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