[Devel] Re: build breaks when checkpoint unimplemented by arch

[Oren Laadan]

On Tue, 7 Jul 2009, Nathan Lynch wrote:

> Oren Laadan <orenl at cs.columbia.edu> writes:
> > That's what I tried initially, but the problem is that sigset_t may
> > be defined differently for userspace - see /usr/include/asm/sigset_t.h.
> > In fact, for x86_32, it it is different, defined as 'unsigned long' 
> > (and NSIG defined as 32, so only 32 bits).
> 
> I noticed this, but I figured only the kernel definition was salient.
> Apart from debugging checkpoint/restart, why would userspace need the
> definition of struct ckpt_hdr_sigset?

I expect user space tools to at least:

- Assist in debugging c/r

- Assist users in reporting problems with c/r (especially since they
  themselves do not debug or hack)

- Convert checkpoint images from one kernel version to another

- Provide information about a checkpoint image, and even allow its
  manipulation.  This can assist developers in debugging their programs
  (e.g. to debug a crash you need to run a program for 30 minutes so it 
  ets up its state; instead of repeatedly running it, you run it once, 
  checkpoint, and then debug from a restarted version. A tool could 
  allow you to peek/poke inside the checkpoint and even modify data in 
  it).

- Or a tool that converts a checkpoint image to a core dump so it
  can be inspected with gdb.

I'm pretty sure others will find other uses to it...

> 
> For that matter, why would userspace need the definitions of most of the
> structures in checkpoint_hdr.h?  (Again, debugging purposes don't count:
> ckptinfo or similar developer utilities can be included with the
> kernel.)

Keeping the checkpoint header format understandable by user space (and 
immune to 32-64 variations) has been a requirement since day 1.

> 
> > Moreover, if you include <asm/sigset.h> in checkpoint_hdr.h, which is
> > also included by userspace, you get lots of compilations warnings,
> > because of other stuff included from the kernel's asm/sigset.h that
						      ^^^^^^^^^^^^^
					I meant:      asm/siginfo.h

> > isn't supposed to be included by userspace.
> 
> Can you provide examples of such warnings?  Are you building against
> "sanitized" kernel headers (make headers_install) or using them in
> place?
> 

Both.

Oren.
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