How can we say that in PageInit the SizeOfPageHeaderData is expected to be max aligned? Am I missing something? There are lots of other places where SizeOfPageHeaderData is used, not MAXALIGN(SizeOfPageHeaderData).
Its maxalign is ensured by its size of 24bytes (which is maxalign'ed). I think if we change this to not-maxalign'ed value bad things can happen. So I've added assert checking for this value. I think it is similar situation for both page header and page special, I wonder why they've been treated differently in PageInit.
> 1. page special size is silently enforced to be maxaligned by PageInit() even if caller-specified specialSize is not of a maxalign'ed size. > 2. page header size alignment is not checked at all (but we expect it maxalign'ed, yes). > > I'd propose do both things in the same way: just Assert both sizes are maxalign'ed during page init. > > I dived further and it appears that the only caller, who provides not properly aligned page special is fill_seq_with_data() and corrected it. > > I am really convinced, that _callers_ should care about proper special size. So now PageInit() just checks the right lengths of page special and page header with assert, not enforcing size change silently. PFA my small patch on this. I'd propose it to commit if in the HEAD only likewise the commit 4c0239cb7a7775e3183cb575e62703d71bf3302d. > > What do you think?
I still feel that for special size let callers call PageInit with sizeof(special_structure) and PageInit do the alignment. Others may have different opinion.
On the patch itself, how can we say that other special sizes are max aligned except sequence_magic structure?
Alike for page header, it is ensured by the current size of page special in all access methods now (except the size of sequence_magic, which I've corrected in the call). If someone wants to break this in the future, there is an added assert checking in PageInit.
I think we should not maxalign both SizeOfPageHeaderData and specialSize manually, just check they have the right (already maxalign'ed) length to be safe in the future.
