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

[Oren Laadan]

Serge E. Hallyn wrote:
> 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.

Good idea, done.

> 
>> +/*
>> + * 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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