On Wed, Aug 01, 2007 at 11:52:35AM -0400, John Stoffel wrote: > > Tejun> Avi Kivity wrote: > >> 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. > > Tejun> Violently seconded. > > How about it be made into a real function instead? I was reading > through the patch, but got timed out yesterday, so take this with a > grain of salt. > > I thought I saw a couple of macros defined to use this macro yet > again. Which I figured might be a problem is the passed in variables > get munged. > > In any case, why does something so complicated need to be a macro, why > not a function instead?
I agree and actually wrote about the same opinion in one of the replies. It might even be benefitial performance-wise due to smaller cache foot print. Thanks. -- tejun - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
