Re: VARATT_EXTERNAL_GET_POINTER is not quite there yet

"Tom Lane" <tgl@sss.pgh.pa.us> writes:

> Gregory Stark <stark@enterprisedb.com> writes:
>> "Tom Lane" <tgl@sss.pgh.pa.us> writes:
>>> I can't say that I find this a nice clean solution; but does anyone have
>>> a better one?
>
>> I'm thinking instead of having struct varlena (which you're not allowed to
>> safely use any members of anyways) we should just have a typedef to void*.
>
> I don't think we could imagine eliminating the struct name, especially
> not as a back-patchable solution; there would be too many random
> breakages.

Yeah, I wasn't thinking to backpatch that.

> It might work to change struct varlena's contents to something like
>
>     char        vl_len_[4];    /* Do not touch this field directly! */
>     char        vl_dat[1];
>
> so that the compiler wouldn't see it as necessarily having more than
> 1-byte alignment.  This would also not break any existing code that is
> following the rules (touching vl_dat has never been stated to be
> verboten).

Oh, that would probably fix this problem pretty well.

Touching vl_dat is only safe if you've either just allocated the object
yourself or you've already detoasted it. In which case we could be using a
struct pointer.

But if you have a plain old varlena which might be toasted or the return value
from GETARG_TEXT_PP then it doesn't make a lot of sense to have a struct
pointer at all. 

--  Gregory Stark EnterpriseDB          http://www.enterprisedb.com Ask me about EnterpriseDB's PostGIS support!