
+		return ERR_PTR(len);
+	str[len - 1] = '\0';	/* always play it safe */
+	return str;
+}
+EXPORT_SYMBOL(ckpt_read_string);
+
+/**
+ * ckpt_read_consume - consume the next object of expected type
+ * @ctx: checkpoint context
+ * @len: desired object length
+ * @type: desired object type
+ *
+ * This can be used to skip an object in the input stream when the
+ * data is unnecessary for the restart. @len indicates the length of
+ * the object); if @len is zero the length is unconstrained.
+ */
+int ckpt_read_consume(struct ckpt_ctx *ctx, int len, int type)
+{
+	struct ckpt_hdr *h;
+	int ret = 0;
+
+	h = ckpt_read_obj(ctx, len, 0);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	if (h->type != type)
+		ret = -EINVAL;
+
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+EXPORT_SYMBOL(ckpt_read_consume);
+
+/***********************************************************************
+ * Restart
+ */
+
+static int check_kernel_const(struct ckpt_const *h)
+{
+	struct task_struct *tsk;
+	struct new_utsname *uts;
+
+	/* task */
+	if (h->task_comm_len != sizeof(tsk->comm))
+		return -EINVAL;
+	/* uts */
+	if (h->uts_release_len != sizeof(uts->release))
+		return -EINVAL;
+	if (h->uts_version_len != sizeof(uts->version))
+		return -EINVAL;
+	if (h->uts_machine_len != sizeof(uts->machine))
+		return -EINVAL;
+
+	return 0;
+}
+
+/* read the checkpoint header */
+static int restore_read_header(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_header *h;
+	struct new_utsname *uts = NULL;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_HEADER);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	ret = -EINVAL;
+	if (h->magic != CHECKPOINT_MAGIC_HEAD ||
+	    h->rev != CHECKPOINT_VERSION ||
+	    h->major != ((LINUX_VERSION_CODE >> 16) & 0xff) ||
+	    h->minor != ((LINUX_VERSION_CODE >> 8) & 0xff) ||
+	    h->patch != ((LINUX_VERSION_CODE) & 0xff)) {
+		ckpt_err(ctx, ret, "incompatible kernel version");
+		goto out;
+	}
+	if (h->uflags) {
+		ckpt_err(ctx, ret, "incompatible restart user flags");
+		goto out;
+	}
+
+	ret = check_kernel_const(&h->constants);
+	if (ret < 0) {
+		ckpt_err(ctx, ret, "incompatible kernel constants");
+		goto out;
+	}
+
+	ret = -ENOMEM;
+	uts = kmalloc(sizeof(*uts), GFP_KERNEL);
+	if (!uts)
+		goto out;
+
+	ctx->oflags = h->uflags;
+
+	/* FIX: verify compatibility of release, version and machine */
+	ret = _ckpt_read_buffer(ctx, uts->release, sizeof(uts->release));
+	if (ret < 0)
+		goto out;
+	ret = _ckpt_read_buffer(ctx, uts->version, sizeof(uts->version));
+	if (ret < 0)
+		goto out;
+	ret = _ckpt_read_buffer(ctx, uts->machine, sizeof(uts->machine));
+ out:
+	kfree(uts);
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+/* read the container configuration section */
+static int restore_container(struct ckpt_ctx *ctx)
+{
+	int ret = 0;
+	struct ckpt_hdr_container *h;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_CONTAINER);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+	ckpt_hdr_put(ctx, h);
+
+	return ret;
+}
+
+/* read the checkpoint trailer */
+static int restore_read_tail(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_tail *h;
+	int ret = 0;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TAIL);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	if (h->magic != CHECKPOINT_MAGIC_TAIL)
+		ret = -EINVAL;
+
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+long do_restart(struct ckpt_ctx *ctx, pid_t pid)
+{
+	long ret;
+
+	ret = restore_read_header(ctx);
+	if (ret < 0)
+		return ret;
+	ret = restore_container(ctx);
+	if (ret < 0)
+		return ret;
+	ret = restore_task(ctx);
+	if (ret < 0)
+		return ret;
+	ret = restore_read_tail(ctx);
+
+	/* on success, adjust the return value if needed [TODO] */
+	return ret;
+}
diff --git a/kernel/checkpoint/sys.c b/kernel/checkpoint/sys.c
index a81750a..af8c1bf 100644
--- a/kernel/checkpoint/sys.c
+++ b/kernel/checkpoint/sys.c
@@ -8,12 +8,398 @@
  *  distribution for more details.
  */
 
+/* default debug level for output */
+#define CKPT_DFLAG  CKPT_DSYS
+
 #include <linux/sched.h>
+#include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/syscalls.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/uaccess.h>
+#include <linux/capability.h>
+#include <linux/checkpoint.h>
+
+/*
+ * Helpers to write(read) from(to) kernel space to(from) the checkpoint
+ * image file descriptor (similar to how a core-dump is performed).
+ *
+ *   _ckpt_kwrite() - write a kernel-space buffer to a file
+ *   _ckpt_kread() - read from a file to a kernel-space buffer
+ *
+ *   ckpt_kread() - read from the checkpoint image to a kernel-space buffer
+ *   ckpt_kwrite() - write a kernel-space buffer to the checkpoint image
+ *
+ * They latter two succeed only if the entire read or write succeeds,
+ * and return 0, or negative error otherwise.
+ */
+
+static ssize_t _ckpt_kwrite(struct file *file, void *addr, size_t count)
+{
+	loff_t pos;
+	int ret;
+
+	pos = file_pos_read(file);
+	ret = kernel_write(file, pos, addr, count);
+	if (ret < 0)
+		return ret;
+	file_pos_write(file, pos + ret);
+	return ret;
+}
+
+/* returns 0 on success */
+int ckpt_kwrite(struct ckpt_ctx *ctx, void *addr, size_t count)
+{
+	int ret;
+
+	ret = _ckpt_kwrite(ctx->file, addr, count);
+	if (ret < 0)
+		return ret;
+
+	ctx->total += count;
+	return 0;
+}
+
+static ssize_t _ckpt_kread(struct file *file, void *addr, size_t count)
+{
+	loff_t pos;
+	int ret;
+
+	pos = file_pos_read(file);
+	ret = kernel_read(file, pos, addr, count);
+	if (ret < 0)
+		return ret;
+	file_pos_write(file, pos + ret);
+	return ret;
+}
+
+/* returns 0 on success */
+int ckpt_kread(struct ckpt_ctx *ctx, void *addr, size_t count)
+{
+	int ret;
+
+	ret = _ckpt_kread(ctx->file, addr, count);
+	if (ret < 0)
+		return ret;
+	if (ret != count)
+		return -EPIPE;
+
+	ctx->total += count;
+	return 0;
+}
+
+/**
+ * ckpt_hdr_get - get a hdr of certain size
+ * @ctx: checkpoint context
+ * @len: desired length
+ *
+ * Returns pointer to header
+ */
+void *ckpt_hdr_get(struct ckpt_ctx *ctx, int len)
+{
+	return kzalloc(len, GFP_KERNEL);
+}
+EXPORT_SYMBOL(ckpt_hdr_get);
+
+/**
+ * _ckpt_hdr_put - free a hdr allocated with ckpt_hdr_get
+ * @ctx: checkpoint context
+ * @ptr: header to free
+ * @len: header length
+ *
+ * (requiring 'ptr' makes it easily interchangable with kmalloc/kfree
+ */
+void _ckpt_hdr_put(struct ckpt_ctx *ctx, void *ptr, int len)
+{
+	kfree(ptr);
+}
+EXPORT_SYMBOL(_ckpt_hdr_put);
+
+/**
+ * ckpt_hdr_put - free a hdr allocated with ckpt_hdr_get
+ * @ctx: checkpoint context
+ * @ptr: header to free
+ *
+ * It is assumed that @ptr begins with a 'struct ckpt_hdr'.
+ */
+void ckpt_hdr_put(struct ckpt_ctx *ctx, void *ptr)
+{
+	struct ckpt_hdr *h = (struct ckpt_hdr *) ptr;
+	_ckpt_hdr_put(ctx, ptr, h->len);
+}
+EXPORT_SYMBOL(ckpt_hdr_put);
+
+/**
+ * ckpt_hdr_get_type - get a hdr of certain size
+ * @ctx: checkpoint context
+ * @len: number of bytes to reserve
+ *
+ * Returns pointer to reserved space on hbuf
+ */
+void *ckpt_hdr_get_type(struct ckpt_ctx *ctx, int len, int type)
+{
+	struct ckpt_hdr *h;
+
+	h = ckpt_hdr_get(ctx, len);
+	if (!h)
+		return NULL;
+
+	h->type = type;
+	h->len = len;
+	return h;
+}
+EXPORT_SYMBOL(ckpt_hdr_get_type);
+
+/*
+ * Helpers to manage c/r contexts: allocated for each checkpoint and/or
+ * restart operation, and persists until the operation is completed.
+ */
+
+static void ckpt_ctx_free(struct ckpt_ctx *ctx)
+{
+	if (ctx->file)
+		fput(ctx->file);
+	if (ctx->logfile)
+		fput(ctx->logfile);
+	kfree(ctx);
+}
+
+static struct ckpt_ctx *ckpt_ctx_alloc(int fd, unsigned long uflags,
+				       unsigned long kflags, int logfd)
+{
+	struct ckpt_ctx *ctx;
+	int err;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	ctx->uflags = uflags;
+	ctx->kflags = kflags;
+
+	mutex_init(&ctx->msg_mutex);
+
+	err = -EBADF;
+	ctx->file = fget(fd);
+	if (!ctx->file)
+		goto err;
+	if (logfd == CHECKPOINT_FD_NONE)
+		goto nolog;
+	ctx->logfile = fget(logfd);
+	if (!ctx->logfile)
+		goto err;
+ nolog:
+	return ctx;
+ err:
+	ckpt_ctx_free(ctx);
+	return ERR_PTR(err);
+}
+
+static void ckpt_set_error(struct ckpt_ctx *ctx, int err)
+{
+	ctx->errno = err;
+}
+
+/* helpers to handler log/dbg/err messages */
+void ckpt_msg_lock(struct ckpt_ctx *ctx)
+{
+	if (!ctx)
+		return;
+	mutex_lock(&ctx->msg_mutex);
+	ctx->msg[0] = '\0';
+	ctx->msglen = 1;
+}
+
+void ckpt_msg_unlock(struct ckpt_ctx *ctx)
+{
+	if (!ctx)
+		return;
+	mutex_unlock(&ctx->msg_mutex);
+}
+
+static inline int is_special_flag(char *s)
+{
+	if (*s == '%' && s[1] == '(' && s[2] != '\0' && s[3] == ')')
+		return 1;
+	return 0;
+}
+
+/*
+ * _ckpt_generate_fmt - handle the special flags in the enhanced format
+ * strings used by checkpoint/restart error messages.
+ * @ctx: checkpoint context
+ * @fmt: message format
+ *
+ * The special flags are surrounded by %() to help them visually stand
+ * out.  For instance, %(O) means an objref.  The following special
+ * flags are recognized:
+ *	O: objref
+ *	P: pointer
+ *	T: task
+ *	S: string
+ *	V: variable
+ *
+ * %(O) will be expanded to "[obj %d]".  Likewise P, S, and V, will
+ * also expand to format flags requiring an argument to the subsequent
+ * sprintf or printk.  T will be expanded to a string with no flags,
+ * requiring no further arguments.
+ *
+ * These do not accept any extra flags (i.e. min field width, precision,
+ * etc).
+ *
+ * The caller of ckpt_err() and _ckpt_err() must provide
+ * the additional variabes, in order, to match the @fmt (except for
+ * the T key), e.g.:
+ *
+ *	ckpt_err(ctx, err, "%(T)FILE flags %d %(O)\n", flags, objref);
+ *
+ * May be called under spinlock.
+ * Must be called with ctx->msg_mutex held.  The expanded format
+ * will be placed in ctx->fmt.
+ */
+static void _ckpt_generate_fmt(struct ckpt_ctx *ctx, char *fmt)
+{
+	char *s = ctx->fmt;
+	int len = 0;
+
+	for (; *fmt && len < CKPT_MSG_LEN; fmt++) {
+		if (!is_special_flag(fmt)) {
+			s[len++] = *fmt;
+			continue;
+		}
+		switch (fmt[2]) {
+		case 'O':
+			len += snprintf(s+len, CKPT_MSG_LEN-len, "[obj %%d]");
+			break;
+		case 'P':
+			len += snprintf(s+len, CKPT_MSG_LEN-len, "[ptr %%p]");
+			break;
+		case 'V':
+			len += snprintf(s+len, CKPT_MSG_LEN-len, "[sym %%pS]");
+			break;
+		case 'S':
+			len += snprintf(s+len, CKPT_MSG_LEN-len, "[str %%s]");
+			break;
+		case 'T':
+			if (ctx->tsk)
+				len += snprintf(s+len, CKPT_MSG_LEN-len,
+					"[pid %d tsk %s]",
+					task_pid_vnr(ctx->tsk), ctx->tsk->comm);
+			else
+				len += snprintf(s+len, CKPT_MSG_LEN-len,
+					"[pid -1 tsk NULL]");
+			break;
+		default:
+			printk(KERN_ERR "c/r: bad format specifier %c\n",
+					fmt[2]);
+			BUG();
+		}
+		fmt += 3;
+	}
+	if (len == CKPT_MSG_LEN)
+		s[CKPT_MSG_LEN-1] = '\0';
+	else
+		s[len] = '\0';
+}
+
+static void _ckpt_msg_appendv(struct ckpt_ctx *ctx, int err, char *fmt,
+				va_list ap)
+{
+	int len = ctx->msglen;
+
+	if (err) {
+		len += snprintf(&ctx->msg[len], CKPT_MSG_LEN-len, "[err %d]",
+				 err);
+		if (len > CKPT_MSG_LEN)
+			goto full;
+	}
+
+	len += snprintf(&ctx->msg[len], CKPT_MSG_LEN-len, "[pos %lld]",
+			ctx->total);
+	len += vsnprintf(&ctx->msg[len], CKPT_MSG_LEN-len, fmt, ap);
+	if (len > CKPT_MSG_LEN) {
+full:
+		len = CKPT_MSG_LEN;
+		ctx->msg[CKPT_MSG_LEN-1] = '\0';
+	}
+	ctx->msglen = len;
+}
+
+void _ckpt_msg_append(struct ckpt_ctx *ctx, char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	_ckpt_msg_appendv(ctx, 0, fmt, ap);
+	va_end(ap);
+}
+
+void _ckpt_msg_complete(struct ckpt_ctx *ctx)
+{
+	int ret;
+
+	/* Don't write an empty or uninitialized msg */
+	if (ctx->msglen <= 1)
+		return;
+
+	if (ctx->kflags & CKPT_CTX_CHECKPOINT && ctx->errno) {
+		ret = ckpt_write_obj_type(ctx, NULL, 0, CKPT_HDR_ERROR);
+		if (!ret)
+			ret = ckpt_write_string(ctx, ctx->msg, ctx->msglen);
+		if (ret < 0)
+			printk(KERN_NOTICE "c/r: error string unsaved (%d): %s\n",
+			       ret, ctx->msg+1);
+	}
+
+	if (ctx->logfile) {
+		struct file *logfile = ctx->logfile;
+		loff_t pos = file_pos_read(logfile);
+		ret = kernel_write(logfile, pos, ctx->msg+1, ctx->msglen-1);
+		if (ret > 0)
+			file_pos_write(logfile, pos + ret);
+	}
+
+#ifdef CONFIG_CHECKPOINT_DEBUG
+	printk(KERN_DEBUG "%s", ctx->msg+1);
+#endif
+
+	ctx->msglen = 0;
+}
+
+#define __do_ckpt_msg(ctx, err, fmt) do {		\
+	va_list ap;					\
+	_ckpt_generate_fmt(ctx, fmt);			\
+	va_start(ap, fmt);				\
+	_ckpt_msg_appendv(ctx, err, ctx->fmt, ap);	\
+	va_end(ap);					\
+} while (0)
+
+void _do_ckpt_msg(struct ckpt_ctx *ctx, int err, char *fmt, ...)
+{
+	__do_ckpt_msg(ctx, err, fmt);
+}
+
+void do_ckpt_msg(struct ckpt_ctx *ctx, int err, char *fmt, ...)
+{
+	if (!ctx)
+		return;
+
+	ckpt_msg_lock(ctx);
+	__do_ckpt_msg(ctx, err, fmt);
+	_ckpt_msg_complete(ctx);
+	ckpt_msg_unlock(ctx);
+
+	if (err)
+		ckpt_set_error(ctx, err);
+}
+EXPORT_SYMBOL(do_ckpt_msg);
+
+/* checkpoint/restart syscalls */
 
 /**
- * sys_checkpoint - checkpoint a container
+ * do_sys_checkpoint - checkpoint a container
  * @pid: pid of the container init(1) process
  * @fd: file to which dump the checkpoint image
  * @flags: checkpoint operation flags
@@ -22,14 +408,32 @@
  * Returns positive identifier on success, 0 when returning from restart
  * or negative value on error
  */
-SYSCALL_DEFINE4(checkpoint, pid_t, pid, int, fd,
-		unsigned long, flags, int, logfd)
+long do_sys_checkpoint(pid_t pid, int fd, unsigned long flags, int logfd)
 {
-	return -ENOSYS;
+	struct ckpt_ctx *ctx;
+	long ret;
+
+	/* no flags for now */
+	if (flags)
+		return -EINVAL;
+
+	if (pid == 0)
+		pid = task_pid_vnr(current);
+	ctx = ckpt_ctx_alloc(fd, flags, CKPT_CTX_CHECKPOINT, logfd);
+	if (IS_ERR(ctx))
+		return PTR_ERR(ctx);
+
+	ret = do_checkpoint(ctx, pid);
+
+	if (!ret)
+		ret = ctx->crid;
+
+	ckpt_ctx_free(ctx);
+	return ret;
 }
 
 /**
- * sys_restart - restart a container
+ * do_sys_restart - restart a container
  * @pid: pid of task root (in coordinator's namespace), or 0
  * @fd: file from which read the checkpoint image
  * @flags: restart operation flags
@@ -38,8 +442,49 @@ SYSCALL_DEFINE4(checkpoint, pid_t, pid, int, fd,
  * Returns negative value on error, or otherwise returns in the realm
  * of the original checkpoint
  */
-SYSCALL_DEFINE4(restart, pid_t, pid, int, fd,
-		unsigned long, flags, int, logfd)
+long do_sys_restart(pid_t pid, int fd, unsigned long flags, int logfd)
+{
+	struct ckpt_ctx *ctx = NULL;
+	long ret;
+
+	/* no flags for now */
+	if (flags)
+		return -EINVAL;
+
+	ctx = ckpt_ctx_alloc(fd, flags, CKPT_CTX_RESTART, logfd);
+	if (IS_ERR(ctx))
+		return PTR_ERR(ctx);
+
+	ret = do_restart(ctx, pid);
+
+	/* restart(2) isn't idempotent: can't restart syscall */
+	if (ret == -ERESTARTSYS || ret == -ERESTARTNOINTR ||
+	    ret == -ERESTARTNOHAND || ret == -ERESTART_RESTARTBLOCK)
+		ret = -EINTR;
+
+	ckpt_ctx_free(ctx);
+	return ret;
+}
+
+
+/* 'ckpt_debug_level' controls the verbosity level of c/r code */
+#ifdef CONFIG_CHECKPOINT_DEBUG
+
+/* FIX: allow to change during runtime */
+unsigned long __read_mostly ckpt_debug_level = CKPT_DDEFAULT;
+EXPORT_SYMBOL(ckpt_debug_level);
+
+static __init int ckpt_debug_setup(char *s)
 {
-	return -ENOSYS;
+	long val, ret;
+
+	ret = strict_strtoul(s, 10, &val);
+	if (ret < 0)
+		return ret;
+	ckpt_debug_level = val;
+	return 0;
 }
+
+__setup("ckpt_debug=", ckpt_debug_setup);
+
+#endif /* CONFIG_CHECKPOINT_DEBUG */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 28b42b9..df9a344 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1230,6 +1230,19 @@ config ASYNC_RAID6_TEST
 
 	  If unsure, say N.
 
+config CHECKPOINT_DEBUG
+	bool "Checkpoint/restart debugging (EXPERIMENTAL)"
+	depends on CHECKPOINT
+	default y
+	help
+	  This options turns on the debugging output of checkpoint/restart.
+	  The level of verbosity is controlled by 'ckpt_debug_level' and can
+	  be set at boot time with "ckpt_debug=" option.
+
+	  Turning this option off will reduce the size of the c/r code. If
+	  turned on, it is unlikely to incur visible overhead if the debug
+	  level is set to zero.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
-- 
1.7.2.2

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