Em Thu, Sep 11, 2014 at 05:35:27PM +0200, Jiri Olsa escreveu:
> On Thu, Sep 11, 2014 at 12:23:30PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Sep 11, 2014 at 04:59:45PM +0200, Jiri Olsa escreveu:
> > > On Thu, Sep 11, 2014 at 10:29:11AM -0300, Arnaldo Carvalho de Melo wrote:
> > > > But then I had no use whatsoever for the ->ptr one at this point, so I
> > > > just nuked it, to keep _just_ what is used _right now_, and added the
> > > > comment to the changelog :-)
> > > if we are treeting tools/lib/api as 'external' lib, I think we should
> > > use 'void *' for priv and let the user retype it to whatever he wants
> > > but I dont care/insist here too much.. it just seems strange to me ;-)
> >
> > Ok, so perhaps it should be:
> >
> > struct fdarray {
> > ...
> > union {
> > int idx;
> > } *priv;
> > ...
> > }
> >
> > And then perf's evlist will use:
> >
> > fda->priv[fd].idx;
> >
> > Then, when we get the need for a pointer, we can go there and
> > add it to the union.
> >
> > This will make tools/lib/api/fd/ a little bit more friendly to
> > use outside the kernel sources, since then a new version will be source
> > code compatible (but not necessarily binary compatible).
>
> you lost me ;-)
>
> could you please make an example of the !compatibility you mentioned?
If I leave it as is now, when I add that void * pointer to each entry in
fdarray->priv[], I will have to change fdarray's users, i.e. right now I
will have to go and change evlist.h, i.e. every place that has:
fda->priv[fd];
will have to be changed to:
fda->priv[fd].idx;
If I instead change it to:
struct fdarray {
...
union {
int idx;
} *priv;
...
}
Then I will not have to change anything when I add that void * pointer
to the union.
> > If we commit to that we can't just go on and change all its
> > users as we can now do for things like 'struct sk_buff', 'struct sock'
> > and any other kernel data structures.
> > There are costs in making it 'external' in the sense you're
> > implying. I want to make it a bit less 'external' (in your sense), at
> > least while we initially implement new stuff like this one.
> and the costs?
> also I did not mean that union above, what I meant was:
> struct fdarray {
> ...
> void *priv;
> ...
> }
Yeah, that is what I am trying to avoid. This will make it use
sizeof(void *) for each entry, and I have no use for that right now. All
I need is sizeof(int) for each entry.
Remember, this is an array, so its not just a matter of changing:
int *priv;
to:
void *priv;
But since it is an array, it will use, in this case, double the space,
on 64-bit, for no gain _right now_.
- Arnaldo
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