Re: [RFC v12][PATCH 01/14] Create syscalls: sys_checkpoint, sys_restart

Balbir Singh
2009-01-14T18:04:53Z

* Oren Laadan <orenl@cs.columbia.edu> [2008-12-29 04:16:14]:

> Create trivial sys_checkpoint and sys_restore system calls. They will
> enable to checkpoint and restart an entire container, to and from a
> checkpoint image file descriptor.
>
> The syscalls take a file descriptor (for the image file) and flags as
> arguments. For sys_checkpoint the first argument identifies the target
> container; for sys_restart it will identify the checkpoint image.
>
> A checkpoint, much like a process coredump, dumps the state of multiple
> processes at once, including the state of the container. The checkpoint
> image is written to (and read from) the file descriptor directly from
> the kernel. This way the data is generated and then pushed out naturally
> as resources and tasks are scanned to save their state. This is the
> approach taken by, e.g., Zap and OpenVZ.
>
> By using a return value and not a file descriptor, we can distinguish
> between a return from checkpoint, a return from restart (in case of a
> checkpoint that includes self, i.e. a task checkpointing its own
> container, or itself), and an error condition, in a manner analogous
> to a fork() call.
>
> We don't use copyin()/copyout() because it requires holding the entire

^^^^^^^^^^^^^^^^^^^ Do you mean get_user_pages(),
copy_to/from_user()?

> image in user space, and does not make sense for restart. Also, we
> don't use a pipe, pseudo-fs file and the like, because they work by
> generating data on demand as the user pulls it (unless the entire
> image is buffered in the kernel) and would require more complex logic.
> They also would significantly complicate checkpoint that includes self.
>
> Changelog[v5]:
> - Config is 'def_bool n' by default
>
> Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
> Acked-by: Serge Hallyn <serue@us.ibm.com>
> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
> ---
> arch/x86/include/asm/unistd_32.h | 2 +
> arch/x86/kernel/syscall_table_32.S | 2 +
> checkpoint/Kconfig | 11 +++++++++
> checkpoint/Makefile | 5 ++++
> checkpoint/sys.c | 41 ++++++++++++++++++++++++++++++++++++
> include/linux/syscalls.h | 2 +
> init/Kconfig | 2 +
> kernel/sys_ni.c | 4 +++
> 8 files changed, 69 insertions(+), 0 deletions(-)
> create mode 100644 checkpoint/Kconfig
> create mode 100644 checkpoint/Makefile
> create mode 100644 checkpoint/sys.c
>
> diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32.h
> index f2bba78..a5f9e09 100644
> --- a/arch/x86/include/asm/unistd_32.h
> +++ b/arch/x86/include/asm/unistd_32.h
> @@ -338,6 +338,8 @@
> #define __NR_dup3 330
> #define __NR_pipe2 331
> #define __NR_inotify_init1 332
> +#define __NR_checkpoint 333
^^^ extra tab
> +#define __NR_restart 334

--
Balbir