Re: [PATCH 000 of 35] Refactor block layer to improve support for stacked devices.

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NeilBrown wrote:
To achieve this, the "for_each" macros are now somewhat more complex.
For example, rq_for_each_segment is:

#define bio_for_each_segment_offset(bv, bio, _i, offs, _size)		\
	for (_i.i = 0, _i.offset = (bio)->bi_offset + offs,		\
		 _i.size = min_t(int, _size, (bio)->bi_size - offs);   	\
	     _i.i < (bio)->bi_vcnt && _i.size > 0;			\
	     _i.i++)							\
		if (bv = *bio_iovec_idx((bio), _i.i),			\
		    bv.bv_offset += _i.offset,				\
		    bv.bv_len <= _i.offset				\
		    ? (_i.offset -= bv.bv_len, 0)			\
		    : (bv.bv_len -= _i.offset,				\
		       _i.offset = 0,					\
		       bv.bv_len < _i.size				\
		       ? (_i.size -= bv.bv_len, 1)			\
		       : (bv.bv_len = _i.size,				\
			  _i.size = 0,					\
			  bv.bv_len > 0)))

#define bio_for_each_segment(bv, bio, __i)				\
		bio_for_each_segment_offset(bv, bio, __i, 0, (bio)->bi_size)

It does some with some explanatory text in a comment, but it is still
a bit daunting.  Any suggestions on making this more approachable
would be very welcome.


Well, I hesitate to state the obvious, but how about:

#define bio_for_each_segment_offset(bv, bio, _i, offs, _size) \
for (bio_iterator_init(&_i, ...); bio_iterator_cont(&_i, ...); bio_iterator_advance(&_i, ...)) \
        if (bio_iterator_want_segment(&_i, ...))

While this doesn't remove the complexity, at least it's readable.

--
error compiling committee.c: too many arguments to function

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