[Devel] Re: [RFC v14-rc][PATCH 22/23] c/r: Add CR_COPY() macro (v4)

[Serge E. Hallyn]

Quoting Oren Laadan (orenl at cs.columbia.edu):
> From: Dan Smith <danms at us.ibm.com>
> 
> As suggested by Dave[1], this provides us a way to make the copy-in and
> copy-out processes symmetric.  CR_COPY_ARRAY() provides us a way to do
> the same thing but for arrays.  It's not critical, but it helps us unify
> the checkpoint and restart paths for some things.
> 
> Changelog:
>     Mar 04:
>             . Removed semicolons
>             . Added build-time check for __must_be_array in CR_COPY_ARRAY
>     Feb 27:
>             . Changed CR_COPY() to use assignment, eliminating the need
>               for the CR_COPY_BIT() macro
>             . Add CR_COPY_ARRAY() macro to help copying register arrays,
>               etc
>             . Move the macro definitions inside the CR #ifdef
>     Feb 25:
>             . Changed WARN_ON() to BUILD_BUG_ON()
> 
> Signed-off-by: Dan Smith <danms at us.ibm.com>
> Signed-off-by: Oren Laadan <orenl at cs.columbia.edu>
> 
> 1: https://lists.linux-foundation.org/pipermail/containers/2009-February/015821.html (all the way at the bottom)
> ---
>  include/linux/checkpoint.h |   26 ++++++++++++++++++++++++++
>  1 files changed, 26 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
> index 69d14c4..2e99c74 100644
> --- a/include/linux/checkpoint.h
> +++ b/include/linux/checkpoint.h
> @@ -117,6 +117,32 @@ extern int cr_read_mm(struct cr_ctx *ctx);
>  extern int cr_read_fd_table(struct cr_ctx *ctx);
>  extern int cr_read_file(struct cr_ctx *ctx, int objref);
> 
> +/* useful macros to copy fields and buffers to/from cr_hdr_xxx structures */
> +#define CR_CPT 1
> +#define CR_RST 2
> +
> +#define CR_COPY(op, a, b)				        \
> +	do {							\
> +		if (op == CR_CPT)				\
> +			a = b;					\
> +		else						\
> +			b = a;					\
> +	} while (0)
> +

Speaking from experience with similar sets of macros in capability.h,
I'd like to suggest renaming a and b.  Something like:

#define CR_COPY(op, SAVED, LIVE)			        \
	do {							\
		if (op == CR_CPT)				\
			SAVED = LIVE;				\
		else						\
			LIVE = SAVED;				\
	} while (0)

That way the next time I need to use CR_COPY, I don't have to
agonize over which argument goes where.

> +/*
> + * Copy @count items from @b to @a if op is CR_CPT (otherwise,
> + * copy in the reverse direction)
> + */
> +#define CR_COPY_ARRAY(op, a, b, count)				\
> +	do {							\
> +		BUILD_BUG_ON(sizeof(*a) != sizeof(*b));		\
> +		if (op == CR_CPT)				\
> +			memcpy(a, b, count * sizeof(*a));	\
> +		else						\
> +			memcpy(b, a, count * sizeof(*a));	\
> +	} while (__must_be_array(a) && __must_be_array(b) && 0)
> +
> +
>  #define cr_debug(fmt, args...)  \
>  	pr_debug("[%d:c/r:%s] " fmt, task_pid_vnr(current), __func__, ## args)
> 
> -- 
> 1.5.4.3
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